So, for the past two weeks I've been trying to sort out the carbs. Since most Carb issues are actually engine/ignition related, I've spent some time working on the basics to ensure I can tune the carbs. To this point, I've:

1. Adjusted the timing (30 degrees BTDC)
2. Adjusted the Dwell (38 degrees)
3. New cap, rotor, points, wires, and plugs gapped at .60mm.
4. Adjusted the valves (Although, I may try this again as I've just discovered the backside methon on Pelican).
5. Ensured that I have no vacuum leaks at the manifold or the carb bases.
6. The throttle shafts feel very tight.
7. The floats are adjusted with the PMO float gauge and they are in between the two upper lines which is 33-35mm.

Here's the first issue. Barrel number three only pulls 3 bars while all other barrels pull 6 bars. I've tried to adjust it out but that's as high as it will go. I've cleaned the idle and main jets as well as the air correction and emulsion tube. Any suggestions on where the blockage is?

The second issue manifests itself at around 3200 rpms and above. I get a considerable amount of popping through the exhaust. This only occurs at cruising speed where the butterflies are barley open. If I give it some gas or go WOT, the engine pulls very strong and the popping is gone. Under 3200 rpm's, there is no popping. From what I've read, this is a rich condition. But, where do I start making the changes, in the main jets?

Finally, I just drove it a 100 mile round trip and here's the condition of the plugs. I don't know what to make of it. Is it too lean? I'm not an expert and would greatly appreciate some help to diagnose these issues.

Click to view attachment

I know someone would ask so here's how the carbs are setup.

Idle Jet=55
Main Jet=130
Venturis=32
Air Correction Jet=185
Emulsion Tube=F3
1969 2.0L "E" engine code with the following
Solex Cams
"S" pistons and cylinders
Weber 40 IDS triple throat carbs.

Everything appears to have been setup to "S" specs on the carbs except the air correction jets. From the Haynes Weber manual, they originally were 180's instead of 185. Any help would be appreciated. Thank you.

for the barrel that pulls less, what are its compression and leak down numbers? If you don't know, at least get a compression tester and find the compression numbers.

Aside from that, did you try fiddling with the air correction screw? its the little screw with a lock nut on it on the 2 barrel IDFs. I think it looks the same on the 3 barrel.

Did you rebuild the carbs? There might be a leak on the carb at #3 as well. Worth looking into. You will find balancing carbs is as much an art as science.

Zach

I had a similar issue recently. I had one cylinder sucking in a little less air that the other cylinders. Mine ended up being a head leak. There are several things that can cause a cylinder to suck in less air that the others.

I agree with the last post, you need to do a compression test.

The popping that you are hearing is probably a lean condition. Your spark plug looks lean.

Once you do what the others said, try filling up with 89 or above octane and see if that helps.

I did a compression test a few days ago it was about 10 PSI less than the other cylinders. The engine just recentley had a top end refresh. I replaced all of the seals as well as the rings and made sure the pistons and cylinders were in spec before they were reused. The valves and the seats were reground and the heads were planed to ensure they were flat. All cylinders were pulling a 120 PSI and this one was 110. The adjustment was made with the air correction screw and that's as far as it would go. Before the engine work, I vaguely remember this same issue. I think I'll try swapping the carbs and the piston banks and see if the issue follows. At least then I'll know it's internal to the carburator. The carbs were rebuilt last year and I've only used 93 octane since I've run the engine.

As you stated, recheck your valve lash. If the intake valve lash on cyl 3 us too loose, the valve will not be open as long, sucking in less air.

That being said, I thought that I should clarify why we are saying to do a compression test. Other than the above mentioned valve issue, a blockage is unlikely. What is more likely is that there is a head leak or something like that. If you have a head leak then when the piston retracts and sucks air into the cylinder- it will pull air from the carb and from the leak instead of only through the carb (ask me how I know ). This will make it look like the cylinder is sucking less air using a syncrometer however it is simply partially bypassing the carb.

Sorry about this post- I didn't see that you had done a compression test.

do you have leakdown? You can have great compression but crap leakdown numbers. I have seen it with my own eyes.

Is that 120 with the engine warm with the throttle open, or cold? 120 seems low on a fresh rebuild, even if the rings have not seated yet. My /4 was making 145 after a rebuild, and I think the /6 engines are supposed to have better compression numbers then the /4s. But I could be wrong there.

