So after being without my car for a month due to a vacuum leak on #2 cylinder, and then rebuilding my DRLA's, I spent monday tuning the car with a quick test drive, and then drove for about an hour and a half yesterday without issue. The car was fantastic on back roads and on the interstate. All the while my head temps and AFR were spot on perfect. I was stoked to be back on the road!

I go to start the car today, and of course, the AFR is way off to start. I figure I'm just going to have to tweak the carb sync a bit. Then as the car is warming up I see on my 4 channel head temp gauge, that cylinder #3 is conspicuously cold. The other cylinders all come up to their normal operating temp, but #3 is staying around 200 degrees and won't go warmer. The engine itself sounded 'off', like that cylinder wasn't firing.

I tried changing spark plugs. Nothing. I tried blasting out the idle circuit several times with compressed air from both the idle jet side and the mixture screw side. Nothing.
What else can I try?
I don't know what possibly could've happened overnight for this to happen. The car sat in the garage untouched.

Stupud question, but did you check the idle jet itself? Also, not that it matters, but what were your compression results? Never did see that data.

Yeah I blasted out the idle jet out too. I even swapped idle jets from 3 to 4 with no change.

I haven't gotten around to the compression test yet. After I got the carbs back on and tuned them, it ran better than it ever did so I didn't bother.
I guess I should get around to checking compression, but I don't feel like that's what the problem is.
If I smother the intake on #3 it behaves similar to the vac leak I had on previously on #2. The idle doesn't increase like it did with #2, but the AFR comes right back into the 12's. It can't be another vac leak, right? Every single gasket from the heads to the top plate is new, and every nut and fastener is secure and tight.

I also looked down into the carb while the engine was running and there's no fuel leaking onto the throttle plate.

Does this sound like an idle circuit issue? BTW, my plugs and wires are brand new.

Did you ever change out the spark plug wires? Distributor cap?

I replaced the plugs and wires, which had been on the car for who knows how long.
I haven't replaced the dizzy cap or rotor yet, but the ones that are currently on the car I replaced a little less than a year ago.

It's got to be electrical, if you have a dead miss in only one cylinder on a carbureted engine. You might have moisture in your dist. cap . Spray some wd40 in there and I'll bet it clears up.

Well it's got to be electrical if compression is ok....

If you have a timing light, clip it onto that wire to see if it's firing.
Just cause it's new does not mean it's any good.

Check them all.

I'll give that a try tomorrow. Those wires better be good, they cost me $75 from Tangerine!!!

I don't think it's moisture in the dizzy cap. Dry as a bone in there.

With the engine running, turn off the lights in the garage and look for arcing around dizzy, wires and the plug itself.

great reply done it many times,you really can see a lot going on.

You can also try spraying with soapy water. (old timers trick) but will create an easy path to ground.

Unisyn reads the same on all 4 venturis? Not just the 2 forward throats? You can easily raise the idle by using 1 of the idle speed adjustment screws. The other side will follow suit and raise the idle a bit so the pulsing of the needle smooths out. Try closing all of the bypass screws to start with a common baseline ( note the current setting on all four). Is the plug wire continuity the same on all 4? What effect does completely closing the idle air mixture screw on the bad cylinder at a stable idle have? After closing you should note a stumble. Perhaps a faint snapping back thru the Venturi or exhaust as you're forcing that cyl to go lean. No change? Suspect that idle circuit. All o-rings and metal caps in place?

Highly recommend you check compression. I had a simlar condition due to an open exhaust valve and a dropped valve seat in the head. With Quad Exhaust I could actually see droplets of gas blowing out one of the pipes.

With all of the issues you've been having, we need to follow one of the three paths (spark, fuel, air/compression) to completion. With new wires, even given their quality, I'd move onto checking spark first, at least at the plug wire. It's the simplest test, and the thing which has been modified most recently. Next,we need a compression test to rule out that path. Finally, we'll deal with the carbs. But if you follow Kevin's test with the Unisyn, it'll also indicated issues with compression or something mechanical causing the issue.

Compression results are in. Engine was warmed up, however I don't have anything I can use to squirt oil into the cylinders. Not sure if that matters. Readings were with WOT.

