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Posted by: ThePaintedMan May 7 2013, 10:47 AM

Hello all,
Tonight I'll be buttoning up the car for the first DE this weekend (if it passes tech this time), and I've got one last thing I'd like to track down before hitting the track. A few times I've ventured into the 4,000 RPM range and I get a lot of backfiring, primarily from the passenger side carb, I think. Otherwise it runs great at all of the other RPMs. Right now it's got a crappy 009 distributor with points, but seems to work well enough so I've decided to stay with it to keep the headaches down.

Would it be logical to assume that the high RPM misfire is because of spark scatter with the points setup? I ask because I have a Pertronix unit ready to go on a spare distributor that I'd like to try, but with only a few days until the DE, I'm not going to go poking and prodding unless there is a good chance this could fix the issue. Otherwise I'll just short-shift


Whatcha think?

Posted by: DBCooper May 7 2013, 12:12 PM

QUOTE(ThePaintedMan @ May 7 2013, 09:47 AM)

Hello all,
Tonight I'll be buttoning up the car for the first DE this weekend (if it passes tech this time), and I've got one last thing I'd like to track down before hitting the track. A few times I've ventured into the 4,000 RPM range and I get a lot of backfiring, primarily from the passenger side carb, I think. Otherwise it runs great at all of the other RPMs. Right now it's got a crappy 009 distributor with points, but seems to work well enough so I've decided to stay with it to keep the headaches down.

Would it be logical to assume that the high RPM misfire is because of spark scatter with the points setup? I ask because I have a Pertronix unit ready to go on a spare distributor that I'd like to try, but with only a few days until the DE, I'm not going to go poking and prodding unless there is a good chance this could fix the issue. Otherwise I'll just short-shift


Whatcha think?

Posted by: ThePaintedMan May 7 2013, 12:24 PM

QUOTE(DBCooper @ May 7 2013, 02:12 PM)

Posted by: DBCooper May 7 2013, 08:23 PM

QUOTE(ThePaintedMan @ May 7 2013, 11:24 AM)

Posted by: jmill May 7 2013, 08:52 PM

What fuel pump do you have? Could also be you don't have adequate fuel pressure (volume). You'll notice it after a hard pull. Float level drops because pump can't keep up and you run lean.

Carb plumbed farthest from the pump will lean out first.

I'd look at stepping up on the main jet size if you have good fuel volume and it's not ignition related.

Posted by: 1988Hawk May 8 2013, 03:04 PM

QUOTE(ThePaintedMan @ May 7 2013, 11:47 AM)

Hello all,
Tonight I'll be buttoning up the car for the first DE this weekend (if it passes tech this time), and I've got one last thing I'd like to track down before hitting the track. A few times I've ventured into the 4,000 RPM range and I get a lot of backfiring, primarily from the passenger side carb, I think. Otherwise it runs great at all of the other RPMs. Right now it's got a crappy 009 distributor with points, but seems to work well enough so I've decided to stay with it to keep the headaches down.

Would it be logical to assume that the high RPM misfire is because of spark scatter with the points setup? I ask because I have a Pertronix unit ready to go on a spare distributor that I'd like to try, but with only a few days until the DE, I'm not going to go poking and prodding unless there is a good chance this could fix the issue. Otherwise I'll just short-shift


Whatcha think?

Posted by: ThePaintedMan May 8 2013, 03:32 PM

As far as I know, I've got plenty of fuel volume and pressure. This is a carter rotary style and I've got a quality inline regulator and gauge set to 3.5 PSI. No way to tell what's happening with the pressure when I'm driving, but when it's revved in the driveway I don't see any FP fluctuations. Even if that were the case, the passenger side carb is the one closer to the T (which is the one that I suspect is giving me issues). Would make much more sense for this to be a jetting/fuel issue than ignition if it's only one carb giving me trouble.

Think I might actually start with the mains. I've got 135s in there now and I have a set of 140s that I could try. Its possible my synch is off just enough at the higher revs and that I'm already borderline lean, so that at those RPMs it goes lean enough to start poppin.

No rev-limiting rotor on this distributor. Like I said, it might be easier to start with the jets since I know my way around carbs much more than ignition stuff. Eventually I'll probably look for a L-Jet dizzy and throw points on it just to cut down on the spark scatter if nothing else.

Thanks for the help and ideas!

Posted by: r_towle May 8 2013, 07:35 PM

First off, you ARE a wuss.....at a de, redline is where you play.

Get a timing light and see what it says when you rev it to above 3500.

You may need to set the timing differently

Posted by: jmill May 8 2013, 08:13 PM

Might be an ignition issue but if not and your looking for enrichment just towards the top end you can drop your AC jet size down below 2.00.

Posted by: ThePaintedMan May 8 2013, 09:38 PM

Well I threw everything I had at it tonight. Did it in steps - first bumped up to 140 mains from 135. Then F7 emulsion jets, which I had been meaning to install for awhile to try to improve the transition from idle to main.

Then I sucked it up and installed the Compufire. I tested in between with some bursts around the block and no difference. However, I did get it up to 4,800 once when it didn't backfire as much.

Ran out of time as I have to drop it off at the shop tomorrow before work to get it aligned. But when I get it back I'll play with the synch again. It's the only thing I can think of that would cause one bank to act up and not the other.

I may try those A/C jets though. I've been told 180s can really improve the top end over the stock 200s.

Posted by: old dog May 8 2013, 10:12 PM

QUOTE(ThePaintedMan @ May 8 2013, 08:38 PM)

Well I threw everything I had at it tonight. Did it in steps - first bumped up to 140 mains from 135. Then F7 emulsion jets, which I had been meaning to install for awhile to try to improve the transition from idle to main.

Then I sucked it up and installed the Compufire. I tested in between with some bursts around the block and no difference. However, I did get it up to 4,800 once when it didn't backfire as much.

Ran out of time as I have to drop it off at the shop tomorrow before work to get it aligned. But when I get it back I'll play with the synch again. It's the only thing I can think of that would cause one bank to act up and not the other.

I may try those A/C jets though. I've been told 180s can really improve the top end over the stock 200s.

Posted by: Racer Chris May 9 2013, 08:21 AM

Heck, I rev my street engine past 4K routinely - before upshifting, and once in a while in 5th as well.
I take it right to redline on a regular basis in the lower gears.
On the track you should be revving to 52-5500 rpm before every upshift.

Posted by: mepstein May 9 2013, 08:32 AM

If I didn't rev my little 1.7 past 4K, I wouldn't make it out of the driveway.

Have fun and good luck at the Track

Posted by: ThePaintedMan May 9 2013, 09:43 AM

Guess I've been babying her too much. I think it's my lack of funds and ability to rebuild an engine that causes me to be so careful with it. But if you guys say go for it, I don't need to be told twice

The car is at the shop getting aligned now. When I get it home, hopefully tonight, I'll play around with the synch some more and triple check for leaks. Chris, I have a quick question for you regarding your cable linkage. I'll send you a PM.

Posted by: rhodyguy May 9 2013, 09:59 AM

back firing on accel or decel? exhaust only, not out of the top of a venturi? what about stability at 4k cruise mode?

Posted by: ThePaintedMan May 9 2013, 10:04 AM

QUOTE(rhodyguy @ May 9 2013, 11:59 AM)

Posted by: ThePaintedMan May 9 2013, 07:39 PM

Hi guys,
Running out of time, but at least I think this is a simple problem. "Old dog" had it right. Vacuum leak at the base of the carb. Gaskets are all new, but check the pictures below. Any of you familiar with Weber IDFs know if this passage is supposed to be open? Are the gaskets supposed to cover up these holes? I've noticed it before, but figured they were supposed to be open to the manifold. I can't quite tell if they are compressed all the way, or if there is really a vacuum in this location. You can see the indentations in the gasket below.

Leaving for the DE tomorrow, so I'm hoping to get it fixed tonight. If the leak isn't coming from here, I can't figure out where it would be coming from. Nothing else stood out to me.

On that note, can anyone think of a quick fit that would get me through the weekend? I think Permatext grey is gasoline resistant.


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Posted by: jmill May 9 2013, 08:30 PM

Gasket is correct. Hole is correct. A vacuum leak would show up at idle and not 4K. I'd also take a close look at your linkage. If it's wonky you'll get pops. Show us a picture of your linkage.

