Question: Chevrolet Caprice Carburetor
Hello. I have a 1977 Chevrolet Caprice that my father purchased new. I learned to drive at 14 in this car and subsequently purchased it from my dad about 10 years ago as a "spare" car. Two years ago I replaced the engine with a new 350 cid GM crate motor.
Before installing I removed the stock cam and installed an Edelbrock Performer manifold and camshaft. After a few months, I began having problems with the stock Quadrajet (vacuum break diaphragm leaking) and replaced it with an Edelbrock 600 CFM with electric choke. The old Quadrajet had a choke stove that was heated by the exhaust gas from a port in the intake manifold. The opening in the manifold was sealed off (with the bolt on aluminum cover) when the Edelbrock carburetor was installed.
A new problem developed with the Edelbrock carburetor installed, the carburetor will flood the engine after a few minutes (5-10) after the warm engine is shut off (not every time though). The carburetor has been rebuilt, the floats adjusted correctly, and the stock fuel pump has been replaced with another stock fuel pump (about 6 psi). The issue still remains. Note that the engine does not run hot, usually 180F (has a 160 thermostat).
While running, the car runs great and the carburetor is tuned very well, I have worked with these carburetors for 15+ years. There are never any flooding issues when the car is running, no matter how hot it is.
My question is, do you think the fact that the intake gaskets with the open crossover still installed is causing the problem? I'm wondering if the heat is coming up from the hot exhaust after the engine is shut off and heating up the carburetor to the point of causing it to flood? If so, do you think changing to new intake gaskets that would block the crossover would solve this problem?
Also note that I have the heat riser valve forced in the open position, so that is not the issue. I had issues getting the intake on without the rear seal leaking, so I don't want to pull it off and risk another leak if I don't need to. The strange thing is that I never had any flooding issues with the Quadrajet, so I am not sure if this will solve the problem or if there could be some other issue with the carburetor?
Any help is appreciated.
Best regards,
Stuart Paterson
Answer:
I think that the carburetor itself is bad. I have seen many times new and reconditioned carburetors fresh out of the box are bad. And rebuilding them works only a small percentage of the time. I have rebuilt a few hundred carburetors in my career and I would estimate they came out good only about 30% of the time. Also, carburetor rebuild kits aren't what they used to be either. Kits today come with barely enough new parts and gaskets to do the job. Years ago the rebuild kits came with almost all the new parts and gaskets that was on the original.
It's possible the heat from the manifold is causing the fuel in the carburetor fuel bowl to percolate and flood the engine. If that is the case then replacing the intake manifold gaskets would solve the problem. Before doing that I would use an infra-red thermometer to measure the temperature of the carburetor and see if there is a significant rise in temperature. If there is and it starts to flood, you will know for sure that is the problem. On the other hand if there is no significant rise then you can be pretty sure it's a bad carburetor.