1) 139
2) 142
3) 144
4) 138

I think that's pretty good. I'm feeling a bit relieved to be able to rule out big $$$ issues.

I also tested the resistance of the wires from Tangerine.

1) 1.47 kOhms
2) 1.04 kOhms
3) 0.88 kOhms
4) 0.66 kOhms

Makes sense since 1 is the longest wire and 4 is the shortest, right?




I put the timing light clip around all 4 wires and I got an RPM reading from all of them.



I didn't see any arcing or spark scatter.



All 4 air bypass screws are fully closed. I can get pretty similar readings with the unisyn on all 4 cylinders. I haven't tried turning the mix screw all the way in. I'll give that a try next.
What I find confusing is that today I could warm the car up and it sounded like it's idling normally, and I can get pretty close readings with the unison on all 4, but I can't get the AFR back under mid 13's, and #3 cylinder will still not warm up past ~200*. If I let it idle until it's warm, it seems ok. But then if I rev it up anywhere past 2K rpm and hold it there the AFR will be back in the 12's momentarily, but then after a few seconds it'll start to pop like it's lean and the car starts to shake. Then if I get off the throttle it'll no longer idle at all and the AFR will be way up at like 17, and it sounds uneven like it did yesterday when I thought #3 wasn't firing. And after that there's no getting it to idle again until you shut it off and let it sit for a while.

I'm thinking it's got to be an issue with that carb on the passenger side. I'm going to pull it off tomorrow, take it back apart, and blast out every nook and cranny with air. Are the new gaskets I put on it ok to reuse since they've already been compressed?

I would say that's about the right direction to be going in, given the new data. One thing you might try before pulling the carb though is to pull the #3 spark plug wire with it running and check for arc between the wire and the engine. If it's definitely sparking, I'd suspect the carb. Still would try one last inspection/blowout of the idle jet on #3 first. If still there, then pull the carb. The gasket should be fine to reuse.

iffy plug? switch or put a new one in the problem cylinder

The next time it happens shut it off and remove the idle jet and look at it (don't blow on it) to see if there is crud on the tip. What happens sometimes is the idle jet gets clogged but when you shut it off, the crud drops back down in the hole so when you take the jet out it's clean.

Had this happen to me on a road trip and what I would do when it would misfire is shut it off and coast and then start it back up and it would run ok again until the crud would come back up.

You might be surprised with the vacuum readings after turning up the idle. While it's nice to have every thing equal at idle but that can change when the working linkage comes into play. It's a 3 minute test that is undone by turning a screw and you really don't disturb the current linkage setup.

Mixture screw on #3 went all the way in with no change in the idle at all. Looks like I'll be pulling that carb apart. There must be something stuck in one of the passages.
This is so irritating because it worked perfect before I rebuilt it.

But that would explain why it ran great one day and then not the next. Some little speck of something was just lying in wait to clog up the fuel passages.

Any time something happens just after I do some maintenance I look back at what I just did and go do it again. It usually works.

It feels like lately anytime I do any maintenance, something happens
At least I'm working all the bugs out. The car was soooo awesome on tuesday! Once I get this idle circuit cleared I'll HOPEFULLY be good to go! (There needs to be a 'knock on wood' emoticon for when you get too optimistic about how good your car is running)

So I've removed the carb and disassembled it twice now. Both times I've blasted air through the idle circuit passages, and all the other passages too. I studied the cutaway drawings in the Dellorto book to see where the passages lead to, and I'm able to tell that air is moving through the passages to where it's supposed to go. But still I can't get any response from that idle mix screw.

I think I'm going to try soaking the carb in something, and maybe that'll loosen up whatever's in there. Is there something strong you guys might recommend to soak it in that'll really clean out every little bit of it?

Or is there something else I should try first?

I've just about had it with these damn Dellortos. I've never had this much problem with a carburetor.

I had a problem with one of my Dellorto idle screws not responding. When I rebuilt them the problem went away. My carbs got water in them before the rebuild to the point that the spring in one of the diaphrams rusted in two. I soaked mine in Beryman Chem -Dip carbureator cleaner. Then I soaked them in Simple Green and water to neutralize the Beryman. Blew out all of the passages with spray carb cleaner and compressed air. There is some pitting on the inside of my carbs but they have worked fine for years that way. Once they are rebuilt and set up you shouldn't have to mess with them.