Zach

The engine was warm and the throttle was not open. I'm thinking I need to look at the valves again. It sounds like they may be too loose on a cylinder or two. I'm wondering if I may have a crack in the intake manifold around that carb. I put some propane to the base and didn't see a rise in rpm's. I don't any leakdown numbers. That's a test I haven't performed yet. From what I understand, you need an air compressor which I don't have. Obviously, it's pulling air from somewhere. It'll just take a little time to sort out. Thanks for the help.

Several questions: what is the fuel pressure at the carbs? On the Webers I had on my six in the race car we generally ran 3.5#. Did all the plugs look like that? If so then a slightly weak cylinder would not cause this. Why is the spark plug gap so high? do you have a MSD box and what is the voltage at the plug? If possible see if you can find someone that has the SnapOn voltage tester that fits over the plug wires at the plug and will tell the voltage when the engine is running. On my race car at idle the voltage with a MSD bos was approximately 14,000 volts which made the plugs fire great. What type of wires did you use? If you have a MSD box they really like the 8 or 9mm silicone wires and are hard to get for Porsche 6's. If you have conventional ignition that stock wires are best.

You said the throttle shafts are tight. Is this with the cross bar hooked up and how do they feel if they are pulled from the intakes? Has there been any porting work done on the intake side of the heads and corresponding intake manifolds? If so I would pull them and look very closely for cracks as my race car had 3 of the 6 intake manifolds cracked where some polishing to match the heads were done and we finally did a check as we could not get the mixtures to match up on all the cylinders. I had to buy a set of PMO intake manifolds! Anyways the the tight shafts are a sure sign the carbs are being pulled due to misalignment possibly.

Yup, could be pulling 'unmetered' air from a manifold leak or some such. Valves is the easiest thing to check.

I'm running a standard CDI box with clewitt wires. The gap was set to the recommended setting of .6 in Waynes book on rebuilding 911 engines. The fuel pressure is right at 3.5 pounds. All the plugs when pulled looked like this. I think I've found an assembly error when I timed the engine. I marked TDC on the pulley with white paint. It appears this white mark is 30 degrees before TDC as when I time it with 30 degrees advance, the white mark lines up with the case halves. So I guess my new questions is how big of an error is this? I set the cam timing and valve adjustment with this mark. Do I need to pull the engine and reset the timing, or can I adjust with the distributor? Thanks. I'll look at the manifolds and see if I can see any visable cracks.

I'll leave the timing question to the experts in engine building. For the manifolds you will have to pull them probably as with mine the cracks were not visible when mounted to the heads. I also installed new phenolic spacers as the old ones were sort of crushed, I guess I should never have "just snugged them a bit more" now and then when doing a pre-race check over! When the carbs are off that is the best time to check the shafts also.

Did you say you have IDS carbs? If so are the "candy canes" still installed or have they been blocked off correctly? The folks at Pierce Manifolds told me if they are not blocked right then some flood over will occur. I left mine installed as they suggested and extended them since I had some short velocity stacks and at 6500RPM I could actually see the A/F meter do a slight jump to richer!

I got the timing figured out and fixed. It turns out I timed it correctly at the Z1 TDC mark but, I was a tooth off on the dizzy. I pulled the dizzy, readjusted, and retimed and there's an amazing difference. The bottom end has a noticeable improvement in power and the popping at the top end has all but dissappeared. The idle is also stonger. Now, I can with certainty look at the carbs and manifolds for leaks. The "candy canes" are still attached. I removed the drop links on the carbs and there still seems to be very little play in the shafts. I'll pull the right bank tomorrow. I also want to look at the butterflies as I've read that if they're not closing correctly, air could be pulled through there.

I pulled the right bank the other day. I think I found the suction issue on #3 but don't know for sure. When I hold the carb up to the sun light, #'s 1 and 2 throttle plates have a little bit of sun light that illuminate the entire edge of the plate. #3 is completely closed with no sun light showing through. Could #3 throttle plate be my air suction problem? Is it so closed that it's cutting off the amount of air being pulled through the carb? Air is still being pulled through but at half the rate as the other barrels. I made an adjustment to the shaft on #3 and now all throttle plates look the same with the same amount of light coming through. I'm going to recheck the float heigth while I'm in there and give everything a general cleaning and reassemble with new gaskets.
The only other question I have is about the heat insulators. Does a gasket go between the heat insulator and head or just the heat insulator and carb? Thanks for the help, it is appreciated.

