After getting the C8OF-9510-C carb adjusted and working well after a full rebuild from Drew at afspark, I just started having a problem of fuel being expelled from the secondary vent tube…I didn’t notice any overflow from primary tube / booster. As a result, it floods the engine.
I took the secondary needle and seat out, cleaned, checked o-ring, and reinstalled…fuel still comes out of the secondary vent tube. I then removed the secondary bowl to check the float and didn’t see any issue and reinstalled.
Before trying to restart the engine, I checked the fuel pressure during cranking and its pushing 7 psi. Is 7 psi enough to overpower the needle/seat and flood the engine? The rebuilder’s instructions noted rebuild designed for 5 psi, but in looking at the service manual it showed max of 6.5 psi.
I’m tempted to purchase a regulator to reduce pressure to around 5 psi and recheck. If it still occurs, then need to recheck the needle/seat & float?
Thoughts
Holleys are generally not overly sensitive to PSI assuming clean fuel and a good needle and seat assembly. If instead this was a 4100 I would not be at all surprised to see fuel out of both PRI and SEC vent tubes at that pressure (I’ve been there…).
But 7psi when cranking does seem a high assuming you have a mechanical pump. Makes me wonder what the pump will do at RPM (directly proportional).
In any case, adding a regulator is relatively easy and will help you understand if high fuel PSI is related or not.
After reinstalling the rebuilt carb, it showed 7 psi while engine was running. I’ve driven it approx 15 miles before this issue started. If the fuel pressure was too high, I would assume fuel may come out of the primary vent tube as well?
I’m going to double check the needle/seat and float, and the rebuilder is sending me another set just in case. I’ll probably install an adjustable regulator to verify pressure sensitivity.
Just fought this with my Holley. Only happened during a hot restart. I’m was caused by a saturated nitrophil float. Replaced with a brass float and problem corrected
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Glad you found the cause. Mine has occurred both times during cold start over past week.
It was aggravating today as I was headed out to a cars n coffee event with friends, but was stopped due to the flooding. Of course I’m the only one with a non-GM car and had to endure the friendly banter.
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