willysmjeeps.com

I have a 1953 M38A1 with a recently installed military fuel pump and new in-tank screen and pick-up tube. The Jeep runs fine for about 10 miles then it begins to "cut-out" and then comes back intermittently. It gets progressively worse until the Jeep will no longer run.
Is this an ignition problem or a fuel problem? I appreciate any advice folks may offer to diagnose and fix this.

Thank you.

Sounds like vacuum lock. Verify your fuel tank is vented properly... You can verify this by driving around with the fuel tank cover loose, or check and see if you fuel cap has the ability to be "Vented" or "Closed"... if so switch it to vented.

Hope this helps...

Just take the cap off all the way. Inspect it to determine if it is fixed non-vented or like the third photo. If like the 3rd photo select vented , re-install the cap and then test drive. If it is like the first two photos then leave it all the way off and drive it. If engine still quits checkout fuel feed for restriction. If itdoesn't quit then check the tank vent itself for restriction.


Older un-vented cap


Another early unvented cap.


Late two position cap incorporating a manually selectable valve for vented or un-vented.