1973 F250 - 390CI - runs poorly
I never thought I'd appologize for having a long post, but.......
I got this old Camper Special. It has a new 3" dual exhaust, and a Carter AFB (750CFM) instead of the original Holley. It ran so so.
I put in a new set of points, cap, rotor and plugs. Timing was OK. It seemed to run a little smoother than before.
Still it stumbled at low RPMS, it would really bog down coming off a stop unless I gave it quite a bit of gas. I have to rev it pretty hard before shifting or it stumbles again in the next gear.
Thus begins my quest for better performance. I had suspected all along the carburator was an issue. I don't think it's jetted right. So I took it to a mechanic. After discussing my symptoms and the problems I had resetting the timing, he suggested a I might need a new distributor. I purchased a remanufactured one from Vapex. Certain I had installed it correctly, I rolled it over, got a loud bang!, then started second guessing myself had I put it in correctly. I called the mechanic over, he verified that indeed it looked like the points were set right, the firing order was OK, and the distributor wasn't a tooth off. We tried it again. Same thing. Crank, bang! then nothing.
After doing a compression test, the mechanic determined it may have jumped time. From everything I read, it seemed plausible. He hauled it in and replaced the timing chain and gears. Afterwards, he claimed it ran very rough with the new distributor. So he took it off and put the old one back on. It ran better than it had before for the first few hundred miles. But now I'm experiencing the same issues I had before I started, even worse. It starts hard (I replaced the battery after all that cranking) it backfires when I try to start it, it backfires sometimes coming off of idle. It still stumbles like heck and I've lost confidence in my mechanic.
So...should I go after the ignition? (plug wires, update the distributor to electronic etc.) Or try to rejet the carb or go back to the Holley. Or something else (ring job, valve job etc.) Could I be overlooking something?
Thanks in advance for the advice. I look forward to hearing from other big block owners with similar issues and proven answers.