Posted by: ThePaintedMan May 9 2013, 08:36 PM

QUOTE(jmill @ May 9 2013, 10:30 PM)

Posted by: r_towle May 9 2013, 08:40 PM

easy test

Switch carbs side to side and see if the popping follows the carb.

Still might want to consider checking the timing at full advance...
the 009 is not curved properly for our motors and it may affect your performance at full advance..
It may also not be delivering full advance.

rich

Posted by: jmill May 9 2013, 09:13 PM

That's a good linkage and wouldn't suspect that's your problem. Old worn out carbs aren't easy to troubleshoot. It would be better for your sanity to bite the bullet and purchase a new set.

We can make recommendations based on how the carb should perform but when other variables are in the mix (like worn out parts) it makes it very difficult to get it right.

Switching sides might narrow the problem down to the one carb. Actually telling what's wrong with an old broke down one will be hard to tell without holding it in my hands and seriously eyeballing it and maybe taking it apart. If they are old with worn out shafts I toss them over my shoulder and find better ones.

Posted by: type2man May 9 2013, 09:41 PM

You might want to check the plug wires or cap for arcing at higher rpms. Those are old Webers you are running.

Posted by: messix May 9 2013, 09:49 PM

check the dwell of the points, using gap only isn't always good enough.

and check to make sure that points and condenser wires are in good shape and connected tight.[ the connection under the cap]

and find or barrow a know good coil.

and ohm out your ignition wires with a volt ohm meter.

Posted by: rhodyguy May 10 2013, 08:25 AM

george, i consider the carb to intake gaskets a ONE time use part. get new ones. they should be dirt cheap if you have a vw parts outlet nearby. when you tighten the carbs down, do it in an X pattern, like torquing down lug bolts, in a few stages. if you're using cut steel lock washers, don't. schnoor/belleville (cv bolt washers) washers work great. with the impression in the gasket it looks like your reefing down pretty hard. if you do one nut tight you may be cocking the carb and building in a leak.

Posted by: ThePaintedMan May 10 2013, 11:49 AM

I agree with you Kevin, they are a one time use. Normally I wouldn't reuse them, but I'm stuck this weekend. Also, next time I won't crank down on them so much. I reinstalled the carbs last night and tried my best to check for leaks, but as far as I can tell, it must just be a leak from the inner portions of the throttle shaft. I have tightened them in the preferred "X" sequence as well (or as best you can with an even number of bolts).

I drove it to work today, as I'm leaving here for the DE. I did notice that once I got on the highway and it was warmed up, I could ease through 4,000 RPMs and it didn't do it. But whenever I was full throttle past 4,000 RPMS it would crack back through the throttle bodies like a SOB.

Posted by: monkeyboy May 10 2013, 12:05 PM

I would venture to guess that either the throttle shaft is leaking, or your accel pump needs to be looked at.

Posted by: ThePaintedMan May 10 2013, 12:18 PM

QUOTE(monkeyboy @ May 10 2013, 02:05 PM)

Posted by: jmill May 10 2013, 09:19 PM

With 55 idles, 140 mains and the F7 ET you shouldn't have any transition issues. You should actually be a bit fat. IMHO your mains are a bit too large. The 180 AC jets would enrichen the top end even more. If accel pump diaphragms are new and not wrinkled, check valves are good and fuel quantity squirt is the same on both carbs (actually measured) there's really only two things left. Float level is low or you have a decent sized vacuum leak.

One other thought, are the aux vents the same on both carbs? There's a few different ones.

Posted by: DBCooper May 11 2013, 06:30 AM

That sounds like a lean condition alright. It would have to be a really bad throttle shaft to only show up over 4000 rpms, but it makes sense that it would show up when floored and a lot of vacuum in the engine. Try switching the carbs from side to side, find out for sure where you need to be looking. Easy enough to do the same thing with plugs and wires, while you're at it.

If you can't go over 4K you aren't going to have much fun at the DE. On the bright side when you're done with this that's going to be the best tuned 914 around.

EDIT: Do your Webers have the little screen fuel filter on the inlets? Is it clear? If you switch side-to-side take a peek while they're off.

Posted by: rhodyguy May 11 2013, 06:52 AM

do your DE with a light foot. sounds like it runs rough enough that i'd be worried about breaking something. when you're back to investigating, close the bypass screws and see what you have for differing readings. should help to indicate the offending cyl. you may have to perform a leak down test. your carbs have the fittings for vacuum advance, yes? have fun this weekend.

k

Posted by: ThePaintedMan May 13 2013, 04:02 PM

Well you guys were right on a number of accounts. Though I did have a blast finally getting the car on track and an excellent instructor in T.C. (Carr914) who was patient with me, not being able to rev past 4,000 RPMs was a major handicap. I had to short shift in a lot of areas where I would have left it in fourth or third. You can check my build thread in my signature for the videos that T.C. posted and in some occasions hear the backfiring (though by the afternoon I was shifting before 4,000 to avoid it).

Over the next week or so I'll start by pulling the carb off and do a better inspection of the float level and if that doesn't do it, I'll swap the carbs left to right.

At the track I did notice that throttle position definitely has an impact as well. At 4,000 RPMs if I were to ease into the throttle, I could mostly eliminate the pops. But whenever I hammered into it, it made it worse. Needless to say, T.C. was very understanding. Thanks for the continued help and input folks.

The good news is, it never really ran hot. Only once did I get the oil up to 220 and CHTs were below 350-360 most of the time.

Kevin, these didn't originally have the fittings for vacuum advance. But they've been drilled for them and all the ports are plugged.

Posted by: r_towle May 13 2013, 05:54 PM

How far are you from TC or from URY?
Might help to have one of them (or both) over for a few beers to listen and poke around the engine bay with you...

rich

Posted by: Racer Chris May 13 2013, 06:41 PM

If you can partially mitigate the symptoms by engaging the pump jets, then one or more throats is going lean on the main fuel cirucut.

Posted by: messix May 13 2013, 06:57 PM

QUOTE(ThePaintedMan @ May 13 2013, 03:02 PM)

Posted by: jmill May 13 2013, 08:14 PM

QUOTE(Racer Chris @ May 13 2013, 07:41 PM)

Posted by: ThePaintedMan May 13 2013, 08:22 PM

Again, thanks for the ongoing advice gents. I hammered it again tonight while on the highway, this time at 3,000 RPM. When stomping on it, immediately to full throttle, I get a lot of lean backfiring. Again, only from the passenger carb. To me, this doesn't necessarily indicate an ignition issue (though I suppose it could be). The driver side seems to do just fine.

Here is what I've done so far to recap:
Changed distributors (still a crappy 009, but that only seems to be a problem on the low end with the flat spot)
Installed a Pertronix/Compufire
Installed F7 emulsion tube to richen things up throughout the rev range
Installed 145 mains on the offending carb, even though the other is still running fine on 135s

Still sounds like some kind of vacuum leak to me, but what do I know. Also, given the fact that this problem persists even after the initial accel. pump jet shot, (i.e. WOT) I don't think it's accel jet related. This weekend I'll pull the plugs and do a compression test to get a better feel for what's going on. Possibly a sticky valve, I dunno. Again, I'll play with the float as well and even swap sides with the carbs. But for now I'm just going to park it and be happy I made it through the weekend without blowing it up

John, these are the older style Webers without the ability to adjust the adjust the pump engagement. It's fixed.

Posted by: messix May 13 2013, 09:46 PM

QUOTE(ThePaintedMan @ May 13 2013, 07:22 PM)

Again, thanks for the ongoing advice gents. I hammered it again tonight while on the highway, this time at 3,000 RPM. When stomping on it, immediately to full throttle, I get a lot of lean backfiring. Again, only from the passenger carb. To me, this doesn't necessarily indicate an ignition issue (though I suppose it could be). The driver side seems to do just fine.

Here is what I've done so far to recap:
Changed distributors (still a crappy 009, but that only seems to be a problem on the low end with the flat spot)
Installed a Pertronix/Compufire
Installed F7 emulsion tube to richen things up throughout the rev range
Installed 145 mains on the offending carb, even though the other is still running fine on 135s

Still sounds like some kind of vacuum leak to me, but what do I know. Also, given the fact that this problem persists even after the initial accel. pump jet shot, (i.e. WOT) I don't think it's accel jet related. This weekend I'll pull the plugs and do a compression test to get a better feel for what's going on. Possibly a sticky valve, I dunno. Again, I'll play with the float as well and even swap sides with the carbs. But for now I'm just going to park it and be happy I made it through the weekend without blowing it up

John, these are the older style Webers without the ability to adjust the adjust the pump engagement. It's fixed.