Unfortunately I just rebuilt them. I got one good day of driving out of them, where they performed perfectly, before this happened. Are those dips safe for brass? I'd rather not pull the throttle plates off if I don't have to.
Is there by chance an additive or something I can put in the float bowl that might help clear out any blockages?

One side of the engine having a problem tends to be a carb (on a dual carb engine).

One cylinder having a problem tends to be valves, compression, spark plug or ignition for that cylinder.

I would check:

Compression first.
Valve clearance second.

Then, swap plugs and wires on that side of the engine.

Then, change the distributor cap and rotor.

I've seen many spark plugs that looked great, but didn't spark.

Swap idle jets, main jets, emulsion tubes, etc around between the cylinders and see what happens.

With Joe. You already did the comp test. You already rebuilt the carbs. You already changed plugs and wires. Let's think back to how this problem started - it was running fine, then it stopped running correctly. Typically carbs don't just all of a sudden stop working EXCEPT for a plugged idle jet.

If you're SURE the idle jet is clear and there isn't some mystery debris behind it, then I'd be leaning towards an ignition issue. As Joe said, try swapping stuff around. Maybe try swapping #3 and #4 spark plugs. Did the issue follow it? If no, try swapping out another used plug wire on #3.

Also, is that spark plug on #3 wet? I mean, is fuel visible on it after you idle it for a few minutes? That is a dead giveaway that it's an ignition problem. If it was a plugged idle jet, the cylinder should not be receiving fuel and should not, in theory, be wet.

All of that has been done and/or tested, see page 1 of this thread. The only thing I can't do is swap wires because the MSD wires from Tangerine are cut so specifically to length that it's impossible. But I have verified it works by pulling the wire while the engine was running and letting it ground to the shroud. What a funny fuzzy feeling in my hand!



It's not a plugged jet, idle or main. I've swapped them around like musical chairs. There's never anything in the jets when I pull them except for fuel. What I do think it is, is a plugged/restricted idle circuit. Somewhere in one of the fuel passages in the body of the carb, something is hindering fuel flow.

I've swapped plugs around too. I even bought four new ones and tried them all. Plug isn't wet. I think the cylinder is getting no fuel, or not enough fuel, while at idle.

Okay. Now I'm tracking. Plug is not wet and you swapped others out, then I believe you're on the right track. It's likely a carb issue. Dellortos are fairly simple inside, but there are ways for them to get stopped up. It's far more common of Dellorto 45s, but there is a known problem called the Dellorto drip whereby a lead plug falls out in the main circuit an essentially allows fuel to drip into the throat at all times. However, your problem is opposite though it's conceivable that the opposite could happen if the plug dislodged in the right way.

http://www.thesamba.com/vw/forum/viewtopic.php?p=4836570

The only other thing I can suggest at the moment is to plug up the main circuit as best you can when you go to blow out the idle circuit and try to force as much air through there as possible, to blow out any crud that might be in there. You could also dip the carb, but instead, if you could isolate/plug the idle and main circuits, you might be able to inject Berryman's B-12 right into that circuit and let it sit. Then you don't need to worry about that stuff getting into the throttle shaft bearings.

Remove and rebuild that carb, again.

Check to make sure the,gaskets,have all the correct holes in them.

Dells have lead plugs that can dislodge?! Goddamn, I like these carbs less and less the more I get to know them. One more thing to worry about. That cutaway is great though. I guess I'll disassemble this carb for a 3rd time and blast all the passages out again. I'll try as you suggest to build up the pressure.

Rich, the gaskets are the same on both sides.

When you blow air thru the idle jet, out of carb, do you blow opposite of the direction of flow? Cans of compressed air work swell for blowing out passageways. Not so much pressure or volume but the plastic straws get up inside of the passageways. Hate to say it but it might be the time to send them out to a pro service. You certainly don't want to damage engine internals chasing a carb issue. The spark plug is completely dry after running the engine at a high enough rpm to get off of the idle/transition circuitry?

