Changed nothing on my car and it went from running good to a miss under load part throttle. If I stab it it smooths out. Idles revs and cruises fine but when accelerating it breaks up. Check a few plugs and the are right on, timing is good, wires are new floats are good ?? Fuel pump (electric) is a year old as is filter, fresh 93 octane yesterday...
Maybe a problem in your exhaust system. I had a 69 Chevelle where the pipes where 2 layers and the inside layer collapsed caused the same condition. Just a thought, good luck
Check the mechanical advance weights in your distributor to be sure they move freely and aren't sticking or binding. I had this problem a couple of times and it was always the plugs. A fresh set would be cheap. One of the insulators could be cracked. Double check your wires again, in the dark while running, and mist a little water on them and the dist cap before you start.
Definately distributor ,Had the same problem on my Pontiac......Pull distributor and find replacement....
the breakerplate in your distributor could be bad i had the one in my 351 cleveland go bad acted just as you describe
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