Mechanical fuel pump pressure question

[Duckhnter83]

Should a mechanical fuel pump hold pressure after you shut key off? Also I have noticed my pump puts out 7psi but it can warm up and sometimes drop down to 3 psi. What could be the culprit?

[Lizardracing]

Depends. Pressure is a restriction to flow so if the valves in the pump and the valve...er...needle and seat are good AND the float level is high enough to keep it shut than yeah, It will hold some pressure.

Valve in the pump aren't perfect and might leak, possibly just debrii under one of them. The gaskets in the carb might leak too, especially into the intake where it's hard to see or notice. If it's starts easily and runs well I wouldn't think twice about it as all of them will leak down eventually. Maybe over a few minutes or an hour.

Pressure lose when hot.....Could be the pump valve, float levels, or the floats sinking or something along that lines. It could also be an air leak somewhere in the fuel line or a connection affected by heat. A distant possibly could be the cell vent or even plugged filter. Have you verified your gauge is working accurately? Nothing sucks more than chasing something you assumed was working.

[usafracer]

Dropping pressure after running tells me you have a restriction on the suction side.