I just rebuilt the lower end in my 79 150 with 302. For about 5 months it ran fine. I rebuilt carb. New cap, rotor, plugs, coil, I didn't touch the distributor though. All vaccum lines are hooked up fine and are in ok condition. Then one day without warning i went to start it and it wouldn't idle. I took it down the road it ran fine but would die when I would stop. Then all of a sudden it will cut out and buck to beat heck when i get up around 50. You can play it acclerator but it will not come out of it. You have to let it die. It will then start fine and go down road fine from any where to 30 seconds to 2 hours. It come and goes. Seems like if it does that, it works to let it die, start it, then let it sit and idle for about 5 minutes it won't do it. I don't know what it is. It is not a constant problem. Comes and goes. I can run around town at slow speed with no problem but when i'm out on highway I can drive 5 miles before it starts or 100 miles with no problem. i'm almost scared to go about 50. It starts fine, acceltates fine. Any ideas? I assume it is carb problem or could it be timing?

Flyhound

 

Might want to look for a clogged pickup screen in the fuel tank.
Same conditions you describe, chased it for a while before pulling the tank and finding the screen clogged with rust.
Real headscratcher because the problem was so intermitent.

 

old_rusty, that's a good idea.

I have also seen the ignition box act up and cause strange problems like this. I would swap yours out and see. If it does not fix your problem hang onto the box anyway. It's a good idea to have a replacement box in the truck. It took me 2 times of being stranded due to a failed ignition box before I learned to keep a spare one in the truck.

Good luck,
Lee