I installed a brand new Quadrajet Holley on my inline 6. I noticed using the oxygen sensor that the mixture becomes rich suddenly, especially after returning to idle after acceleration. While inspecting the carb, I could see that the fuel level rose above the predetermined level, which caused the mixture to become rich. I tried emptying the bowl and resetting the float level, but after some time, the fuel level will rise above again. The carb is brand new and has been running for about 5 days. The needle is not stuck and is clean, while the float is not sunken. The fuel pump is mechanical, and I don’t think it’s pressure-related since it’s only happening on the primary bowl. Could it be caused by vibration alone? I have a rough idle cam, but I honestly cannot believe a Holley carb would not stand an Isky 525b without issues. These two pictures are 1 minute apart, showing the fuel level rising after adjustment. Any help would be appreciated.
Excessive fuel pressure… you must use a pressure gauge to test it. I have found all kinds of fuel pumps with the wrong internal spring installed creating 7 to 12 PSI from the mechanical fuel pump.
Bao said:
Excessive fuel pressure… you must use a pressure gauge to test it. I have found all kinds of fuel pumps with the wrong internal spring installed creating 7 to 12 PSI from the mechanical fuel pump.
I also install a 1984 Corvette fuel filter before the mechanical fuel pumps like this… then with the power to the coil disconnected, hose to the carb disconnected and into a clean clear plastic soda bottle, get somebody to crank the engine while you observe the pulses into the bottle. Each should be full and equal, not diminishing.
@Bao
Do the 15-second full flow test through the new filter before the pump three times. This is usually enough to clear the sediment from the fuel pump check valves and fuel pump cavity.
Thank you so much. I will check it and I will return here to share the results.
Val said:
Thank you so much. I will check it and I will return here to share the results.
Thank you again. Your answer was very helpful.