Try to artificially enrich the effected cylinder to verify your suspicions of lean mixture. You are doing a lot of work, and seems like repeatedly, before the problem is verified. If lack of fuel is the problem, this will temporarily solve it. The safest way I believe is to use propane enrichment. Hope this helps.

I'm feeling your pain. Can you switch carbs side to side? Maybe someone can loan you a carb. Another thing to consider is a valve sticking in the guide. I had a lawnmower that gave me fits to keep running - switched to a synthetic oil and valve train moved better after that. Just a thought

I've been blowing air through the passages from every direction that is possible. I've been using the cans of compressed air. Yeah the nozzles are great for getting all up in there!
I've got it apart right now. I just ran carb cleaner through every passage, and verified that fluid can move through all the passages, then blasted it out with the canned air. I'm letting it dry out before putting it back together and reinstalling. If it doesn't work this time, then I don't know.
I remember reading somewhere that there's a guy, I think it was in Utah maybe that people send their Dells to. Anyone know his contact info?

I haven't tried revving the engine up, just for fear of doing any damage. I guess it might be worth it to see if it starts firing once it transitions to the main circuit.




I'll give that a try if it doesn't work this time. Gotta go buy some propane first.

The Utah co WAS A.C.E. (Air cooled engineering). The owner sold it and it is/was still in operation under a dif name. I think the same techs. I had some 44s redone and smaller venturis install there. Very easy to deal with. Eric Shea or Jeff Hines might know the new name.

I've got a set of Dell 40s here that I'm going to rebuild, including pulling the plugs out and replugging the passages. No timeframe on that yet, but I'm going to write a how-to, sort of like I did for the Webers. If you're adventurous, you can tackle this yourself as well. Or if you can't get a hold of A.C.E. (who had a great reputation as I understand it), I can take a look at the offending carb for you. I am a new dad, so my time isn't "free", or all that plentiful, but I'll do my best if you decide to go that route.

I would say since you've gone through the trouble of pulling them off again, how about one more try back on the engine? This time, swap that carb to the other side. If the issue follows it, it's 100%, positively for sure an issue with the carb.

I just put the carb back on and still nothing on that cylinder. Zero response from the idle mix screw. I just don't get it. I watched carb cleaner fluid flow through every passage. I positioned the carb to test each fuel passage, and carefully metered carb cleaner through so I could visually verify that each passage was allowing fluid through. This doesn't make any sense. Is there any other issue that would cause the mix screw not to respond?

I'll try swapping the carbs later today or tomorrow. I need to walk away for a bit. I'm so frustrated with this car right now.

I need to figure this out soon. This car is my only car. I'm lucky that I work from home and that I can borrow my girlfriend's car after she gets home from work if I need to run an errand. But I've basically been without a car for a month now between this and the vac leak I had on #2. I'm just about at the point where I'm ready to buy a new set of carbs and call it done.

There's no possible way this could be a valve issue right? The compression test wouldn't have shown compression if a valve was stuck, right?

A search turned up ACE is now Blackline Racing. I'll contact them and see what they say.

That's it!

Hey,

Do you want me to ship you a set of bolt n ready Webers?
I am not using them at the moment, you can borrow them till you figure it out.
They are fairly newish copies, so not worn out at all.

A serious offer, but it won't happen till at least Tuesday, I am indisposed right now.
Let me know.

Rich

Hate to be a repetitive tool. You can blow thru the jet with your mouth yes?

It was funny to me, but i am bored out. My mind.

That's ok. Blowing thu a idle jet fresh out of the carb SUCKS. Ha. Then you taste fuel til the next store.

No worries! I appreciate you, and all of you guys, helping me troubleshoot this. Yes, I can blow through the jet with my mouth.



I will definitely take you up on that offer, thank you kindly! Sending pm!

I usually wipe it off first

The jet is not fouled.

You said they worked after you rebuilt them and then the next day they didn't. Are you absolutely sure you don't have a vacume leak on that cylinder? If you had a vacume leak at that cylinder maybe the idle adjuster screw for that cylinder wouldn't respond to adjustment. Just a thought...worth checking maybe use a spray bottle with water around the intake and see if you can find a leak.