I have been stumped on this for a while, It's time to ask the pros.
I have a 71 chevelle with a 540 in it. When it is first started I have about 8lbs pressure as it warms up it starts dropping finally drops to about 3 lbs. I have installed 3 electric fuel pumps and 2 regulators all had the same problem.
I also tried bypassing the fuel tank and line (sucked fuel from a gas can) and still the same problem. Any help would be appreciated.

Thanks
Ron

Faulty guage???How does it run??

I had a POS liquid filled gauge that did the same thing you are describing. Replaced it with a name brand non liquid, needle bounces a little, but it stays right on the money. Liquid filled dropped as engine warmed up.

Under normal driving no problems, under heavy acceleration the bowls empty (about 2 blocks)and you need to back off the throttle so the pump can catch back up.

Tim it sure sounds like you have a fuel line problem,or filter or filters that are loaded up.If you are running the original fuel tank,it could be full of rust or other contaminates.You have pretty well covered all the other bases.

I am using a new tank (1970) and new 1/2 fuel line, the only part that was resused was the float & sensor in the tank.

If your running out of gas, and then having to stop to let the carburetor load up, your float may be out of adjustment or even cracked.

float is fine and is set 1/2 way up the sight glass (per Barry Grant)

I'm assuming you checked the fuel line for kinks or pinches along the route. Just a thought. You say you have a 1/2 line to the regulator. After the regulator, how are you delivering the fuel to the carburetor? Fuel log, two lines and a block from the regulator?

There is a slight kink at the sending unit (I don't think that's the problem b/c of bypassing the tank and lines to the regulator when I fed it from a gas can). Originally I had 1/2 to a #8 dual feed line, Now I have 3/8 from the regulator to the #8 feed line (I tried this hopping to increase the pressure.

I feel your choking fuel with the 3/8 line, then opening up the dam when it gets to the #8 dual feed.The 3/8 regulator line can't keep up with the demand of the dual feed lines.Check into going back to the 1/2, and replacing your feed lines to a #6. Call Barry Grant or Holley with your situation and ask them first. Good Luck

I will give B/G a call and see what what they say.
Thanks for the help
Ron

Ron, did you ever get this figured out???

Are you now running an electric pump? If so, have you double checked wiring? Is is it the proper gauge for the length of run? Does this problem occur only when driving to 'warm up' or can it happen while idleing for the same period of time. Could be a heat issue with the pump if it doesn't matter if you are moving or not. Just a guess...

Would also think about checking the wireing..Do the wires get hot going to the fuel pump which might indicate an issue with the wires. Does the pressure drop from 8 to 3 at an idle or just when you get on it?
Steve B

Ron,did you ever get this problem ironed out?

check hard line for slight crack or were pick up is at tank,possible hose cracked sucking air.

Hi all,

I have what seems to be the same problem as 71 Droptop. I set my pressure at 7lbs and it will slowly go down almost to nothing. I notice this happens when driving and sitting still. I just came from the garage after I sat and watched the pressure drop. It took around 20 minutes to drop to almost nothing. I notice the problem when under high acceleration and burnouts that my power would cut out.

I never had this problem before I installed a new electric Edlebrock pump. Thinking I got a bad pump I got another Edlebrock pump that resulted in the same problem. I also got a new regulator too that didn't help.

My line is 3/8 all the way through. The lines are clean and I double checked the flow. There's certainly plenty flow.

My next move is to put the old (Holley blue pump) pump back in and see how things go.

71 Droptop, please keep me posted on your progress. Also, how do yo have your pump wired and a what the location of the pump?

C-munkey

I believe that the problem lies with the size of your lines. If you wired your pump according to directions, that shouldn't be your problem. In order to keep pressure in your fuel lines or any other application for that matter, the basic rule is every time you branch off the line, you should step down one size after the fitting. I know I'm comparing apples and oranges here, but the same theory applies.
Check your water lines coming into your home. The lines from the street(or pump) and into the house are approximately 1". By the time you get to the last faucet it's down to 1/2" lines. If they were all the same size and you were washing your Chevelle off the last spiket and someone up the line opens the line, they wouldn't have any pressure. It would all flow towards you. Especially if the faucet is higher than your feed line.
If you have the same size fuel lines all around, the pump will flow ok, but with no pressure. The fuel will take the path of least resistance, like through the regulator and back to the tank. Not up the carbuertor lines. There's nothing there to slow the flow down and build pressure.
Good Luck

Hi all.

I got my pressure problem fixed. What I did to fix it was to install a return line back to the tank. I talked to some pump manufactures and they say sometimes pumps with internal bypasses have tendency to bubble up inside. Getting just enough extra fuel moving like using a return line seems to work for me. I have had dead headed fuels systems in other cars before with no problems but for some reason in this car it is a problem using a dead head system. I'm not 100% sure why a dead head system is a problem on the car but the car runs great now.

Thanks for all the info provided on this thread.

I'm gonna go Cruzin Now!!!