Posted by: rhodyguy May 14 2013, 06:55 AM

when it's dark outside start the car and mist the the spark plug wires with a spray bottle and check for spark scatter. check the flanges on both ends of the intakes with a straight edge. when you run the comp test do a leak down as well. are you using phenolic (fi) intake gaskets? just guessing...weak valve sealing, spent valve guide? "misfiring during acceleration", 8 choises. #8 is interesting re jetting.

Posted by: r_towle May 14 2013, 11:26 AM

question.

Can you simulate this with no load?
So, can you make it backfire above 3000 rpms while your standing next to the car?

Rich

Posted by: ThePaintedMan May 14 2013, 11:46 AM

QUOTE(rhodyguy @ May 14 2013, 08:55 AM)

QUOTE(r_towle @ May 14 2013, 01:26 PM)

Posted by: yeahmag May 14 2013, 12:00 PM

A cheat for the manifold to head gaskets is to either use a non-hardening sealant or some axle grease. I've had mine trued up on a mill and still used the sealer. Hylomar Blue is what I've been using for a few years now.

Posted by: Racer Chris May 14 2013, 02:32 PM

QUOTE(ThePaintedMan @ May 14 2013, 12:46 PM)

Posted by: r_towle May 14 2013, 02:43 PM

QUOTE(Racer Chris @ May 14 2013, 04:32 PM)

QUOTE(ThePaintedMan @ May 14 2013, 12:46 PM)

If it only happens under load, that's usually electrical, correct? Unloaded would point to fuel delivery?

No.
You can't get the carbs onto the main circuit without any load on the engine.

Posted by: messix May 14 2013, 07:52 PM

I wouldn't go exposing your self to 40k of volts! it's not that I will kill you but that it can if you have the right circumstances kinda like Russian roulette!

I would run it up in rpm and grab a wire off the cap with some insulated pliers and see which wire has less affect on how the engine runs.

have you switched to electronic ignition yet?

I could be a bad cap or rotor... even if they are new.


when was you last valve adjustment?

Posted by: ThePaintedMan May 15 2013, 07:19 AM

Played around some more last night. I can still somewhat replicate the backfiring even when there is no load on the engine (i.e. in the driveway). It doesn't backfire as hard or as repetitively, but revving open throttle at 3,500-4,000 does produce some backfiring.

I did not witness any arcing last night, either through touch or visually. Went ahead and cleaned the cap and rotor, with no difference. I did not try the "pull the plug" test, but I can try that tonight. But to answer your question Rich, it is indeed much more of a repetitive "machine-gun" like backfiring. Which is the only thing making me think it's ignition - otherwise, all signs point to fuel delivery.

My other thought is to ask Tim (one of the guys I'm rebuilding a set of carbs for) is if he'll let me rebuild them and then swap them out with these carbs just to try to rule them out.

Yes, it has the Pertronix installed now. It didn't make a difference unfortunately.

While I had it running, I went ahead and put the car up on ramps so it could cool down so that I can re-check the valves tonight as well.

Posted by: ThePaintedMan May 16 2013, 08:29 PM

Checked the valves, everything was within spec.

Rechecked the wires tonight when it was much darker, and I could actually see an occasional arc from the coil wire and #3. It appears that where the wires clip into the holder on the tin has cause some very slight damage to the casing. I could produce some momentary arcing from that spot on each wire, which sucks because they were brand new 2 months ago. Took the wires out and taped them with some e-tape just to see if that fixed the problem. Went around the block and hammered it. No dice.

I'm going to order new carb to manifold gaskets, FI manifold to head gaskets, new wires and plugs. I'll try that next week and see what happens. If that doesn't do it, I'll see if Timothy will let me install the carbs I'm rebuilding for him as a last resort to see if it's really the carbs on this car giving me headaches.

Posted by: r_towle May 16 2013, 08:32 PM

Use some light rtv gasket between the phenolic spacer and the head, and between the spacer and the manifold.

Rich

Posted by: r_towle May 16 2013, 08:33 PM

So, you just replaced the wires, not too long ago.
Still have the old wires kicking around?

Rich

Posted by: jmill May 16 2013, 08:51 PM

My SWAG is still the accelerator pumps. I'm not real familiar with the real old ones but did your rebuild kit come with new cams? The roller wears the cam out and you won't get the right volume. It's been quite a few years but I recall they came with different sized diaphragms and cams. Did you install the larger diaphragm and cam?

Posted by: jmill May 16 2013, 09:00 PM

Just bombing around I see this fairly complete kit has three different sized diaphragms. No cams though.






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Posted by: timothy_nd28 May 16 2013, 11:33 PM

I'm new to this thread, by all means use my carbs! What's mine is yours, I hope they work better.

Posted by: r_towle May 17 2013, 06:16 AM

QUOTE(jmill @ May 16 2013, 11:00 PM)

Posted by: rhodyguy May 17 2013, 07:50 AM

so you noted arching on all 4 wires? unfortunately, with the pulley/cable linkage, the slave and master pulleys don't lend themselves to swapping the carbs left to right without reconfiguring the current setup. did you back the idle speed adj screw off of the slave side?

k

Posted by: stugray May 17 2013, 08:39 AM

If the carbs have a vacuum leak from the shafts, could some heavy grease or even oil seal the leak long enough to determine if that is the problem?
Obviously not a long term solution, but an easy troubleshooting step.

Stu

Posted by: rhodyguy May 17 2013, 09:54 AM

george, are the end washers, item #30 in the exploded diagram, in place? any chance you forgot one of the o-rings? one for each idle mixture screw and each idle jet.

Posted by: ThePaintedMan May 17 2013, 01:05 PM

From all the diagrams and stuff I've poured over, I don't think the cams can be changed, or were not intended to be. The different accelerator pump diaprhagms you see in the picture are for different model carbs. The later style, adjustable accel pumps use a different diaphragm than the earlier style (non-adjustable, like I have).

I did try to throw some grease on the shafts, both when I assembled the carbs and recently to try to seal out any leaks. Unfortunately they're almost impossible to get to with the carbs bolted up on the car, but good call.

Kevin, all o-rings are still there in place, and all are new. Yes, idle screws were backed off when I synched them. The end washers are in place on the throttle shafts to help prevent air leaks (plus I installed the newer style sealed bearings which don't leak like the old style ones do).

Posted by: r_towle May 17 2013, 02:20 PM

Early style carbs have three or four different accel pump dimensions...
I have the bag of parts to prove it...somewhere.

Took me several tries with several parts guys to get the right ones for the solid cam style carbs....the non-adjustable ones.

Rich

Posted by: URY914 May 17 2013, 02:30 PM

My car used to arc at the dizzy cap wires. One of the wires was arcing to the sheet metal. I could only see the arc at night. I cured it by making a dent in the sheetmetal with a hammer. .

I now have made several brackets to hold the wires off the sheetmetal.

Posted by: yeahmag May 17 2013, 07:30 PM

Have you verified wirh a timing light that nothing funny is happening at that RPM?

Posted by: jmill May 17 2013, 08:49 PM

QUOTE(ThePaintedMan @ May 17 2013, 02:05 PM)

Posted by: ThePaintedMan May 20 2013, 07:23 AM

Well I cleaned and re-lubed my SVDA dizzy and went ahead and installed it with the Compufire setup. Though it didn't fix the issue, it does transition a little smoother and idles better.

Now the driver's side carb is acting up as well, which leads me further to believe that this is ignition related. I think that in the process of tuning the carbs and the transition to the warmer months, the plugs are probably fouled. I went ahead and ordered a set of new wires and NGKs since that was the cheapest/easiest/most logical next place to start.

Rich, that is interesting that you have documented different cams for the accelerator pumps. I'd like to add that information to my carb thread at some point.

