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Rebuilt my 52 M38 637 because it was running way too rich and rough. Used a good kit from AJP. Rebuild went well - not a complicated carb. Cleaned everything in carb cleaner and blew out passages. Now engine runs great and idles smooth. The Problem: after it sits for an hour or so, it leaks between the main body and the throttle body. Did not do this before the rebuild. Surfaces were well cleaned. Removed the carb, trued the throttle body surface lightly with a file, installed new gasket - still leaks. Removed again and installed 2 gaskets - still leaks always after sitting for an hour or so. No leaks at all when engine is running. After doing some reading, it seems that there should not be fuel in this area of the carb when engine is off. Is this correct? Do I maybe have a check ball problem? Anyone have an idea? Thanks, Sonny

Do you have the correct thick gasket between the carb and the very hot intake manifold?



If you use only a thin gasket the carb will perculate the fuel when you shut down and the manifold heat soaks and it will spill into other areas and may appear as a leak.

Yes, I am using the diffuser with a thin gasket on both sides

Then I would recheck your final assembly piece by piece. Also look very closely for cracks in the bowl adjacent to the venturi opening.

I had trouble with the two diaphragm covers leaking. The covers were slightly warped. I wet sanded them on a flat plate to correct this and the leaks went away. Are yours running down the side a fooling you?. John

Thanks guys - I am going to disassemble it and check everything and check for warpage

Thanks John - you were right. The pump diaphram cover was warped and was leaking. Being on the firewall side, I couldn't see that it was leaking and running down to the main body/throttle body joint where I thought the leak was. Thanks again for the help - Sonny