Fuel pressure drop

Jim_Ferrell · #1 (**permalink**) 10-09-2007, 12:03 PM

I am using a Holley fuel pump, regulator, and 750 carb. I have the fuel pressure set for 7 pounds when running and every thing is cold. As the under hood temperature goes up, my fuel pressure goes down to almost zero.

Twice (after it was hot) I had a hard time starting it until I let the fuel pump run for 20 seconds before starting. Once running, it seems to get enough fuel but I am worried about running lean.

I can dial up the pressure when hot but it is too high when cold; I am worried about flooding the carb and hydro-lock.

I put an ice bag on the regulator between sessions yesterday at Autobahn and the pressure comes up. I also added gas to the tank at lunch and noticed a big jump in pressure; I guess the gas in the buried tank is 60 degrees and that cooled my tank, and provided in line cooling to the regulator.

The regulator and canister filter are mounted forward of the engine on the passenger side frame at the control arms mount point. I have thermal wrap on the stainless fuel lines but not on the canister or the regulator. The pump is mounted below the gas tank on the rear frame rail.

Thoughts?

Jim

Jerry Clayton · #2 (**permalink**) 10-09-2007, 01:12 PM

change the regulator---call Corey for a part number--630-365-6737

Jerry

lineslinger · #3 (**permalink**) 10-09-2007, 01:38 PM

What Jerry said, and maybe think about relocating it or adding a heat shield. From your description it sounds like there is a lot of header heat affecting it?

scootter · #4 (**permalink**) 10-09-2007, 05:10 PM

Sure the pressure gauge is good? Is it a liquid filled gauge?

Scott

Jim_Ferrell · #5 (**permalink**) 10-09-2007, 06:30 PM

Quote:

Originally Posted by lineslinger

What Jerry said, and maybe think about relocating it or adding a heat shield. From your description it sounds like there is a lot of header heat affecting it?

It is well forward of the header, 12 inches or so.

Jim

Jim_Ferrell · #6 (**permalink**) 10-09-2007, 06:32 PM

Quote:

Originally Posted by scootter

Sure the pressure gauge is good? Is it a liquid filled gauge?

Scott

Installed a new liquid filled gauge. Same result.

Jim

Jim_Ferrell · #7 (**permalink**) 10-09-2007, 06:33 PM

Quote:

Originally Posted by Jerry Clayton

change the regulator---call Corey for a part number--630-365-6737

Jerry

Thanks, I will.

Jim

bermblaster41 · #8 (**permalink**) 10-09-2007, 07:09 PM

Jim I feel your pain. Go to small block forum and check out my thread on fuel pressure fluxuation. Definatley ditch the liquid filled guage and get dry guage from summit for 15.00 Hope this helps. Bermblaster Fuel pressure fluxuation problems

Jim_Ferrell · #9 (**permalink**) 10-27-2007, 08:32 AM

Quote:

Originally Posted by bermblaster41

Jim I feel your pain. Go to small block forum and check out my thread on fuel pressure fluxuation. Definatley ditch the liquid filled guage and get dry guage from summit for 15.00 Hope this helps. Bermblaster Fuel pressure fluxuation problems

Thanks. At long last I received an answer from Holley; it confirms your experience; liquid filled gauges are affected by heat soak. My plan now is to install a sender in the second port of my regulator and monitor it with my VOM.

Jim

Jerry Clayton · #10 (**permalink**) 10-27-2007, 08:38 AM

Jim---I always used an electric guage on my pro/stocker

But also---a guage doesn't cause pressure problems

Jerry

ALSNAKE · #11 (**permalink**) 10-27-2007, 11:29 PM

Jim, hard starting after hot is caused by gas ---we have winter blend gas in our area, starts the end of september and goes untill around the begining of april ---- after restart would run rough for about a 1/4 mile then fine, cool fuel to the carb - all fine untill the next stop
I had/have the same gauge problem only with winter gas, during the summer fuel pressure reads fine even on the hottest days - I believe the gas line is getting just hot enough for the fuel to turn to gas (bubble) causing inaccurate readings especially at idle for a few min. mine would drop to about 1 psi drive for a couple mile and check gauge and fine 6-7psi ---------

Hard start after hot, fuel is boiling out (easier vaporization at lower temp of the winter blend)
Adding race gas 2-3 gal per tank($$$) seems to stop the hard starts or turn off the electric fuel pump about 30 sec before stopping motor(hard to get into the habit to do this) or just remeber the car is flooded for hot restarts untill spring

Oh, generally only a problem on carberated cars Fuel injected usally no problem --fuel pressure 6-9psi carb to 30+psi injected

Al

jeffko · #12 (**permalink**) 11-04-2007, 07:56 PM

Jim, seems like the regulator is being over worked and can not keep a reliable setting due to other variables. No doubt change it and this is not a part to save money on.