[jks67SS396]

ok guys,

I have a 540 SR AFR headed BBC with 2" hooker comps. 1/2" hard fuel line coming out of a stock tank and pickup (67 camaro, real 396 car... 3/8" pickup??)

when i fire it up, the gauge on the carb says 7 psi. after i take it for a short drive, its 3 psi.

the friggen fuel line runs right by the headers and i can imagine the heat.

im also not so sure about that carter 172 mech pump. it seemed like it was acting up on my last motor.

fuel atomizing from the header heat???

carter 172 puking out?

should i try insulating the hard line near the headers with some kind of wrap or something?

thanks guys

 

[aukai]

I ran my 1/2" hard line through the frame like stock and have a 172 fp no problems maybe re route your fuel line

 

[Sandy]

The only reason for running higher fuel pressure is with small fuel line.

If you have a large line (large area) you don't need so much pressure to supply the needed volume to keep your fuel bowls full.

 

[Dave]

I'd get that fuel line away from the header's, can't be helping nothing.

 

[Gokou]

Is it a glycerin filled gauge?

If so, as the gauge heats up the glycerin expands and exerts additional pressure against the bourdon tube inside the gauge housing causing it to read lower than actual pressure.

This is a very common problem I see on all underhood glycerin filled gauges. As the engine compartment heats up the pressure readings go down, it's very obvious on a low pressure gauge such as carb'd fuel systems. Guys set their pressure when they first fire the motor while everything is cool, take it for a spin, and when they get back the gauge now reads several PSI lower than when the gauge was cold, so they crank the fuel pressure back up to 6-7 psi with the hot gauge and start pushing past the needle & seat.

I was just finishing off a nitrous install on a car tonight actually; when the engine compartment was cold I set the fuel pressure to 7 psi with the gauge mounted on the rail and confirmed it with my very accurate 3" external test gauge. Took the car for a spin and when it got back the gauge on the fuel rail now read 3.5 psi. I hooked up my good external gauge and the pressure was still at 7psi where I set it.

 

[jks67SS396]

thanks guys!

very very informative! it is a liquid filled gauge, so that may very well be what is causing the problem. maybe this weekend, ill try to reroute the hardline somehow too. or wrap it?

thanks guys

 

[72moneypit]

Mine does the same thing. I set the pressure cold and forget about it. From time to time I check it cold to make sure the regulator is staying put.

 

[Mike McMasters]

What Gokou said is true. Easy solution is to burp the air out of the guage right before you take your reading. There is a small circular rubber plug on the rear of the guage. Take an awl or small screwdriver and push the plug to the side for a second. This will release the pressure trapped inside and give you a more accurate reading.

Mike

 

[72moneypit]

The air bleed is good info, I will give that a try.