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351m backfires at an idle. once revved up it stilldoes it just farther in between. i have adjusted my carb and timing so many times i could do it in my sleep. good plugs and wires. also when cold it will miss on 2 cyls. but once revved up it smoothes out .any suggestions?
When it's two cylinders acting up, I'd think the timing gear is going out, and it's bent the push rods of two cylinders. Or, a lifter could have gone south. At least that's what I experienced.
See the post about 351m back firing in this thread. Follow the directions there for hooking up and reading a vacuum gage. Generally about 80% of all engine condition questions can be answered by how a vacuum gage reads/acts. A backfire like yours, and also described in the other thread, kind of sounds like an exhaust valve that is sticking or a valve seat that is cracked.
Hey could it be possiable you got a couple plug wires mixed up.
A long time ago I had a 1967 Camaro and the #5 & #7 cly. fire after each other . if you mixed them up you'd get a miss and a back fire out the exhaust.