Fuel Pressure Varies

blue72Member

Took 4507 on the first drive in 20 years over the weekend! It ran great, with one exeption. I pulled upto a stopsign, it stalled out and wouldnt start. Engine temp was around 190-200 degrees. Fuel pressure gauge showed 0 psi. Unusual for her not to start right up. Typically, I give her one pump, and its instant when i turn key. Acted as if it was flooded, but not with 0 psi and no smell of fuel...i dont see how it could acutally have flooded. To start it, I eneded up holding her at WOT. She fired up and got me home with no problems. Back home In the drive way...idling, it was showing 0-1psi.
The following day after it cooled down overnight I started her, went right to 6-7psi, after i drove a few miles the pressure was down to 1-2. never stalled though.

Could this be a fuel pump issue? Vapor lock? Heat soak... any ideas....or remedies? I thought that a mechanical fuel pump either worked or it didnt.

Brand new Components that have just been installed:
Fuel cell - which is properly vented
Braided stainless fuel lines
Fuel filter
Fuel Log
Fuel pressure guage
Holley 750 carb
1" Phenolic carb spacer

The fuel pressure gauge is liquid filled. I do recall hearing something about liquid filled gauges and pressure reading. Can anyone add insight?

(only fuel system component that isnt brand new is the Holly mechanical fuel pump)

9/10/125:16 AM

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marlinjackThe Machinist #5723 AMARGOSA MACHINE 'Running on Empty- Middle of Nowhere'

...I bet You the 20 Plus Year Old Mech. Fuel Pump, has a Ruptured Diaphram!! You will also be mixing oil with the fuel and smoking out of the Exhaust AND there would be Gasoline in the Oil and Pan! Very Dangerous!!

...I once used a Holley Mech pump! The Chrome One! Left me stranded when one of the two internal check valves, popped out of it's counterbore.
I went to a Electric Holley Pump, the red low pressure one. Have had No problems since and has run a Solid 6 PSIG...

The only other reason for Fluctuating Fuel Pressure..would be a 'Waterlogged' Float! Float doesn't float, needle stays open/off the seat, fuel is pumped through the Carb, flooding the Engine..AND! The gauge Never reads above Zero - 1, because the Flow is never restricted! The 'Head' of Pressure is Never Built Up!! Pressure is only produced when a flow of liquid is Restricted. Pumps DO NOT Produce Pressure!! They Produce a Flow!! There are NO 'High Pressure' Pumps! They are 'High-Flow'-'High Volume', Pumps!

There is also the Chance of a Blown 'Power Valve'!! That Will produce the same symtoms!! I have come across this more than once in My lifetime!...

9/10/121:43 PM

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George PAdmin.

I read your blurb saying the fuel tank is properly vented, but it sounds to me as though the fuel tank is not vented well; as the fuel pump draws fuel from the tank a vacuum is building up inside the tank. Remove the gas cap & drive it around for a few minutes, see if the problem goes away. Its a simple test that couldn't hurt to try.

-G

9/10/122:44 PM

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noquarterMember

Most of your post points to lack of fuel. But if it started with pedal at WOT, that's usually an indication of a flooded carb, clearing itself and not pulling more fuel in, because the vacuum at WOT/idle almost only pulls air. Could the 0 PSI be because the float needles were dirty/stuck open (no back pressure), flooding the carb? Dirt in the needles is not unlikely if driven for the first time in years. The gauge will only show pressure if a pump creates pressure in a closed system, if the hose fell of for instance, your gauge would immediately read much lower.

Just a guess from a continent away...

9/11/1212:21 PM

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