Too much fuel pressure

E

El Rat

Senior Member
Hi gents...
I am getting near the finish line with my AB powered 38 Ford coupe'. Much to my suprise it seems that my stock (rebuilt) fuel pump makes 6 to 7 pounds of fuel pressure @ idle. Seems like there are three or so options:
  • replace the diaphram with a wimpy one
  • Add shim stock and extra gasket to pump base seal
  • Grind .060 or so off of the end of the FP rod
What say you'all? ty g
 
El Rat said:
Hi gents...
I am getting near the finish line with my AB powered 38 Ford coupe'. Much to my suprise it seems that my stock (rebuilt) fuel pump makes 6 to 7 pounds of fuel pressure @ idle. Seems like there are three or so options:
  • replace the diaphram with a wimpy one
  • Add shim stock and extra gasket to pump base seal
  • Grind .060 or so off of the end of the FP rod
What say you'all? ty g
Click to expand...

Is your gauge accurate down in that low range? I would run it a while and see if the engine floods. If the pressure is to high the needle valve will leak and the engine will run rich. If to much gas is leaking it will get in the oil. When the fuel pump gets hot the pressure will drop. G.M.
 
The best way to get the pressure down if the pump makes too much is the change or adjust the diaphragm spring,this is what governs the fuel pressure,
look in the ford service books,it gives the info on the different springs for different models,length and force etc.

Lawrie
 
Lawrie has it...current stock pumps seem to frequently come with some generic spring meant for use with maybe SBC with modern carb...
Get your old pump out of the trash can, swap its spring into the new one.
 
Thanks all
Yep it's leaking one carb of two. I increased the pressure on the needle and it helped for a short while. However I think 6 to 7 pounds is too much.
I have an electric pump and regulator at the tank. It is set @ 3#'s and the gauge at the fuel block says 2.5#'s...engine not running. Never thought about cutting the spring or replacing it with one from the old diaphram. Thanks all, g
 
this is the info from the ford service manual.
Lawrie
 

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don't mess with the rod, if needed put thicker shims under pump stand, if the pump is from china I will bet its putting out 7 to 9# of pressure, almost 3 time more than the float can handle
 
El Rat said:
Thanks all
... I increased the pressure on the needle and it helped for a short while. ...g
Click to expand...

What kind of carburetor are you running that has a pressure adjustment on the needle? It's either open or closed, actuated by the position of the float.
 
El Rat said:
48's
Bend the tab puts more pressure on the needle as the float sinks. g
Click to expand...
That would increase the pressure on the seat, but it will also change the fuel level in the bowl. Fuel level needs to be at a proper level and is one of the settings when setting up a carburetor, so don't think just bending it to increase seat pressure is a good idea.
 
El Rat said:
48's
Bend the tab puts more pressure on the needle as the float sinks. g
Click to expand...

All the tab does is control at what fuel level the needle closes off the fuel supply - the pressure is strictly driven by the design of the float and the fluid type it sits in.

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Many of the new/repop fuel pumps have WAY too much pressure and will cause almost all these older carbs to leak. You really need to have a constant pressure of only 1.5 to 2.0 lbs . . . more than that, you're asking for leaks and all the problems that come with them.

The idea of changing the spring makes the most sense.

Dale
 
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