I need help on this problem. It happened out of no where.I have a 71 which just
went thru a 3 year resto. The motor is a 4 cyl. 2.0 built up to 2.4 with weber 40idf carbs and about 1200 miles on the new motor. I was having what seems to be a
fuel problem. I would take the car out and after about 15 or 20 min. the motor would start stumbling like it was not getting fuel. It would get worse then start to stall. I removed the gas tank and it was spotless on the inside,I removed the screen and cleaned it, I made sure the line from the tank to the carbs is clear.
I installed a new Carter pump,I removed the Holley regulator and ran new -6 lines
to the carbs. When I fired it up with the new pump it was pumping about 5 or 6 psi and I noticed it would drop to about 3.5 psi after it would start stumbling.
Ther are no kinked lines.What am I missing here. I also removed the carbs and cleaned out all the jets. Could this be motor related?

tank vent? bad ground or power for the pump ?

although even 3,5 psi at the carbs -should- be enough to keep them fed...

i can't think of anything motor-related that would correlate with low fuel pressure right when you experience the problem ... i can only suggest finding out where your pressure is going...

what kind of filter are you using, where is it, and what kind of condition is it in? (i used a K&N micron screen filter on one car, has nice AN-6 fittings built right in ...)

i suppose it could also be vapor lock depending on where your pump is located and if any of the lines are too close to exhaust components... just a thought...

Hars, the last time you posted, we spoke of eleminating the vent aspect of your fuel tank. Has this been done? and if so, what happened.
L. McC

If you think you have a vent problem, remove the gas cap for a drive and see if the problem persists.

The other could be the suction line to the pump is collapsing.

I added another vent at the cap. I have a Russell micron filter located at the end of
the fuel line right before the tee fitting. As far as the line collapsing at the tank I will have to check it.My main line in the tunnel is a 5/16" hard line.
I can hear the pump running all the time even when it starts missing. I installed
a painless fuel pump relay kit so I know I am getting good power. As far as vapor lock, my lines are not near the exhaust and my pump is in the front trunk.I also wrapped the line where it exits the rear firewall with heatwrap.This is really a strange problem. Like I said it just started out of nowhere. I never had the problem in the first 1000 miles of driving.

Ok, I'll make the assumption that you are not blowing black smoke due to an overrich condition of the float valve sticking and pushing pressurized fuel thru the carbs..........,

1.) Do you have the bakelite insulators between the heads & manifolds? = Avoidance of boiling fuel in the carb bowls. Also some vibration elimination.

2.) The -6 line - Is is the Russel or Aeroquip (rubber) line - Russel deteriorated real quick on the race car and I would never use it again (even if they said they improved their quality)

3.) I'll assume that all the fastners on the manifolds/carbs are secure. Heading toward an intake leak as the metals expand.

4.) With the drop in fuel pressure - to me it would have to be a collapsed/plugged line or the float valves sticking open.

Hey, it's all a guess

Slits,
I have Russel lines that are brand new.No black smoke.
I will check all the other items you listed and let you know.