Very frustrating fuel or motor problem Options

[hars914]

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?

[ArtechnikA]

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...