fuel pressure creep.

[dwelch]

this issue probably been covered about a million times but just seemed to pop up to me lately. i run a carter mech. pump (not sure which one) and a edlebrock 1904 q-jet on my 350 sb with cliff's kit in it. i have had this carb on a couple engines over the years without any problems. had some time on my hands so i hooked up a gauge just to verify everything was operating as it should. fuel pressure was about 5.5 when cruising and started to creep up to about 9.5 a idle. what seemed strange to me is that this combo runs great. it seems to be right on the money all the time. i know  the old saying "if it's not broke don't fix it" but i would feel better if everything was 5.5 all the time. hard to read plugs with all the additives in the fuel but they all look great with a light tan on them. don't know the age of the pump. this high pressure at idle does not seem to hurt performance. maybe it could be the good needle and seat and float in cliff's kits, just don't know. any thoughts?   Denny

[Cliff Ruggles]

I've seen a few set-ups "creep" when "dead headed" or no return system used. 

Many years ago I purchased a Carter 120gph "high performance" mechanical pump.  For the most part it worked OK, but on occasion I'd get some minor flooding issues when hard on the brakes or sitting for a while at a stoplight.

I decided to do a pressure check, and it showed around 7-8 psi but would "creep" up to 12psi or even higher on occasion.  I ditched that pump, went to an electric pump with a regulator and full return system, and never looked back. 

All that happened in the later 1990's and the mechanical pump was marginal for the power level right to start with as I was also having issues with hard runs at the track running the bowl low.

That problem also disappeared with the fuel system improvements and I went on to sump the tank, move the electric pump behind the tank (Comp 140), and 8AN lines/fittings everyplace with a return system.

Best thing I ever did for my car and that system is still in place today and works flawlessly.  In all these years I've replaced the pump once and put brushes in it and on the shelf for a spare......Cliff

[tayto]

Cliff, what about using a regulator like this one:
[url]https://www.summitracing.com/int/parts/sum-g3032/overview//url]

with a higher PSI mechanical pump?

[Cliff Ruggles]

I use the same basic regulator from Holley, been dead solid reliable now for over 20 years....

[dwelch]

thanks for the reply Cliff. ran that set up on my race only car for years. will start collecting the parts and be ready for the spring of 2019.  Denny

[Cliff Ruggles]

I would add that my system uses a bypass back to the tank to take the load off the pump.  It's a home made system right before the regulator.  I used a 3/8" NPT "T" into the bottom of the regulator and came off one side with a 90 degree 3/8" to 5/16" inverted flare fitting to the factory return back to the tank.  I made a provision to shut it off for racing but have never ran into any fuel delivery issues so leave it open.

When the system was first installed I ran it "dead-head" and it fried the pump in a couple of months of street driving.  At that time I  bought another one, and added the bypass.  The original pump was rebuilt and shelved (only needed brushes).  The pump acts much better with the bypass, quieter and obviously lasted much longer than running it "dead-head" as it's been in service now for almost 20 years......Cliff

[tayto]

I use the same basic regulator from Holley, been dead solid reliable now for over 20 years....

i meant using a regulator on a non-electric pump

[Cliff Ruggles]

I've used them with mechanical and electric pumps w/o issue....

[tayto]

Should I get a regulator with a return line or is it OK to let the mech pump handle the return? My truck has A/C so has factory return line I believe.

If i was able to lower my fuel pressure from 12 psi to 5.5 psi could I in turn then reduce my float height? With my setup you recommended 9/16" could it be lowered to 1/4" as discussed if your book?

[Cliff Ruggles]

For the Edelbrock 1904, 1905 and 1910 units and most later model factory Q-jets I typically set the fuel pressure around 6-7 psi and the float at 9/32"......Cliff

[tayto]

Thanks Cliff.