John, I haven't really found a way to measure the jet volume with the carbs on the car, but now that I've rebuilt these things a few times, I plan to do that for every carb that I rebuild for others. I knew that the cams *could* be changed, but I would honestly recommend that people avoid it if at all possible. As you remember, it involves removing the butterfly plates, punching out that little roll pin and then driving the shaft out of the body. I think that process subjects the throttle shaft bores to a lot of trauma and getting the plates to align the exact same way they did is a nightmare. On the carbs I'm rebuilding for some of the guys here on the forum, I've let them know that unless there is a well-founded reason to remove the throttle shafts, they should always be left in. I think that Tomlinson recommends the same thing in his Weber book.


Anyhow, I'll let you guys know what happens. I'm hoping it's just the plugs/wires!

Posted by: yeahmag May 20 2013, 08:25 AM

Weak or failing coil?

Posted by: ThePaintedMan May 20 2013, 08:35 AM

QUOTE(yeahmag @ May 20 2013, 10:25 AM)

Posted by: stugray May 20 2013, 08:39 AM

Posted by: ThePaintedMan May 20 2013, 09:44 AM

QUOTE(stugray @ May 20 2013, 10:39 AM)

Posted by: ThePaintedMan May 22 2013, 07:58 PM

Sorry to drag this back out, but I thought I would update on my progress, so if someone else ever has this issue it might help them shortcut and save all the time/money/hassle.

Purchased new plugs, wires and coil. Rather than try to isolate the issue, I was betting that replacing all of the ignition components at once would just get me back to better days faster. End result: nothing. Still a pretty good series of backfires at WOT at and above 4,000 RPM, now it's pretty much coming from both carbs.

So, as a last troubleshooting step and before I sink more money into it, I'll try to pull the carb tops off this weekend. I'm beginning to suspect that either all or at least one accelerator pump on each carb is not squirting sufficient volume. I'm back to having a large stumble when transitioning from idle to main circuits again as well, which leads me to believe they are the culprit. As of a few months ago, the car transitioned very well with little to no hesitation. It's possible some crap has begun to accumulate in the accel pump jets over time, I think.

The only other resort after that would be to take the carbs and manifolds off, install new gaskets and rebuild them both... again.

Posted by: timothy_nd28 May 22 2013, 08:25 PM

Take that extra set of carbs you have laying around and slap them on as it. If you have the exact same problem, the problem lies elsewhere.

Posted by: yeahmag May 23 2013, 09:35 AM

Have you verified with a timing gun that you aren't getting spark scatter at high RPMs?

Posted by: r_towle May 23 2013, 10:11 AM

Weber pump part numbers

According to redline weber.

47407-207, adjustable shaft
47407-027 , early style.

http://www.webercarbsdirect.com/40_IDF_Repair_kits_and_Parts_s/56.htm

Posted by: ThePaintedMan May 23 2013, 12:07 PM

Thanks Tim, I'm considering it.

Aaron, I timed it again last night, and although there is some scatter, I don't know what else could be done to fix it. I've tried 3 different distributors and installed the Compufire, along with new plugs, wires and coil. No difference.

Rich, I knew about the difference in diaphragms. I'm positive I have the correct ones (early style) installed.

Posted by: 904svo May 23 2013, 12:23 PM

Remove the Compfire and try it with stock ignition.

Posted by: rhodyguy May 23 2013, 12:37 PM

Posted by: ThePaintedMan May 23 2013, 12:53 PM

It was doing it with the stock ignition, as I have stated previously in the thread. I tried several different distributors, all with points. Then installed the Compufire. Neither way made a difference.

Posted by: carr914 May 23 2013, 01:07 PM

Maybe it's time for one of these

http://www.msdignition.com/info.aspx?taxid=8&taxid2=425

Posted by: yeahmag May 23 2013, 02:04 PM

The MSD won't help if it's not an ignition problem...

George, you don't have access to an LM-1 or some other wide band O2 do you? That would tell all...

Posted by: toolguy May 23 2013, 02:15 PM

Have you tried a new distributor CAP. . arcing inside, maybe cracked. .
The most common carburetor problem is bad ignition. .

Posted by: r_towle May 23 2013, 02:35 PM

QUOTE(ThePaintedMan @ May 23 2013, 02:07 PM)

Posted by: ThePaintedMan May 23 2013, 03:02 PM

Cap and rotor are brand new as well (on both types of distributors I tried.)


Rich,
I *think* I know what you mean now. Are you suggesting the CAM on the throttle shaft is not what differs from carb to carb, but instead the "button" length of the diaphragm can be different based on the kit purchased? As in, perhaps I'm getting a sufficient *shot* of fuel from initial throttle tip-in, but as it moves to WOT, the accel pump circuit actually closes, and it goes way lean on the very top end?

Posted by: r_towle May 23 2013, 03:07 PM

QUOTE(ThePaintedMan @ May 23 2013, 05:02 PM)

Posted by: r_towle May 23 2013, 03:12 PM

We just wanted to fill everyone in on what has been keeping us so busy over the past year and a half. We have been in negotiations with Art Thraen to purchase all of Air Cooled Engineering's equipment and assets. We reached an agreement and are now the owners and operators of Blackline Racing LLC. Justin has been working at ACE since 2008 and will continue to perform all of the engine and trans building, machining and service for Blackline Racing. Dave Hogarth has worked at ACE since 2005 and will still be performing all of the top notch carburetor work that ACE was known for. Colton will be leaving his current employment and running the business side of things to get work moving through better. We are currently working on a website that we hope to be up and functioning inside 3 months and we do have a facebook page if you would like to follow us on their.
This has been a dream of ours since we first started working together at our local VW shop 7 years ago. That dream only intensified when we saw what we could do with both of us working together on our Bonneville projects. We consider ourselves amazingly lucky to have this chance to make our obsessive hobby into our own business. We truly appreciate all the support everybody has given us; here in the forums, buying our lifters and inserts and of course out at the Salt.
We are very excited to start this new chapter in our story and are looking forward to what this means to the future of our Bonneville racing.

Thank you everyone,
Justin and Colton McAllister
Blackline Racing
801-747-3342

Posted by: ThePaintedMan May 23 2013, 03:13 PM

QUOTE(r_towle @ May 23 2013, 05:07 PM)

Posted by: timothy_nd28 May 23 2013, 03:33 PM

Next will be to try Tim's carbs.

Posted by: ThePaintedMan May 23 2013, 05:36 PM

Yeah, yeah Tim, I know This is more of a learning experience for me. Slapping your carbs on would be cheating!


So, I've pulled off one of the accelerator pump covers, praying that somehow I had installed the later style diaphragm designed for the adjustable lever rod, but I did not. As I mentioned, it's definitely the earlier style diaphragm, which, as Rich suggested, may come in a range of sizes. Getting the right one from the right supplier is probably a crapshoot. I do have two new diaphragms, which I'll install anyway, but below I've posted a picture of something interesting.

[attachmentid=387812]


I've known that these style accelerator pumps have two different positions for awhile, ostensibly to provide more/less volume depending on application. The question is, which one is which? Do any of you have the fulcrum pin in the #2 position in the picture above? Tim's carbs have it in #1, which is the only reason I'm hesitant to try to move the pin on my carbs.

Posted by: ThePaintedMan May 23 2013, 05:43 PM

Yeah, yeah Tim, I know This is more of a learning experience for me. Slapping your carbs on would be cheating!


So, I've pulled off one of the accelerator pump covers, praying that somehow I had installed the later style diaphragm designed for the adjustable lever rod, but I did not. As I mentioned, it's definitely the earlier style diaphragm, which, as Rich suggested, may come in a range of sizes. Getting the right one from the right supplier is probably a crapshoot. I do have two new diaphragms, which I'll install anyway, but below I've posted a picture of something interesting.




I've known that these style accelerator pumps have two different positions for awhile, ostensibly to provide more/less volume depending on application. The question is, which one is which? Do any of you have the fulcrum pin in the #2 position in the picture above? Tim's carbs have it in #1, which is the only reason I'm hesitant to try to move the pin on my carbs.

