Stumbling after 20 miles of driving

[mr48chev]

There is no possible way that you can have a pressure build up in that tank except when it is sitting in the sun and heat. You have one line out and no lines in.

If it still stumbles when you leave the cap off the sock on the pickup tube is probably full of dirt or trash.
And I don't care if it is a brand new out of the box vented cap, unless you have tested it it is still suspect. As I stated earlier, I went through three brand name caps that were even marked vented but none of them would vent. I finally got a winner with the fourth one off the same parts shelf with the same parts number.

One other thing it could be is that the inside of the hose between the line and the tank is collapsed inside and sucks in and blocks off the fuel.

[Test Pilot]

I'm done posting in this thread. If any of the people that were following along want to know what I find tomorrow feel free to send me a PM. I'm not going to continue participating in a pointless argument.

[eagleuh1]

I had problems with dried hardened fuel flaking off the hard fuel line and plugging my sintered bronze fuel filter in the QJ carb. It looked like rolled up brown rice paper. I guess you'd call it shellac. This caused it to stall, sputter at higher speeds, but if I pulled over or slowed down and idled a little, it would clear up until I sped up again. Happened three orfour times. Just had to clean the bronze filter. Take your plastic filter off and check the inlet side for blockage. Mine happened after sitting 13 years with old gas in it. Good luck.

[splehigh]

Could be your spark plug wires. I had a similar problem that would get worse as the motor got warm. One of my plug wires was arcing against the block.

[westofb]

Originally Posted by Test Pilot

If I had a non vented cap I would agree with you, but the cap is vented. I won't go to the trouble of putting my manometer on it to prove there is pressure.
AGAIN the same problem happens when the cap is on or off the truck!!!!
When there is a 1.5" hole in the top of the gas tank, how can it be pulling a vacuum?!?!?!?!?!

he is right, from the pump to the tank, the pump will pull a vacuum on the tank, this is how it sucks fuel from the tank to be used in the carb....when i was talking about long lengths of rubber line, i actually meant between the pump and the tank. This is where the line will suck shut and stall the engine...from the pump to the carb the pump is producing pressure, rubber lines not that big of an issue on the pressure side, except for possible leaks and fire hazards! I would limit lengths of rubber lines in the fuel system to 2-3 inches, just to make connections between lengths of hard line or filters.