Sounds like you're on the right track. As for the insulator blocks, you want gaskets on both sides.

Throttle shafts can twist if you don't have your throttle stop set correctly. Be sure the travel of the pedal is limited correctly and the stop set so the carbs don't act as the stop themselves.

Mine is not setup correctly. I found a good write up on pelican on how to adjust. I'll readjust when I put the right bank back on. Thanks Gint for the info on the gaskets. I guess I'll be placing another order.

I realize this thread is over 6 months old but I wanted to add an update as I had great success with the motor last night. The first of the initial issues was in cylinder #3. This cylinder was not pulling the same amount of air as the other cylinders. It turns out that the butterfly was not adjusted correctly. It's now pulling the same amount of air as the other cylinders.
One of the overlying problems with this engine was I could not get it to idle. It would slowly decrease in rpm's until it stalled out. I pulled the intake manifolds off because I had a suspicion that I was not getting a good seal. Turns out that the manifolds were old and pitted. I took them to a machinist to have them resurfaced and they basically crumbled when he tried to remove the studs. I bought a new pair from PMO and that issue was resolved.
The last thing(s) that I did was follow a basic carb checklist that encompassed a whole engine management approach.

1. Check the timing and dwell
2. Adjust the valves
3. Engine had good compression. Initially I was getting low numbers but once I realized you complete the test with all of the plugs out, engine warm, and the throttle open, the numbers were 150+
4. New spark plugs, wires, cap, rotor, points
5. New gaskets for the heat disapators
6. Floats adjusted with the PMO tool
7. Tight throttle shafts
8. Following the sequence for balancing the airflow between carbs and then from side to side.
9. Understanding the differences between popping from the exhaust, popping from the carbs, and back firing through the carbs.

I'll admit that it was a slow methodical process. But, the end results was well worth it. The car idled at 1000 rpms last night for over 20 minutes and I only had an occasional back fire which I believe is an exhaust leak. I took it out last night and it's amazing how fast it is. I was up to 90 in no time and it kept pulling strong. For good measure, I ordered a Gunson Color Tune tool to ensure that I have the correct air/fuel ratio in each carb. I wanted to thank the world members who have been through this before. Without being able to search through and read hours of posts, this would not have been possible.

Awesome! It's so gratifying when things work out.

Only seems useful for idle, but still neat!

http://www.youtube.com/watch?v=B_ksmZLch0w

Here's another update. Mechanically, the engine is in great shape. I've learned a lot over the past several months and have found that you need to make sure the timing, valves, plugs, fuel pressure etc.. is correct before you play with the carbs. The last issue that I have I think centers around my idle jets. I am able to balance the air flow between all carbs and from side to side. Here's some of the settings and performance of the mixture adjustment screws.

Setting Low End Top End
1.75-2.0 Turns Sluggish stalls Fantastic with alot of power
2.5 Turns Sluggish, stalls Mediocre, a little rich
3.0 Turns Idles strong Sluggish, too rich

I'm wondering if my Idle jets are too small and not allowing enough fuel into the combustion chamber at idle. It feels as if the transition occurs around 1,400-1,500 rpms and if I leave the mixture adjustment screws at the 1.75-2.0 setting, there's a lot of power but the engine won't idle. Am I on the right track? Should I buy some idle jets larger and smaller than what is currentley in the car and experiment. Any help would be appreciated. Thank you.

might want to research what emulsion tube is best.
It will change the transition location and may alleviate the headache.

For a six, I have no clue which tube would work best...
rich

Read this - http://www.performanceoriented.com/technical.htm

From your description I'd say your too big on your mains and your idles are just a pinch undersized.

That's some good reading. I spent a couple more hours on it tonight. I'm going to try a couple things. I'm going to get 60 and 65 idle jets and try them out. I think the mains are appropriately sized. When they kick on, it's nice smooth power. I'm also going to try to run hotter plugs and in the next couple of weeks add an MSD system. Does anyone have a good idea of what plug to try?

