fuel pressure question

[Dartgame]

I've been chasing some drive-ability issues with the 52 and am currently looking at the fuel pump and pressure/volume it generates.

 

What I am seeing are fluctuations between 3-4 psi, and then erratic drops to less than 1 psi, sometimes to 2, very random and fairly frequent. I've checked the volume delivery and it seems more than adequate. The gauge I am using is a standard old style vacuum/fuel pressure combo. I was under the impression that the fuel pressure should be fairly stable, but this is not an area I have looked at.

 

Any opinions are appreciated.

[vintage6t]

Just speculation on my part but is the erratic drops due to the needle valve in the carb opening?  Seems like there would be a sudden but temporary drop in pressure when that occurs.

[soth122003]

3-5psi is the pressure most of the flatheads run at, but I think Vintage hit the nail on the head with his answer. 

 

Joe Lee

[Dartgame]

thanks - I had thought about the pressure variation being related to the carb demanding fuel. I noted that it wobbles between 3 and 4 psi consistently, which I figured was the float opening and closing the inlet. The sharper drops seem odd. Higher engine speeds dont seem to change it a heck of a lot, maybe a little more frequent psi variance. When you shut the engine off the pressure reading holds and then falls off very slowly, which is reasonable, probably allowing fuel into the carb slowly as it evaporates through the bowl vents or leaking back through the check valves in the pump itself.

 

I welcome any additional thoughts or comments.

[Dave72dt]

I'd considered the float also when I first saw the topic posted.  I'm more inclined to consider a check valve in the fuel pump not seating consistently.