Cold cranking vacuum reading.

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Jul 18, 2005 | 07:05 PM

Pinkster1

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Cold cranking vacuum reading.

302 marine engine, Stock fresh rebuild. won't idle below 1200rpm unless I squirt a little extra gas and I can get it down to 700rpm.

So either carb issue or serious vac leak.

I have taken the Holley 2300c apart several times after I gave it a fresh rebuild, and everything checks out. I've tested for vac leaks while running engine@1200rpm
by spraying carb cleaner around base, head interface and back and front of manifold and no rpm increase. When engine is warmed up, valve covers will breath vapors, so I don't think there is an internal leak. Plus I have 7psi fuel while cranking and float is set correctly.

What I did was, take a piece of Lexan and place it over intake with some vac grease, and got a cranking vac reading off the PCV port of 14"-15" for a cold, not broke-in engine, So I assume that's pretty tight. I then put the carb on, back off the throttle stop so blades are closed, and turned the idle jets in. Cranking vac was 5"-7"

So I'm loosing ~7" vac with carb. There are only two ports under the blades and there on the base. One feeds the choke and the other I think is dead.
The throttle shafts seem relatively tight. base gaskets fit correctly.

Any ideas?

Thanks

Last edited by Pinkster1; Jul 18, 2005 at 07:10 PM.