Vacuum leak at Intake Manifold

[busadick]

Still trying to get my 1600 dual port with dual Solex 32/34 PDSI carbs to idle correctly. Motor will start, but at cold idle, the 3/4 cylinders are not firing (idles great when warmed up). I get shaking and a lot of smoke until it warms up (about 5 minutes). After that the motor runs fine.

I suspect a vacuum leak at the manifold. When running, if I spray carb cleaner where the cast iron manifold bolts to the head, the motor slows down. This happens on both heads. I replaced the thin metal gasket under the manifold and retightened the manifold bolts on the 3/4 head, but the suspected vacuum leak is still there.

Are there any better gaskets to use there than the thin metal ones? Anyone else have this problem and corrected it? Any comments are greatly appeciated!

[The Noof]

The metal gaskets are the best.Just make sure everything is clean and straight.Check the sleeves too.

[glutamodo]

Also, you said you replaced the metal gaskets so I'm guessing they were new, but examine those before you install them to be sure they've never been "crushed" before, or damaged in the raised "crush" area, becuase once that has been compressed, you cannot trust to be able to be "crushed" again and seal. Those are one-use-only gaskets.
-Andy

[busadick]

Thank you Noof and Glutamondo for your replys. So the metal gaskets are the ones to use. I did use a new one, and tightened the manifold nuts as tight as I could (without stripping), but I still suspect a vacuum leak beacuse when I sprayed Gumout carb cleaner at the base of the manifold the engine slowed down noticeably. Now the #3 cylinder still doesn't fire at cold idle (but the #4 does WTF!).

The gasket did not fit well over the studs. I had to push down hard on the gasket to get it to seat. Could I have bent the gasket? If so wouldn't the cast iron manifold have seated (crushed) the gasket properly after tightening the nuts?

I am at a loss as to what to do next. Any suggestions?

[sturgeongeneral]

[busadick]

So I replaced the metal crush gasket between head and manifold again. Bus still would not idle due to misfiring on the 3/4 side. My friend and VW guru Bob Ellis suggested synchronizing the carbs, and even lent me his cool vintage Moto-Meter carb synch tool.

I adjusted the linkeage on the 3/4 side so both carbs would open the throttle at exactly the same time (linkage was loose on the 3/4 side), synchronized the carbs (the 3/4 side was not flowing air as much as the 1/2 side), adjusted the choke (choke was staying closed longer on the 3/4 side) and now the idle is smooth, no more smoking or shaking, and the engine runs great!

Bottom line, it was a carb synch problem!

[seajay96]

does it still have a noticeable change in rpm when you spray carb cleaner at the base of the intake? you may have corrected your primary problem but could still have vacuum leaks that will cause you to run lean...

[busadick]

Yes, the intake manifold leak was still there after I used the new metal gasket. I have now switched to the thick fiber gaskets (trimmed by using the metal gasket as a template), and the manifold leak is gone!

I have heard that for a single carb the metal gaskets are fine, but for dual carbs, the fiber gaskets are best. Now I'm a believer.

The saga did not end there. I was still getting a rough idle, better than before, but still not right. The soulution came after a 200 mile road trip to Lansing for the Potter Park Zoo VW show. Bus ran fine on the way there but about half way back the engine began to misfire severely. Pulled over and checked the chokes, both were open and working. Limped home, and the next day pulled the plugs. Found the #4 plug had the electrodes smashed together, almost no gap, and black with carbon. All other plugs were good.

How did that happen? What could cause the plug to look like someone had hit it with a hammer and smashed the electrode down?

Don't know. Anyhow, changed the bad plug, now engine runs smooth. Idle is perfect as is highway performance. All's well that ends well!

[Towel Rail]

Sure it was the right kind of spark plug? I'm visualizing a too-long spark plug reaching in far enough to get smacked by the piston...
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[busadick]

Spark plugs are Bosch W8A. I have never seen a plug look like the one that came out. Plug was new, too!

I don't think I was careless enough to damage the plug upon installation. I remember gapping all four prior to installation. This was the cylinder that was misfiring while I was sorting out all the other issues I had with these carbs (see my earlier posts above).

[Das Dragon]

Could something have dropped down the carb and into the combustion chamber to damage the plug then got passed out the exhaust?
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[busadick]

Someting fell inside the cylinder and is rattling around in there. I suspected my stock exhaust was rattling, so I ordered a header/single quiet pack from Busboys. Sure enough, the stock exhaust must have loose baffles because when you shake it it rattles like a tin can full of rocks.

My header came in, I was dissapointed to see it was an EMPI unit from China! I installed it, but I had to bash one corner down so it would clear the bumper. Still there is a loud rattle from cylinder #4. I stuck a flexible-tip magnet into the cylinder thru the spark plug hole to see if I could fish out what ever was in there, but nothing came out.

Now I will have to pull the engine and head.

The saga continues....

[volksterii]

Sounds like maybe you broke a valve and it is rattling around in there. I assume that you put another plug in and ran it and it still rattled and still had a miss or something?
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