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Mon Feb 01, 2010 9:03 pm

I'm trying to identify the source of airleak in my intake (71 vert). The leak is bad enough that I can turn the bypass screw in all the way and the car still idles.

I've checked visually, with carb cleaner, and with WD40 (don't have access to starting spray).

The throttle shaft is ok. The carb manifold gasket is ok. The manifold boots are new and passed the test and the manifold to cylinderhead gaskets are also new and torqued to correct spec.

That leaves the central manifold section. The small heater pipe from the right is discolored and there appears to be a section that was either rusted or drilled/repaired (perhaps to remove carbon block). When I first removed the manifold, this heater pipe did not have a gasket, but a blanking plate inserted where a gasket would be.

I'm wondering if it's possible for a leak into the manifold from this heater pipe. And, if there's a good way to check.

Thx!
BN

Mon Feb 01, 2010 9:29 pm

Use an unlit propane torch. When the engine surges you will have found your leak.

Mon Feb 01, 2010 10:48 pm

never heard of manifold heat leaking into intake.

Tue Feb 02, 2010 3:14 am

How does the car idle overall? If rough, probably an air leak. If smooth, try installing a smaller idle jet.

Tue Feb 02, 2010 6:33 am

I started it cold with throttle stop on second step of cam. It started and idled fine. But after a few min as it warmed up the idled dropped (even though I had not touched the throttle and it was still on the second step of the cam) and then it would pick up again -- on and on it went -- first up then about 10-20 seconds later it would go up. This made testing with a spray difficult as it was hard to tell whether the increase was because of the spray or not.

Also, it bothers me that even with the fuel mix screw out 3+ turns, I can turn the bypass screw all the way in and it still idles.

Sat Mar 20, 2010 12:40 pm

u might have an vacumn on the intake its self mine has one and it was causing the same problem