Needing help and it has nothing to do with my age!

[Jim Boy]

Good day folks. I have a brain burner going on. The story.. 68 truck ran perfectly to the golf course. On the way home it started to backfire on acceleration. I though it was mad at my score but it continued all the way home. So I thought that with the crappy fuel we have nowadays it must be in the carb. I had a kit so I rebuilt it. Fired up the money pit and it ran perfectly until it got hot and then the same problem occurred. I talked to a few knowledgeable guys and they said carburetor. So another kit and dider again. Same thing, no worky right. So there was two choices. Either beat the heck out of this money pit or be nice and spend some money on way overdo items. So I chose the latter and did a lot. It got new points and condenser, new coil I had in a box on the shelf, plugs and timing done. I even replaced the carb that c/w automatic choke for my old one from another engine that c/w manual choke, that engine ran perfectly. Same result.
So the 250 engine is idling for quite awhile while I'm standing there reading about the different needle movements on a vacuum gauge, when the engine just chugged a couple times and quit. We stared at each other for a while as I was not going to let it win. I figured that it ran out of gas from the carb. I took the top of the Rochester Monojet off and when I lifted it up the gas gurgled into the fuel bowl. Now I'm a thinkin that I either have a stuck needle valve or my fuel pump is not doing the job after it has ran for a while. When cold, the engine will accelerate like it should but when it gets warm, bingo, bango, no ticky no worky.
That saying of "less is more" doesn't apply to old farts that like to talk(or type) as you probably have noticed. Just trying to eliminate questions. I will treat all replies with great interest and report as to whom is the winner.
Have a good day eh!

[Dead Parrot]

If the problem only happens when it is hot, could be a variation of vapor lock, where the fuel is boiling in the lines. Possible you got a batch of "winter gas" that vaporizes easier in cold weather but can cause issues in really hot weather. Your first thought of 'bad gas' might not have been so far off.

Also suspect a possible fuel tank vent blockage.

New distributor cap?

[Ziegelsteinfaust]

On my Q-jets which are prone to vapor lock. I triple stack the 1/4" gaskets they give you, and I haven't had vapor lock in a long time. My current engine uses a bypass regulator which i am sure helps quite a bit

[mattfranklin]

What those guys said, plus to test for vapor lock you could...
1) Drain your tank and fill it with fresh summer gas
2) Wrap your fuel line with aluminum foil, and better yet, leave room for ice cubes to be stuffed next to the line
or 3) Put in one of those see-through filters right before the carb. I would not recommend that long-term because of the risk of housing failure and fire.

These are all serious suggestions. Earlier in my working career I took several trips to Yakima, WA to join the CRC volatility testing programs. It just depends on what is easier for you.

[samert111]

Bad spark plug wire.

I had 64 SS Impala back in the 70's. Had a miss and backfire under acceleration once it got up to operating temp.
Recently installed new plug wires so I didn't even consider that was the issue.
After a complete tune up except plug wires I finally swallowed my pride and took it to a Ward's auto center and within a few minutes they diagnosed a bad spark plug wire and grabbed a used one out of the trash and sent me on my way.