The Stovebolt Site Forums The Shop Area Engine Shop Intake gaskets

Newly rebuilt 261 Chev with 235 head with stock intake, single barrel Rochester carb was running great until a 220 klm (100 mile) drive to break in the engine. I went with two others to a cruise both Fo@#’s1 was a 32 1/4 ton PU with triple carb flathead and a 61 Fairlane 289 v8 neither could leave me behind it was very strong.

Suspect that I developed a vacuum leak, it runs very rough at idle and smooths out and has a significant rpm increase if you cover the carb with either your hand or even reinstalling the oil bath air cleaner.
Vacuum gauge now reads 14 to 17 with small needle movement it was 18 to 19 with steady needle.
I will be doing a vacuum check tomorrow with a propane torch or maybe starting fluid.
Question for the day.
Is it a good idea to have gaskets above and below the phenolic plate or none at all?

From personal experience, I use a gasket below the phenolic spacer and above. When the carb was installed without the one on the manifold, I had a vacuum leak.

To check for vacuum leaks, take a propane torch and turn on it on without lighting it.

With the engine idling, move the torch around any possible vacuum leak areas like the carb mounts, bowl and base connection, wiper connection, intake manifold connections, etc. If the engine rpm changes at any time, you'll know that you've found your leak.

Covering the carb with your hand is like pulling out the choke. The engine runs richer. That's not necessarily an indication of a vacuum leak.

Doyle, If you find you have a vacuum leak (and you may not) and the leak turns out to be where the manifold attaches to the head, here's an option for you (compliments of Evan / Coilover who is sadly no longer with us): Use the high temperature silicone sealant rather than any of the overpriced "specialty" gaskets. It is red in color and I saw some made by J-B Weld that had a higher temp rating. He showed me a straight 8 he had done this on and said it had over 25,000 miles with no leaks nor problems. He said what he did was to apply a ring about 2mm to 1/8inch in diameter about 1/4 inch from the inner edge of both sides of the metal gaskets, let it cure until it barely had a skin and then bolt the intake manifold on. I have not found there to be too many leaks at the phenolic spacer. Almost all these throttle bodies were cast iron and it usually doesn't deform. Good luck!