I'm very far from a carb expert but have been looking at various other user
data from plenty of searches while setting my 2.2E. For idle jets, I have _NEVER_
seen anyone who has to run larger than 55 for small displacement non-race
motors. Changing those is probably a waste of time.

You may be right. At this point I have so many hours into the engine and carbs that It can't hurt. I'm at least to the point where I have a consistent idle and top end power with very little back firing. My backup plan is to take it to Stuttgart Motors in Loiusville if the jetting, plugs, and MSD don't work.

Success!! I received 60 sized idle jets in the mail today and what a world of difference it made. Now I have real smooth and consistent idle and the hesitation is all but disappeared. I may try 65's just to make sure but I drove the car for 45 minutes tonight and all is well. I hear an occasional back firing through the exhaust. I need to trace it down and see if I have an exhaust leak.

Hey Ericv1,

Why I believe you have a real issue with the Low vacuum of #3 cyl, I'm more concerned about your spark plug: it is SCREAMING LEAN!!! Being SO WHITE after 100 miles tells me that the engine is lean and running HOT! Running this way could cook your engine in the next few-hundred miles!! So I'm thinking larger jets are necessary.

I also agree with the suggestion of getting a compression check, if not a leak-down test. Harbor freight has a leak-down tester for under $40 and can give you a measure of each cylinder health based on a percentage of the 100 PSI pumped in.

If you do the compression test, be SURE to jam your throttle OPEN so your reading is not effected by closed butterflies.

Best of luck,
Terry

here is a great thread for carb tuning. http://www.thesamba.com/vw/forum/viewtopic...asc&start=0

Eric,
Go see Forey at TD Performance in Forest Park. He can help you if you are still having issues.
Van

I'm no expert, but I've been through my carbs a few times and I've read the book and thought about it a bit and here's what I've been thinking reading this thread.

If the popping is happening at 3200 and above then it is lean in the main circuit, not the idle.

From my experience and I think it says the same in the book, the air correction adjustment, even though the whole purpose of it is to 'even out' the pull of the cylinders to compensate for their differences, DOESN'T WORK. You may be able to use it a tiny bit to even out your idle, but even a tiny bit there will throw the whole thing off at anything but idle - you will not be able to get your mixture right through the rpm range if the air correction screws are off cylinder to cylinder - better to have 2 barrels that vary - though 3 vs 6 'bar' (whatever that is ) sounds like too much a difference for there not to be something else wrong, though I guess that reading was from early on and probably the valves... Just my .02

I've got that, is what I used to confirm the air correction screw thing. It has 2 'tests' in the instructions. You set it up to idle, between the blue (lean) and orange (rich), then bring it through rpms up to 2500 or so. It's supposed to richen (pump jets) but then go back to in between. You'll be too blue after that squirt is used if your mains are too small, air (?) jet is too big, or, like I said that 1 barrel with the butterfly adjusted out -
that is what the air correction screw does after all, make minute adjustment to the butterfly. Problem is it is different throughout its movement, not just at idle.

I wanted to thank everyone who took the time to post on this thread. The comments were very helpful. It's important to remember that I posted this topic last year and have worked through the original issues of the cylinder that was pulling less air and the popping above 3200 rpms. You really have to take it back to the mechanical basics of valve adjustment, plugs gapped correctly, dwell and timing set, and ensure that you have no air leaks around the manifolds or in the carbs. I also spent a considerable amount of time setting the floats so the proper amount of fuel was getting to each carb. Ultimately, the 55 idle jets were too small despite some saying they would be fine. I put 60's and it made a 100% improvement. Because I had put so much time into the basics, changing the idle jets made everything easier. Now, I have a consistent idle and there is no hesitation when I rev the engine. I was so thrilled that I drove it for an hour the other evening and the popping was almost gone. I say that because I believe I have an exhaust leak that I need to look into. I pulled the plugs last night and they are not running lean any longer, the plugs are developing a a nice greyish color to them. There are several good write ups on pelican on how to synch and adjust these carbs. One of the most important steps is to balance the airflow between carbs and from side to side at idle and 3000 rpms. After that, the mixture adjustment is easy although I used the Gunson color tune tool. It's a little more time consuming to setup on each cylinder, but easier to adjust in the end. While I feel I'm not an expert on carb tuning, I can diagnose and fix most issues relating to my carbs at this point. Thanks again for the help. I wouldn't have been able to do it without this site and it's members.