Posted by: ThePaintedMan May 23 2013, 06:17 PM

The only other things I want to take a look at when I pull the carbs apart again are the check valves. Now, I know that the bowl "exhaust" valve is located at the bottom of the bowl (#13 in the diagram below) and can sometimes get stuck, or wear out as it is a one-way check valve, so I'm considering replacing it on both carbs. However, there seems to be some confusion on the Samba that the "pump demand valves" (#10 on the diagram below) are also check valves. I have pulled enough of these apart now, that I have never seen a ball valve in them or any indication that there is a way for them to clog. Can anyone verify this?

http://www.webercarbsdirect.com/v/vspfiles/weber_carburetor_schematics/40IDF70.pdf

Posted by: jmill May 23 2013, 08:47 PM

If I recall correctly there is a ball check in #10. That's why they call it a valve. They clog or freeze closed. Then all the fuel or most goes to only one barrel. If there wasn't a check valve you'd suck air not fuel into your pump diaphragm.

They clogged up on this guy http://www.914world.com/bbs2/index.php?showtopic=100057&hl=carb&st=100


post 208

Posted by: r_towle May 24 2013, 07:33 AM

position 2 "would" make the lever depress the pump even farther....
Hmmmmm.

I will go out in a few minutes and take a alook.
I got mine working...so mine must be in the right spot...

I never saw that...but now that I have, I "must" try it.

Honestly, I was going to replace the whole thing with the adjustable setup, which I like better.

Rich

Posted by: ThePaintedMan May 24 2013, 08:50 AM

QUOTE(r_towle @ May 24 2013, 09:33 AM)

Posted by: yeahmag May 24 2013, 11:01 AM

Can you remind me if this happens at steady throttle state? If it's just the accelerator pumps not working correctly you should be able to slowly accelerate and the problem not be apparent.

Posted by: ThePaintedMan May 24 2013, 11:08 AM

QUOTE(yeahmag @ May 24 2013, 01:01 PM)

Posted by: ThePaintedMan May 24 2013, 06:43 PM

Okay, this is hard to explain... but I think I found the problem. When I had to pull the throttle shafts when I first rebuilt the carbs, I didn't know a whole lot about the ins and outs of these carbs.

The throttle shafts are drilled with an offset hole along the X axis for the accelerator pump cam. I believe I mistakenly swapped the throttle shafts, and the left one became the right and vice-versa. In other words, there appears to be a "left" and a "right" as you cannot get the accelerator pump cam holes to line up with the holes in the throttle shaft correctly if installed wrong. I assumed the PO had buggered them up and they simply wouldn't align so that I could get the roll pin to drive straight through them. Instead, it was probably my fault

This is an oversight that's easy to do, and I'm pretty sure it's whats causing the accelerator pump squirts to be mis-timed.

Will report back tomorrow if I can get them buttoned up and installed.

Posted by: carr914 May 24 2013, 07:09 PM

Posted by: jmill May 24 2013, 08:47 PM

That would do it.

Posted by: r_towle May 25 2013, 06:58 PM

Hope that does it.

Posted by: ThePaintedMan May 26 2013, 07:13 PM

...And it didn't do it


I dinked around with the carbs all Friday night and finally decided to go ahead and eliminate variables. I installed Tim's carbs, which were in much better shape as far as the throttle shafts and butterflies were concerned. They are the same, earlier type 40's with the cam driven accelerator pump. Just got it all bolted back together and took it around the block. Still a lean backfire at WOT, which can be replicated in the driveway or under load.

The only thing I have not tried, was to move the fulcrum pin on the accel pump down. This should provide more volume, especially at WOT.... at least, I think....

Posted by: carr914 May 27 2013, 08:40 PM

George, try changing out the Fuel Pump. When you couldn't get the car started here at my house, I was thinking it was starving for fuel, like it was in constant vapor lock

Posted by: rhodyguy May 27 2013, 09:23 PM

is the fuel pump elevation = or below the tank outlet?

Posted by: timothy_nd28 May 27 2013, 09:36 PM

You happen to have another set of carbs laying around? Third time's the charm

Posted by: ThePaintedMan May 28 2013, 08:05 AM

T.C. and Kev, the fuel pump is brand new and it is mounted on the back firewall over by the heater tube inlet for the long (which is slightly below the fuel line level). It also has a quality fuel filter inline before the pump. There is also a quality regulator on top, mounted to the trunk firewall set at 3 PSI and it splits into the two feedlines for the carbs just after that.

Tim, those carbs are awesome man. I rejetted them with the jets (50 idles and 140 mains) that I had in my carbs, and slapped them on. The throttle shafts are in great shape. I think you've found a customer I'll PM you about buying them from you. I'll probably just put these other ones on Ebay (listing their flaws of course) and be done with them.


Additional note though - when I visited Len in Tampa before stopping by T.C.'s, he mentioned that on his Triumph he had dealt with the timing marks being off on the harmonic balancer. Obviously we don't have to deal with that, but I'm starting to suspect that my timing marks on my fan are way wrong. Can anyone verify that the marks on the Bus fans are way different than ours? I advanced my timing by a good ten degrees or so on my way home and the car ran much better. No real stumble anymore, and it revs much better. Still a backfire at WOT, but it doesn't seem as noticeable. Should I keep going and add some more timing advance to see if it continues to improve?

Posted by: Mblizzard May 28 2013, 08:23 AM

George I had to go to 75s on the idle jets before all of my problems went away. I have not gone through all of the information here so you may have already done this. I have a set of 70s that I can send you if you want to try them out for a cost of a stamp.

Again you may have done that already so I make not be offering any help here.

Posted by: ThePaintedMan May 28 2013, 10:32 AM

Thanks for the offer Mike, but I don't think that would really have a big impact on a WOT problem. Much appreciated though!



Just thought of something - if I hook my GoPro up and post a video, would that help you guys better diagnose the issue?

Posted by: rhodyguy May 28 2013, 10:58 AM

prob not.

Posted by: Racer Chris May 28 2013, 11:31 AM

QUOTE(ThePaintedMan @ May 28 2013, 09:05 AM)

Posted by: ThePaintedMan May 28 2013, 12:48 PM

QUOTE(Racer Chris @ May 28 2013, 01:31 PM)

Posted by: Racer Chris May 28 2013, 01:31 PM

QUOTE(ThePaintedMan @ May 28 2013, 01:48 PM)

Posted by: ThePaintedMan May 28 2013, 02:01 PM

Thanks for all of the replies. Since I've tried just about everything, I did some more reading and it appears that when a cam starts to really get worn, one of the symptoms is a lot of backfiring/popping out of the carbs. The last compression test I did put all of the cylinders around 110 PSI, which is further evidence that this engine just might be flat worn out. It wouldn't surprise me if it is, as I don't have any indication that this engine has ever been rebuilt.

At least, it makes sense to me.

Posted by: r_towle May 28 2013, 02:02 PM

QUOTE(Racer Chris @ May 28 2013, 03:31 PM)

Posted by: timothy_nd28 May 28 2013, 02:44 PM

consider re-adjusting your valves to 0.004", it may help

Posted by: ThePaintedMan May 28 2013, 03:41 PM

Good call Tim, I might just try that.

Anyone know - Is there a way to measure valve lift on these engines using a dial indicator while the engine is still in the car?

Posted by: ThePaintedMan May 28 2013, 05:28 PM

Weird... went and drove it around the block after bumping the timing up about as far as it would go with the car still running. It still backfires at the same point, but I was able to "push" it past, and it then seemed to clear up and keep revving to 4,500.

Posted by: carr914 May 28 2013, 05:38 PM

Until it can rev past 6,000, it ain't fixed

Posted by: ThePaintedMan May 28 2013, 06:44 PM

Yeah... then I put it back on the ramps to go back to basics, mostly checking that I have the plug wires in the right order.

Posted by: vw505 May 29 2013, 09:53 AM

I guess you never had the heads off? I had a craked head once that would pop.

Posted by: ThePaintedMan May 29 2013, 07:31 PM

Reaffirmed that the SVDA was installed and timed correctly today. No difference.

I also adjusted the valve lash a little tighter than it was, which was probably closed to .008 than .006. REALLY quieted the engine down, but alas the backfire is still there, strong as ever.

Another thought I had - I guess it's possible this engine is a lot beefier than I might have ever anticipated and is just that thirsty on the top end. I've got new head-intake gaskets, manifold-carb gaskets and some smaller (read: richer) air correction jets on the way. I'm going to try one real rich mix for the top end before I give up on this engine, in case this is simply just an uber lean condition all along.

Still very strange though - each time I rev it up, sometimes the passenger carb is the one acting up, and then sometimes it's the driver's side now.

