[C2] Carb issues
Thread Starter
Drifting
Joined: Dec 2014
Posts: 1,761
Likes: 138
From: Chantilly Virginia
Carb issues
1966 L79, Holley 4160My carb is draining the primary fuel bowl very rapidly when not running. Even overnight, it requires a lot of cranking to get it to fire, usually with backfire through the carb. I can add some fuel through vent tube and it starts without excessive cranking. I tried the test for a blown power valve, putting my finger over the vent tube for the primary bowl while idling. It does not stall the engine at all – keeps idling. Plugs look like an overly rich condition, dark insulator, carbon. Areas to check?
Thanks,
Ralph
Thanks,
Ralph
Race Director
Joined: Apr 2005
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From: Bowling Green, Kentucky
Where is the fuel going?? Onto the intake manifold external runner areas, or into the intake itself and perhaps the cylinders?? I would pull the carb and check for gas liquid pools in the intake under the carb.
You may have an internal leak from fuel bowl thru carb into engine.
I had a similar issue and eliminated it by rebuilding the carb. Had a few leaking gaskets, and one or two plugged small vent holes in the carb as best I could tell. Rebuild fixed everything for about one year. Now I have slight leakage onto intake manifold runner areas (external) and will try re-gasketing and tightening the body screws again. If that doesn't fix it, then surfaces are likely warped, and need machining.
Larry
You may have an internal leak from fuel bowl thru carb into engine.
I had a similar issue and eliminated it by rebuilding the carb. Had a few leaking gaskets, and one or two plugged small vent holes in the carb as best I could tell. Rebuild fixed everything for about one year. Now I have slight leakage onto intake manifold runner areas (external) and will try re-gasketing and tightening the body screws again. If that doesn't fix it, then surfaces are likely warped, and need machining.
Larry
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From: Central Arkansas
However some carbs do not use a check ball - my 3247 doesn’t. I think you have to look carefully at the seat where a check ball would go to see if it has 4 tiny radial grooves. If grooves then it should have a check ball. If no grooves then no check ball (from memory).
I suspect just today’s fuel evaporation out of the bowls but if it is somehow leaking down into the engine, the throttle blades and plenum should appear wet several hours after shut down.
I suspect just today’s fuel evaporation out of the bowls but if it is somehow leaking down into the engine, the throttle blades and plenum should appear wet several hours after shut down.
Safety Car
Joined: Mar 2009
Posts: 4,191
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From: Corpus Christi, TX
Interesting. My 3310 has a small cylinder with a cone shaped bottom end that drops into the flow bore in the main carb body. Didn't realize some Holley designs didn't have a check valve.
Race Director
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From: Central Arkansas
Quick question on Holley secondary diaphragm check ball - CorvetteForum - Chevrolet Corvette Forum Discussion
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Safety Car
Joined: Mar 2009
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From: Corpus Christi, TX
Dan, I think we're hijacking this thread .. lol
We may be thinking of different things. The check valve the OP should look for is underneath the accelerator pump squirter. It drops in before the squirter gets screwed in place. If thats left off, fuel can siphon through the pump squirter. It will drain the bowl dry.
There are ball type check valves for the pump squirter. Newer ones look like that little pointed cylinder.
Scroll down to pic #9 at the link.
https://www.holley.com/blog/post/acc...y_carburetors/
We may be thinking of different things. The check valve the OP should look for is underneath the accelerator pump squirter. It drops in before the squirter gets screwed in place. If thats left off, fuel can siphon through the pump squirter. It will drain the bowl dry.
There are ball type check valves for the pump squirter. Newer ones look like that little pointed cylinder.
Scroll down to pic #9 at the link.
https://www.holley.com/blog/post/acc...y_carburetors/
Race Director
Joined: Jan 2003
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From: Central Arkansas
Yeah, your right Avispa - my fault - looks like I mis-read your post - different check ball. I don’t know that an accelerator pump can drain into the throat anyway. It has quite a lift up to the shooter it would have to siphon over. I’ve had them get hot from the manifold and push fuel out the squirter after a heat soak.
I’ve just not had an issue with a Holley leaking internally - I guess it can and does happen with a warped metering body but I would think it would leak externally too. But, as suggested, carefully removing the carb and examining the plenum for wetness is the surest check.
I’ve just not had an issue with a Holley leaking internally - I guess it can and does happen with a warped metering body but I would think it would leak externally too. But, as suggested, carefully removing the carb and examining the plenum for wetness is the surest check.
Last edited by DansYellow66; Apr 11, 2021 at 07:21 PM.
