Engine hesitation/ stalling

[phrog167]

My 72 F-100 has been acting up lately. It runs fine until I stop somewhere and then go to leave again. It then acts like it's not getting enough fuel and runs smooth only at idle. If I floor it, the engine acts like the timing is off, sputtering, backfiring etc.

I replaced the distributor cap the first time I had trouble when I saw that it was broken at the set screw in front allowing the cap to be turned a couple degrees. I also checked the points which were fine. Yesterday I noticed gas leaking from the accelerator pump on the front of the carberator. I found the diaphragm to be shot and replaced it. I just knew that would solve the problem. The truck ran great for a few laps through the neighborhood and downt the road a bit.
Same problem's today when I took if to run an errand.

One of the last times I had trouble I noticed a howling/ whistling sound and discovered that it was coming from the gas tank. After removing the cap there was a rush of air sucking into the tank.

The only common denominator is that the last three times I've driven it have been for about the same amount of time before the trouble starts. About 10-15 minutes.

I live in Rhode Island and it's been cold as hell when I had the problem the first two times. I thought ice from condensation could have formed in the tank or lines causing starvation problems. I keep it parked in the winter and start it every few days or so. It was in the high 40's today when I had the same problems.

Any ideas would be appreciated.


ED

[FORDification]

Your problem is that your fuel tank that is supposed to be vented....isn't. Your '72 should have a charcoal canister mounted on the front frame rail that's hooked up to the fuel tank and absorbs gas fumes, and includes a hose which stretches up to the air filter housing, to burn those fumes. This charcoal canister also acts as a tank vent. That whoosh of air when you removed the gas cap means that air isn't entering the tank as fuel is used up....and after a short while, the tank starts building a vacuum, and won't allow fuel to leave. It also means you have the correct non-vented gas cap, since a vented cap would allow air to enter the tank as fuel is used....but adding a vented cap now is like putting a BandAid on a broken arm....it's not fixing the real problem.

Either your tank's charcoal canister lines are clogged or they're capped off. Unclog or uncap the lines, and I'll bet your problem will disappear.

[phrog167]

Thanks Keith,

I'll check that next. I was going to check the fuel pump flow and pressure next. But, if I'm getting that much vacuum, the pump is probably fine.


Thanks again,

ED

[DuckRyder]

Also, a vented cap will not fit the 72 fill neck.

[CactusKid]

Wow, my 72 does the exact same thing. The mechanic at the Ford dealership has been losing his mind saying "It's hard to work on a car without computer chips". I remember the days when they accepted a challenge. I'm glad I found this site.

[1971fordcustom]

Mines done that for the past 2 years LOL im so use to it now Idk what I woud do if I fixed it.

[CactusKid]

Turn out the last owner got creative and removed a bunch of stuff from the carb and it was slamming shut...doh.

Thanks for all the info people