hey guys, so my car was running like absolute crap for a while, and I finally got her running nice, the problem it had was that after 2500-3000 rpm it wouldn't pick up rpm anymore, and it just sputtered and backfired, so anyways after setting the timming, a valve job, carb cleaning and new plugs rotor and cap, it still wasnt fixed, then i changed the condensor on the dizzy, well this fixed it and it ran absolutly awsome for about 15 minutes, then all of a sudden it started popping and sputtering again, but a different type of sputtering cause i could still rev past 4000 rpm, it almost sounds like it runs on three cylinders, but every once and a while it will run good for a few seconds, so what you guyus think the problem might be? i was thinking maybe a plug wire is causing this to happen.
any help would be fantastic.