Posted by: r_towle May 29 2013, 07:50 PM

Did you rebuild the engine?

Posted by: timothy_nd28 May 29 2013, 07:54 PM

Could plugged or restrictive head vents cause this problem?

Posted by: r_towle May 29 2013, 08:04 PM

QUOTE(timothy_nd28 @ May 29 2013, 09:54 PM)

Posted by: ThePaintedMan May 29 2013, 08:07 PM

Crap, I didn't want this to start getting spread between two different threads, so I'll try to keep correspondence here.

Just posted in the "SVDA" thread:

This is indeed an old motor. The numbers I have for compression indicate it *may* have some life left (110 PSI on all 4) but I'm not holding out hope. I have no idea if, or when it has been rebuilt, but certainly not by me. Everything I know makes me believe it is the original, with over 100,000 miles and probably not rebuilt - there were no rebuild tags or markings on the engine when I got the car.

Rich - I'll post a video sometime this weekend. I've got a GoPro, and as long as I keep the windows up, it should get pretty good sound.


Also, no head vents. This is a '73.

Posted by: r_towle May 29 2013, 08:09 PM

Hahaha

To late, you started them....


So, what are the carb specs again please.
Body, venturis, jets and e-tubes

Posted by: ThePaintedMan May 29 2013, 08:11 PM

Carb specs:

Weber 40 IDF (early models)
Idles: 50
Mains: 140
Primary venturis: 28mm
Accel pump jet: 50
Bowl exhaust vent: 55
Emulsion tube: F7 (or F11, didn't make much difference, but F7s improved transition)
Main A/C jet: 200

Posted by: r_towle May 29 2013, 08:13 PM

This is a 1.7 liter motor?

Posted by: 904svo May 29 2013, 08:13 PM

Have you check your linkage to make sure both carburetors have the same travel?
What you describing is what happens when one carburetor is opening more than the other. To check this measure the distance from the throttle shaft to where the ball joint is connected they should be the same.

Posted by: r_towle May 29 2013, 08:15 PM

I asked in the other thread, post a pic of the linkage, or a few

Posted by: r_towle May 29 2013, 08:15 PM

With those specs on a 1.7 you are not starved for fuel.

Posted by: ThePaintedMan May 29 2013, 08:27 PM

Ack! So many questions, which really makes me happy... I'm just having a hard time keeping up.

Yes, I agree that my jetting settings should be more than adequate for a 1.7, based off of Tomlinson's Weber Manual tables.... that is, assuming it actually is a 1.7 and not some rebuilt monster In my dreams, right?

The linkage is a Tangerine Racing cable setup, which I am really happy with. From every indication I have, it is synched... it's really hard NOT to have them synched with this setup actually. I need to re-synch again tomorrow since I adjusted the valves today, but before I did the valves today, they were synched both at idle and at 3,000 RPMs.

Posted by: r_towle May 29 2013, 08:31 PM

Yup, that setup stays synced.

Hmmm

Did someone rebuild that motor at some point?
Starting to wonder about the valve timing....

Posted by: ThePaintedMan May 29 2013, 08:36 PM

QUOTE(r_towle @ May 29 2013, 10:31 PM)

Posted by: r_towle May 29 2013, 08:47 PM

May I suggest a slightly different way of adjusting your valves.
Pin the opposite valve wide open, then adjust the valve directly opposite that wide open valve.

Then you know you are on the bottom of the lobe.

If your ignition is correct, you have no manifold leaks, your linkage is setup, then it's back to the valve that may be opening to early for the intake stroke.

I have never built a motor with the valve gear off by one tooth, but this may be the result.

Try this.
Go for a run once hot....take it down the street and come back towards the house in a low gear, as its backfiring.......run it like that for about 100 feet then shut it off.
Do not let off the gas.
Kill the motor at the higher rpm,s on the main circuit, not on the idle circuit.

Then pull the plugs and rad them

Posted by: r_towle May 29 2013, 08:48 PM

Alternate would be to pull the oil pump and see if you have a stock cam gear, but even that could be put in wrong...

Posted by: messix May 29 2013, 09:50 PM

now that it is pulling good until the higher rpm i'm going with worn out/or broken valve springs.

Posted by: type2man May 29 2013, 10:38 PM

I think I mentioned this before but have you tried swapping out the cap, rotor and wires. It seems to me like something is arcing and higher rpm. With the carb setup you have, you should have no problem revving unless there is a spark problem or even a distributor problem.

Posted by: URY914 May 30 2013, 05:01 AM

Check your tire pressure.

Posted by: URY914 May 30 2013, 05:01 AM

Clean your windshield.

Posted by: URY914 May 30 2013, 05:02 AM

Move your seat all the way back.

Posted by: URY914 May 30 2013, 05:03 AM

Do your back-up lights work?

Posted by: URY914 May 30 2013, 05:03 AM

Check your heaterbox valves.

Posted by: URY914 May 30 2013, 05:04 AM

Change your underwear.

Posted by: URY914 May 30 2013, 05:12 AM

Try more brand in your diet.

Posted by: ThePaintedMan May 30 2013, 06:33 AM

Don't forget the blinker fluid Paul!

Posted by: carr914 May 30 2013, 07:40 AM

How are your Muffler Bearings?

Posted by: rhodyguy May 30 2013, 10:55 AM

leak down test. i think i mentioned this earlier. you should reconsider my "best offer". round trip would be about $32. running it to 6k with a fi cam (and old everything else in the valve train) is pointless unless you just want to make noise.

k

Posted by: ThePaintedMan Jun 1 2013, 04:30 PM

So here's what I did today. New manifold to head and manifold to carburetor gaskets. No difference. Tried richer air correction jets. No difference.

Here's video of the carbs (sorry it's so crappy - my GoPro wasn't charged). It's hard to see, or hear but you'll notice that the backfires are coming from the rear cylinders on each bank. This is reaffirming my belief that that lobe on the cam is flat/going flat.


https://www.youtube.com/watch?v=C7NnZ0cHyvs





https://www.youtube.com/watch?v=9OkSH-2iCGs



Kev, I'm still considering a leakdown test tomorrow, if it's not raining like it is today. If it is a flat lobe though, it wouldn't show up on a leakdown, correct? A leakdown can only help diagnose bad rings or valves, correct?

Posted by: rhodyguy Jun 1 2013, 04:50 PM

don't know what to tell ya. what the hell are the wires running down the drain funnel for?

Posted by: r_towle Jun 1 2013, 07:18 PM

If the camshaft was getting smaller, it would not open the valve...

It would not open the valve all the way.

It would not backfire.


Adjust those intake valve like I told you, and take your time.

Rich

Posted by: monkeyboy Jun 2 2013, 07:55 AM

QUOTE(r_towle @ Jun 1 2013, 06:18 PM)

Posted by: ThePaintedMan Jun 4 2013, 07:46 PM

Adjusted the valves per Rich's instructions, and everything was still in spec.

I worked until it was dark so I could try one thing. I pulled the plug wires off of first the #3 cylinder and then the #4 cylinder. Neither one made a difference in the idle, so the car essentially seems to be running on two cylinders. I checked both plug wire ends, and both were emitting good spark, so I know the plugs are at least getting spark.

Neither mixture screw is making much of a difference at idle now either. I cleaned both carbs well before they were installed, and I am at least getting a good squirt out of the accelerator pump jets, so I'm at a loss as to why the passenger bank isn't doing its part to keeping the engine running. It appears to be getting fuel.

Posted by: Mblizzard Jun 4 2013, 08:36 PM

If you really think that the spark is there then I would try adding fuel when at idle through the carb. OK I can't tell you how dangerous that is and how much I would tell you to only consider it as a last resort. But you sound like you may be close to that point. If the idle changes then I think you know there is a fuel problem in the idle circuit. That might be faster than swapping carbs from side to side.

Does nothing to solve your problem but it may point you in a direction. Another option to check the valves is to scope them through the spark plug hole. I just got a decent USB scope from Amazon for about $40 bucks. It seems to be ok nothing great but it can also be used to inspect your cam lobes through the push tubes. It was called the Supereyes 7. It has a 7mm head and can take pictures and record video to your Laptop. Might make you feel better about the cam if you can look at it. Just a thought.

Posted by: r_towle Jun 9 2013, 07:01 AM

Status?

