mysterious backfire

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May 21, 2002 | 03:40 AM

puller1

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Joined: May 2002

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From: harrodsburg usa

mysterious backfire

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?

May 21, 2002 | 11:31 AM

rocky

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mysterious backfire

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.

May 21, 2002 | 12:03 PM

400m

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Joined: Sep 2001

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From: Lincoln, Rhode Island

mysterious backfire

I would also check for a broken valve spring or even a burnt valve but I think that is more likely not it, but it could be.

400m

May 23, 2002 | 07:45 AM

wayne_j

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From: cedar rapids usa

mysterious backfire

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.

May 23, 2002 | 08:01 AM

shazam

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From: Porterfield

mysterious backfire

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.

Just food for thought.