The Ford Barn

PC/SR · 04-29-2019, 06:43 PM

I am running dual Holley 94s (on a Model A 4 banger) which call for 3 psi fuel pressure. Have a Napa 4-7 psi elec fuel pump, and a Holley 804 1-4 psi regulator. Factory adjusted to 2.8 psi. On a cold start it measures 2.8-3 psi. Question is, as the car warms up, at idle or otherwise, the fuel pressure slowly drops to around 1 psi.
Originally had a Napa 1-4 psi pump without a regulator, and at the pressure gauage near the carbs it was 3 psi. Same thing, as it warmed up, psi slowly decreased, to zero with this lower psi pump.

I know pressure will drop some as the float valves open. But it does this at idle, when there should not be a problem keeping up with fuel usage, and also when running. Any ideas?
PS--Did change pressure gauges and readings the same. Thanks

34PKUP · 04-29-2019, 08:07 PM

I was always under the impression that so long as the pressure did not over power the float and cause over filling/flooding of the float chamber the pressure could be even 1/2 psi so long as the volume provided enough fuel to keep the chamber at proper level.

37 Cab · 04-29-2019, 08:23 PM

What gauge are you using? The liquid filled ones will read less pressure when they get hot as they are not vented and as the liquid heats up it acts against the pressure in the gauge internals.

PC/SR · 04-29-2019, 11:06 PM

37-Thanks both were liquid filled. Will try a plain one.

JSeery · 04-30-2019, 09:04 AM

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There have been several threads on the HAMB on having to drill a hole in the gauge to get it to work correctly. Don't remember the size or location.

04-29-2019, 06:43 PM	#1
PC/SR Senior Member Join Date: May 2010 Location: Santa Rosa, CA Posts: 1,278	Fuel Pressure question I am running dual Holley 94s (on a Model A 4 banger) which call for 3 psi fuel pressure. Have a Napa 4-7 psi elec fuel pump, and a Holley 804 1-4 psi regulator. Factory adjusted to 2.8 psi. On a cold start it measures 2.8-3 psi. Question is, as the car warms up, at idle or otherwise, the fuel pressure slowly drops to around 1 psi. Originally had a Napa 1-4 psi pump without a regulator, and at the pressure gauage near the carbs it was 3 psi. Same thing, as it warmed up, psi slowly decreased, to zero with this lower psi pump. I know pressure will drop some as the float valves open. But it does this at idle, when there should not be a problem keeping up with fuel usage, and also when running. Any ideas? PS--Did change pressure gauges and readings the same. Thanks

04-29-2019, 08:07 PM	#2
34PKUP Senior Member Join Date: Feb 2011 Posts: 794	Re: Fuel Pressure question I was always under the impression that so long as the pressure did not over power the float and cause over filling/flooding of the float chamber the pressure could be even 1/2 psi so long as the volume provided enough fuel to keep the chamber at proper level. Last edited by 34PKUP; 04-29-2019 at 08:14 PM.

04-29-2019, 08:23 PM	#3
37 Cab Senior Member Join Date: Dec 2014 Location: Miami Oklahoma Posts: 535	Re: Fuel Pressure question What gauge are you using? The liquid filled ones will read less pressure when they get hot as they are not vented and as the liquid heats up it acts against the pressure in the gauge internals. __________________ Tommy

04-29-2019, 11:06 PM	#4
PC/SR Senior Member Join Date: May 2010 Location: Santa Rosa, CA Posts: 1,278	Re: Fuel Pressure question 37-Thanks both were liquid filled. Will try a plain one.

04-30-2019, 09:04 AM	#5
JSeery Member Emeritus Join Date: Nov 2012 Location: Wichita KS Posts: 16,132	Re: Fuel Pressure question Sponsored Links (Register now to hide all advertisements) There have been several threads on the HAMB on having to drill a hole in the gauge to get it to work correctly. Don't remember the size or location.