Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

Excessive fuel pump pressure

what ill effects would be caused by too much fuel pressure in a carburated engine(normal pressure6 psi but the fuel pump was putting out 13 psi)

Flooding would be the primary result. Continued operation under those conditions could result in cylinder wall scoring due to the lubricating oil film being washed down by excessive gasoline. If your pump puts out 13 psi, you really need to install a bypass/return regulator.

The fuel level in the carburator bowl will be a little higher because the float will have to develop more pressure to balance the increased pressure on the inlet needle valve. If the needle valve is marginal and leaking, there will be fuel slopping over from the main nozzle at idle and on shut down. As stated previously, that can flood the engine on a hot restart and dilute the oil with gasoline over time. If the fuel bowl level does not rise high enough to overflow the main nozzle, the carb will just run a little richer than it would at the lower pressure. Having the main nozzle active while idling will cause erratic idle, a tendency to load up, which has to be cleared by reving the engine.

If you have a performance carburator, you might check with the carb manufacturer to see what their experience has been. There is an adjustable pressure regulator to drop the pressure at the carburator to the specified amount.

researcher…your response accurately describes what i experienced-the carb. was then then taken apart and i found that the primary needle valve had a groove in the seat-could the 13 lb. fuel pressure have been the cause of this groove???the engine had been run 400 freeway miles with this fuel pressure when this happened-the fuel system is well filtered and the carb. was clean inside…much thanks for your response

Yes, the excess pressure required by the float to close the inlet needle valve against the high line pressure will cause a groove on the vitron part of the needle. When you shut off the engine, the higher fuel bowl level will press the needle into the seat harder. If even a microscopic particle got between the seat and needle the leakage at low power output would again raise the bowl level causing high pressure on the vitron part and idle/low speed problems. If the needle valve was not recently renewed, it is possible that previous wear and hardening of the tip made the situation worse.

Thanks for getting back.