DougRussell

Hi All. Have a 86 Camaro Z28 with 383, Alumin heads, Holley 750 Vacuum, air gap intake etc... I wont get into too much engine details but here is my problem. Was running a 7.8 in the 1/8 mile at the track with my setup first weekend out. Changed to high volume fuel pump but it did not have a return port so plugged the line. Still has factory tank and lines with breather up to engine. Car is getting slower by the pass and in fact has slowed to a 9.0 over the last weekend (8.0, 8.4, 8.8 and 9.0). I think I have a fuel problem as the car seems to run out of steam the higher the RPM I go. Is it possible that with the plugged return I am creating a vacuum in the tank restricting fuel to engine?? I am thinking of putting a factory pump back on with return but want to ask for opinions first. No changes to engine and timing, valves and all have been verified over and over again. I am at a loss here. Maybe the fuel pickup sock is plugged or the vent valve is plugged?? Just some guesses.

RedLeader289

iTrader: (2)

I've had that same set up for over a decade now with no issues. Granted, I'm not racing but still.

Is your fuel pressure steady? fuel filter clean?

DougRussell

Fuel pressure 6-7 psi at the carb and seems steady from what I can tell. Clean fuel, new clean filter before the carb as this one does not have one underneath.

RedLeader289

iTrader: (2)

I wouldn't think it's a fuel issue then. There's a host of other variables though.

NoEmissions84TA

iTrader: (1)

Try making a pass with the gas cap loose or removed.

Remember, the metal fuel lines are tubing, and tubing is measured by the OD. Therefore the ID is smaller.
Now I can't speak for everyone else here, but my 84 Trans Am would run out of fuel in the carb bowls (E4ME) just as I shifted into Drive (700R4) during a 1/4 mile run on the highway (108 mph).
Stock metal lines, tried 3 different mechanical fuel pumps, nothing made the situation any better. I checked every inch of the lines for kinks - none.
I made my own tester like you use for NOS, where you screw a Holley jet in the end and then see how much time it takes to pump 1 gallon.
So I ran flow tests to determine where the restrictions were any by how much. Long story short, the total of all the small restrictions added together came up to 19 gal per hour. This was from pickup sock in the tank all the way to the carb itself. The largest restriction was the long 3/8" line itself.
I band-aided the problem by adding one of those small electric fuel pumps near the tank to give the fuel a push up to the block mounted mechanical.