Posted by: ThePaintedMan Jun 9 2013, 07:48 PM

Thanks for checking on me Rich. I went ahead and replaced the carb gaskets as well as the idle mixture o-rings, even though both were new, just to rule out the last variables.

The backfire is still there and as long as the engine is completely in synch, it seems like it's isolated to the #3 cylinder.

However, I did another compression test as well as a leakdown this weekend. Compression still shows around 105-110 on all 4 cylinders and the leakdown was phenomenal - I didn't see really any loss at all on any cylinder.

The only thing I can think of at this point is a weak valve spring, as this is a high RPM/high load problem. What do you guys think?

On that note, is it safe/recommended to replace one, or several valve springs on a older, even "tired" engine? I'd like to give it a shot at least before I pull the engine and install my spare.

Posted by: carr914 Jun 10 2013, 04:52 AM

4,000 RPM is not High RPM/Load

I still think you have a Bad Flux Capacitor!

Posted by: TurboWalt Jun 10 2013, 07:26 AM

QUOTE(monkeyboy @ Jun 2 2013, 05:55 PM)

QUOTE(r_towle @ Jun 1 2013, 06:18 PM)

If the camshaft was getting smaller, it would not open the valve...

It would not open the valve all the way.

It would not backfire.


Adjust those intake valve like I told you, and take your time.

Rich

Yes, it would. I don't know why, but my dad's car did exactly the same thing when his cam went flat. It would idle well, but almost any throttle would cause it to fall on it's face and backfire. But that was a V8.

Posted by: ThePaintedMan Jun 10 2013, 10:08 AM

Thanks for the reply Walt. It's something I've considered, but in theory, since both sides of the engine share the same lobe, I would have the issue on both sides, and a few people have already weighed in and doesn't think this is the problem.

Here is my logic for the weak valve spring:

Compression test is fine, and leakdown is fine. But on a compression test, we're only rotating the engine very slowly in relative terms, so the springs still have plenty of time to push the valve back closed, and as long as the valves are seating fully, there is no reason that the leakdown shouldn't be fine.

So what I think is happening is that one or both of the springs on #3 isn't supplying adequate force above several thousand RPMs, the symptoms of which simply don't show up on a compression or leakdown test.

I know this probably frustrates the hell of you guys, me asking a ton of questions, but as a student of science, I feel the need to find out the cause of a problem before I move on to other options. I'm searching through this to learn more about troubleshooting/diagnosing engine issues so that one day I'll be able to tackle a rebuild on my own.

Like I said, I have a spare engine, but I'd like to work through this problem to the end before I put it in. Then again, it's probably better to swap engines, and then I could pull the heads off of this one to better diagnose what's happening. What would you do?

Posted by: TurboWalt Jun 10 2013, 10:31 AM

A broken or weak valve spring could very well be the culprit. I had a BBC with big hyd roller cam that would chew up outer springs. It would present itself as mild miss or popping (not harsh like a backfire). I chased my tail on that one through the ignition system first. My headers kept burning up my spark plug boots which compounded things. I sorted that with ceramic boots. Try hooking up a vacuum gauge to manifold port and see if the needle is smooth or erratic. erratic would suggest valve spring issue.

Posted by: messix Jun 10 2013, 02:10 PM

He's carbed the needle will bounce on the 2 throat carbs. No plenum to smooth out the. Intake pulses.

You could have had the other motor in and running by now........

My bet now is bent valve or broken spring

Posted by: WLD419 Jun 10 2013, 04:26 PM

QUOTE(ThePaintedMan @ Jun 9 2013, 09:48 PM)

Posted by: yeahmag Jun 10 2013, 04:40 PM

Interesting... I've never used valve stem seals.

Posted by: ThePaintedMan Jun 10 2013, 08:49 PM

The generosity in this place never ceases to amaze me. Bill has already sent me a box of spare goodies before, and now this.



PM sent... I report back on whether this fixes it or not on an otherwise healthy engine.



I hope you realize what a great thing we have going here. Truly an amazing group of people.

Posted by: ThePaintedMan Jun 13 2013, 08:03 PM

Bill's tool and parts came in today and I can't wait to try to swap out springs this weekend. Thank you again Bill! While I'm at it I'm going to try to decipher whether the valve(s) are actually sticking in the guide too. I heard this occasionally does happen, especially with an older engine. This is why I'm curious about the possibility of a sticking valve:


https://www.youtube.com/watch?v=XExnP7wpafo




This was when the car was completely cold, and it happens almost everytime I try to start it when it's been sitting more than a couple of minutes. Does it tell any of you anything else? Again, it runs fine otherwise, until the backfiring issue.

If nothing else, the video is kind of funny...

Posted by: rgalla9146 Jun 13 2013, 09:19 PM

QUOTE(ThePaintedMan @ Jun 13 2013, 07:03 PM)

Bill's tool and parts came in today and I can't wait to try to swap out springs this weekend. Thank you again Bill! While I'm at it I'm going to try to decipher whether the valve(s) are actually sticking in the guide too. I heard this occasionally does happen, especially with an older engine. This is why I'm curious about the possibility of a sticking valve:


https://www.youtube.com/watch?v=XExnP7wpafo




This was when the car was completely cold, and it happens almost everytime I try to start it when it's been sitting more than a couple of minutes. Does it tell any of you anything else? Again, it runs fine otherwise, until the backfiring issue.

If nothing else, the video is kind of funny...

Posted by: edwin Jun 14 2013, 07:20 AM

If you can pull a plug off and it isn't affecting performance then I'd be really looking at firing order. That start up seems like leads going to wrong cylinders
Have you tried stopping by a mechanic and getting one to take a spin around the block? Surely worth a couple of dollars if they can shed any light at all as to what's happening
My money is on firing order or timing
Edwin

Posted by: old dog Jun 14 2013, 09:58 PM

QUOTE(edwin @ Jun 14 2013, 06:20 AM)

Posted by: ThePaintedMan Jun 15 2013, 10:45 AM

Below is a picture of the firing order on the distributor cap, as I have it set up. I'm pretty confident this is correct, but you can take a look for yourself.


Attached thumbnail(s)

Posted by: mepstein Jun 15 2013, 10:58 AM

Time for a 6.

Posted by: 904svo Jun 15 2013, 01:41 PM

Try this remove the cap and turn the rotor my hand and see if it returns. This will check the mechanical advance. It may be stuck.

Posted by: ThePaintedMan Jun 15 2013, 02:15 PM

QUOTE(904svo @ Jun 15 2013, 03:41 PM)

Posted by: 904svo Jun 15 2013, 03:34 PM

Have you check the resistance of each plug wire? They should be 5k ohms.

Posted by: r_towle Jun 15 2013, 03:50 PM

Move every plug wire on spot clockwise.

Posted by: timothy_nd28 Jun 15 2013, 05:24 PM

QUOTE(r_towle @ Jun 15 2013, 01:50 PM)

Posted by: r_towle Jun 15 2013, 07:53 PM

And reset the timing by turning the distributor clockwise till the edge of the vacuum can , the small top portion, lines up with the wire clip on the oil filler..
That should be close enough to start it and get a timing light on it.

Posted by: vw505 Jun 15 2013, 10:07 PM

Have you got the springs changed out yet?

Posted by: ThePaintedMan Jun 16 2013, 06:01 PM

Pulled both springs on the suspected cylinder (#3) with the handy tool that Bill sent me. Pulled the exhaust lifter as well to inspect - couldn't get the intake lifter to come out due to the ridge that forms.

Long story short, I compared the springs with known good springs and they look fine - same height. The lifter showed a little sign of pitting, but nothing major. I'll post pictures of that once I d/l them off my GoPro.


Took a drive, and it didn't make a difference.

Then went to Rich and Tim's suggestion about rotating the plug wires one spot clockwise. Tried to align the dizzy the way Rich suggested, but now it won't fire at all. If I continue moving the can a little further, I can get an occasional pop/loud bang out of the exhaust, but it won't fire. Here's what it looks like currently:


Attached thumbnail(s)

Posted by: ThePaintedMan Jun 16 2013, 06:46 PM

Nevermind. I got it by going back to the basics and setting it at TDC #1 and turning the dizzy till the rotor pointed at #1 wire. Which now means the vac advance can is wedged almost up against the tin/oil pressure sender wire.

