adjusting fuel pump pressure

TomM · Post by **TomM** » Fri Jan 22, 2010 6:09 pm

Has anyone successfully reduced the output pressure from an M38 fuel pump?
Mine was rebuilt by one of the vendors and runs 7.5 psi out. The carb is spec'd for somewhere 2.5-4 (from memory).
In theory the screws can be loosened and some slack put in the diaphram but has anyone actually done this?

I have some flooding problems which may be vacuum leaks from the manifold to block gasket or may be excess fuel pump pressure.

Tom

dod03-52 · Post by **dod03-52** » Fri Jan 22, 2010 8:31 pm

Do you have the "mounting base spacer" between the pump and the block? It is about !/2 inch thick, it lowers the pressure by less action of the diaphram arm on the cam.

TomM · Post by **TomM** » Fri Jan 22, 2010 9:21 pm

Yes,
Spacer, gaskets and original long bolts are installed.

TM

Stir-stick · Post by **Stir-stick** » Fri Jan 22, 2010 9:36 pm

Did you rebuild the pump ? The diaphram is supposed to be in the down position when tightening the screws.Someone correct me if I'm wrong. I'll double check. Stick

Post by **wesk** » Fri Jan 22, 2010 10:34 pm

Yes, if the pump rocker arm is not fully depressed when tightening the body screws the pump pressure will be too high.

Tom,
You should remove the pump and loosen the fuel body screws then fully depress the pump and retighten the screws. That should do it.

TomM · Post by **TomM** » Sat Jan 23, 2010 8:18 pm

Got it,

I should be able to get to it this week and will post results.

Thanks

Tom