Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

Fuel Pressure

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von:
  Is it possible for a stock mechanical fuel pump (small block Chevy) to have too much pressure and overcome a Q jet needle and seat (.120)? If so, how common?

Cliff Ruggles:
Yes, there are quite a few mechanical fuel pumps showing up these days that have WAY too much pressure for any carburetor......Cliff

von:
Cliff, I shipped you the problem carb Friday that I talked to you about on the phone Thursday (gasket seepage/slow flooding problem after shut off). I'm wondering now if the fuel pressure could be too high from the stock pump and overcoming the needle and seat after the engine is shut off, causing the fuel level to slowly rise. The fuel pump has been on for years and quite a few miles so if that's the problem it would likely be something that happened in the pump recently.

Cliff Ruggles:
If the carb passes pressure, vacuum and running tests, then look elsewhere for the problem(s).  Could be high fuel pressure, a gauge in line is the best way to determine if this is happening?.....Cliff

von:
I installed an in-line fuel pressure gauge near the carb. when the engine is running it swings wildly and rapidly (probably with every pulse of the pump) from about 3 to 12 psi. When the engine is shut off it stays at 8.5 psi then very slowly bleeds down to 0. A second q jet on this engine is also getting the gasket so wet after a few hours it runs down the front of the carb.

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