Drove it around the block, same thing.

Are you sure you guys didn't mean rotate the plug wires counter clockwise?

Posted by: vw505 Jun 16 2013, 07:12 PM

Dude, time to pull the heads of and look for cracks.

Posted by: vw505 Jun 16 2013, 07:12 PM

Or swap out the motor.

Posted by: r_towle Jun 16 2013, 07:16 PM

remind me, what distributor is that again?

How are you determining TDC at number one cylinder?

Can you post a few pics of this process?

Every stock distributor is set as I stated...or damn close to the pic you posted above with the number one plug wire nearest the fan.

It still seems like an ignition issue to me....considering everything you have done so far.

Rich

Posted by: ThePaintedMan Jun 16 2013, 07:41 PM

Vw505, I'm getting dangerously close to that. I've got a spare engine, I just want to know WHAT the problem is before I pull the trigger, since compression and leakdown numbers are both pretty good. However, dicking around with this thing has mostly just wasted my time and money so far.

Rich, TDC determined via the markings on the fan and verifying that both intake and exhaust valves are closed on #1 (rockers rocking).

It's an SVDA distributor - more info here: (scroll down about 1/8 of the way, or search for "SVDA.")

http://www.ratwell.com/technical/FAQ.html



Could you elaborate as to why moving the spark plug wires 90 degrees would potentially solve a backfire on *one* cylinder though? In theory, if the plug wires are moved and the dizzy moved along with it, nothing else changes on that one cylinder, correct?

Posted by: r_towle Jun 16 2013, 07:50 PM

I would suggest that at the point of TDC you have the valve covers off and see what valve opens on the number one cylinder as you continue to rotate the engine.

If its the exhaust valve, then you were at tdc, if its the intake valve, almost right away, you were not.

Rich

Posted by: WLD419 Jun 17 2013, 03:23 AM

Hey George ,
I got nothing except maybe 1 dumb question ,do you got the spring in there between the distributor and the drive gear ( it keeps the drive gear from twisting
up&out and changing the timing ) maybe I miss that part of this post ,
sorry other then that I cant think of anything , watching that video ,it seems to
appear theres somthing to this timing Ignition thing , Good Luck Bill D.

Posted by: rhodyguy Jun 17 2013, 08:32 AM

does your distributor have a notch in the top edge of the body? the positioning of the #1 cap terminal pictured doesn't seem as i remember.

Posted by: ThePaintedMan Jun 17 2013, 08:36 AM

Rich, I'll give it a shot, but again, I don't see how my timing marks (this is the correct fan and it is bolted on properly) could point to TDC and the rockers be loose on that cylinder if it was not truly at TDC. I guess as you mentioned, it is theoretically possible that the engine was not assembled correctly and the valve gear is off. But this is a problem that seems to have developed over time - when I first got the car running, I never had a backfire. Which is *more* frustrating, given the decent compression and leakdown numbers. One would think that any problem that develops over time is a result of something mechanically wrong with the engine, or an incorrectly installed/broken part (read: dizzy, etc, but remember, I've replaced just about everything that isn't internal to the engine)

I do believe that you guys are on to something with the ignition timing, but I'm just having an issue conceptualizing why I would have a problem with one cylinder, but not others if it is indeed a timing problem.

Bill, that's a good point, but I do indeed have the spring installed in the drive gear.

Posted by: rhodyguy Jun 17 2013, 08:45 AM

rotor at notch on top distr body (if the body has one). 0* fan mark in the indicator notch. #1 wire terminal. doesn't need to be off by much to disrupt things.

Posted by: ThePaintedMan Jun 18 2013, 08:27 AM

Didn't have time to work on it last night, but I did some reading:
http://www.914world.com/bbs2/index.php?showtopic=108441&st=20

It might be possible that the distributor drive pinion (the offset fitting at the base of the dizzy shaft) is installed 180 degrees off. I pulled out the roll pin right after I got it so I could re-shim the pinion, and I guess it's theoretically possible that I put it back wrong.

It does not, however explain why I have the same problem with 3 different distributors though.

Posted by: rhodyguy Jun 18 2013, 09:08 AM

depends on the indexing and wire placement. if you are replacing the wires as before you're repeating the same behavior. the indexing being wrong is not so much in the distr as it is the dist driveshaft. the cog in the distr only fits one way into the shaft. look on pgs 64 and 65 for the text and fig 3.6 for the drive orientation @TDC.

Posted by: ThePaintedMan Jun 18 2013, 09:25 AM

QUOTE(rhodyguy @ Jun 18 2013, 11:08 AM)

Posted by: rhodyguy Jun 18 2013, 10:01 AM

no hard work involved driving a car with 235hp, ac, partial leather seats, and sat radio.

k

Posted by: r_towle Jun 29 2013, 09:12 PM

So,

You went off and bought a total chick car, and now you just stopped working on the 914?

Posted by: carr914 Jun 30 2013, 04:57 AM

Posted by: rhodyguy Jun 30 2013, 05:48 AM

richard, the "bought a total chick car" was directed towards me or george? i just want to be absolutely sure before i reply any further.

Posted by: edwin Jun 30 2013, 06:34 AM

I would assume its aimed at the miata that George bought.
Will be interesting to see if the msd changes the timing problem

Posted by: ThePaintedMan Jun 30 2013, 07:53 AM

It was directed at me . FYI, I haven't gotten to enjoy working much on either the 914 or the car. I have no garage down here in Florida, and it has rained throughout the day for the past, what seems like, 2 weeks. So during the summer my choices are: work out in the sun, or work in the rain. But thanks for the Rich, you're right, I need to get moving on it.

My next goal is to finish wiring the MSD as well as cutoff switch, since I know that currently the engine at least starts and runs fine most of the time. I'd like to get my wiring all set and reliable, then I'll swap out for this spare engine. So I'm not adding more unknown variables.

Posted by: ThePaintedMan Jun 30 2013, 07:03 PM

Didn't get to the MSD today, but I made some progress on my cutoff switch/ignition switch/push-button start. Not as much as I had hoped, as it seemed like everytime I went back outside, it would start to rain again. I feel like Charlie Brown with a cloud always following me around.

Wiring confuses the heck out of me. It's both an art and a science that I'm really not cut out for.

Posted by: carr914 Jun 30 2013, 07:27 PM

Everytime I turned around it was Raining - I must have gotten at least 3" at my House and it's starting again

Posted by: r_towle Jul 1 2013, 12:17 PM

QUOTE(ThePaintedMan @ Jun 30 2013, 09:03 PM)

Posted by: r_towle Jul 3 2013, 05:44 PM

So, how's that miata running?

Posted by: balljoint Jul 3 2013, 06:06 PM

All that rain has been my fault. I've been rain dancing non-stop to help those 12' trees take root.

I am still, however, waiting for George to figure this out.

Posted by: ThePaintedMan Jul 3 2013, 07:34 PM

I runs quite well Rich. And I even took the top down the other day to let the wind blow through my golden locks, just to piss you off.

Still working on wiring for now. Got a little work done yesterday and was GOING to work on it today till Dave must have started dancing. Hopefully sunshine the next few days, since my fiancee will be gone to the Keys for her bachelorette party. I have the driveway all to myself.

The plan is to finish the wiring in steps so I can check that I didn't screw anything up along the way. If the engine starts up again and nothing catches fire, then I'll start working on dropping it for the spare.

Hey Dave, if you're having any real dry spells, I learned a trick for planting trees and keeping them nice and watered at the roots. You can take 2 liter bottles and attach PVC at the end and push them into the ground till you get to the root ball/zone. Works like those little glass watering balls for household plants. Usually they'll last 3-4 days before needing to be refilled. You can also add a mixture of starter fertilizer that's high in phosphorous (20-20-20 works well) with the water to get them going.

Posted by: r_towle Jul 3 2013, 07:52 PM

Just don't let people see you with split ends....bad form.

Good luck with the wiring and I for one would like to do a triage on the motor to see why you think it may be the engine at this point.

If and when you take it apart, check the position of the timing gear in relationship to the crank gear and see if the dimple marks line up properly...before you pull the camshaft out of position.

Rich

Posted by: carr914 Jul 4 2013, 07:03 AM

QUOTE(ThePaintedMan @ Jul 3 2013, 09:34 PM)