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

I forgot about those....

I have a bag full that I ordered up for mine.

He makes a good point above.
the main difference is the length of the piston on the accel pumps.
Materials seem to differ, but it should not matter.

You need to make sure you have the right pumps..

Rich

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

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

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.

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).

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

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.

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

I've replaced worn out cams in the past. You have to remove the shaft to do it. I've seen rollers freeze up and wear the heck out of them. I can't recall if there were different sizes. Might not be from the kits I've seen and the reading you've done. I've got triples now and haven't rebuilt a dual in a few years. Did you measure the pump volume and check that both sides have the same size pump by-pass valve?

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!

Weak or failing coil?

Good call Aaron. That would be the next item to replace if this doesn't do the trick. At that point, with an all-new electrical system, I'll consider tearing into the freakin carbs again.

I agree. Although the realignement of the plates is not that hard, just removing the original self locking screws that hold the plates in place can bend the shafts if you do not back them up properly. BTDT.

Stu

I forgot about that Stu. I've screwed them up before too.

The biggest problem with realigning the plates in my opinion, is like many "wear" components, once they've worn into their respective throttle bodies, they need to be reinstalled in the same one(s). Of course when I rebuilt my first carbs, I wasn't really paying attention to that.

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.

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.

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

Weber pump part numbers

According to redline weber.

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

http://www.webercarbsdirect.com/40_IDF_Rep..._Parts_s/56.htm

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.

Remove the Compfire and try it with stock ignition.

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.

Maybe it's time for one of these

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

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...

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

I keep mentioning it and here is why.
There are MORE than two of these parts.

The key difference I have seen is the middle cam follower length is the longest on the old style (correct version) pump setup.

If you put in the shorter one (its not much shorter) you starve out at the top end.
Put one in that is too long (there is a long one that fits the old carbs) and you weap fuel all the time.

I have no idea how to know for sure which one is right except to replace them.
I got into this and ended up with about 5 different pumps before I had one that was correct for my carbs.

Every retailer swore what they sent was the right one, new part number, superceded part number blah blah blah.

I ended up asking a guy to send me one of each....
Tried them till one fit.
The outer rubber is the same, its the length of the middle portion that changes on every single one of them.


I also read earlier today that the air correction jets get clogged...but that would not account for a lean backfire like you are having.

Did you try the other carbs you have laying around?
I would go there at this point to get you focused on the issue....carbs or ignition.
rich

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?

Yes sir....you got it.

Like I said...btdt...

YOu know who knows all this is Art Thraen...who is now retired and sold aircooled engineering to blackline racing.

So, here is BLR,s phone number...they still do the work and Art is helping in the transition, but not for long.

801 747-3342
Rich

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

Finally. That sounds logical and lucid to me! Sorry it took so long to get it through my thick skull

I should have called Art a long time ago, but I knew he had sold the shop, so I wasn't sure if he was around to answer questions.

I might consider giving him a ring. In the meantime, I do have some extra of those diaphragms around from other cannibalized rebuild kits. I'll give them a shot when I get home. Next will be to try Tim's carbs.

It's a ten minute job, with instant results

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.

Click to view attachment


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.

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.

Click to view attachment


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.

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...ics/40IDF70.pdf

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?sho...carb&st=100


post 208

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

John, I'll check mine this afternoon when I start pulling them apart. But I've never noticed/seen the ball valve in them. Thanks for the information.


Rich,
If you could take a look at that, it would be a great help for me. I do believe the longer lever length from changing the fulcrum point might help.

I do have one of the adjustable pump covers and all the hardware included, but I've never been able to track down another for the other carb. I'm sure WeberCarbsDirect or someone sells the whole assembly, but it's probably exorbitant. On top of that though, I think that the cam that rides on the throttle shaft is different as well, and there is no way I'm going to pull both throttle shafts again just to change the cams out. Major PITA.

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.

No, Aaron, steady state is fine. Initially I thought that it was only happening at 4,000 RPMs or above, but what I discovered is that I can replicate it when I hammer the throttle above 3,000 RPMs. If I use partial throttle, I can actually get above 4,000 RPMs but as soon as I apply additional throttle, it backfires again.

To boot, there is a significant stumble now as well transitioning from no throttle to partial throttle. I had this problem before with small main jets, but solved it with larger 135 mains. It has slowly crept back though, and even 140 and 145 mains don't seem to help.

My goal is to pull the carb tops off, check the condition of the valves in the fuel bowls, clean/ream the accelerator pump jets and also probably move the pin down on the accelerator pump arm fulcrum.

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.

That would do it.

Hope that does it.

...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....

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

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

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

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?

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.