[C2] Backfiring Problems
Thread Starter
Intermediate
Joined: Jul 2016
Posts: 31
Likes: 1
Backfiring Problems
My 1964 (327/300) has a sporadic backfire problem. Recently had it tuned up, new plugs & wires and distributor, compression is excellent, but it backfires quite often. # one cylinder is fouling the plug. My mechanic is a bit confused, since not many obvious issues. Any ideas? Do I need a new mechanic? Thanks!
Team Owner
Joined: Mar 2003
Posts: 31,248
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From: Wilmington N C
St. Jude Donor '14 thru '26
My 1964 (327/300) has a sporadic backfire problem. Recently had it tuned up, new plugs & wires and distributor, compression is excellent, but it backfires quite often. # one cylinder is fouling the plug. My mechanic is a bit confused, since not many obvious issues. Any ideas? Do I need a new mechanic? Thanks!
Safety Car
Joined: May 2003
Posts: 4,797
Likes: 239
From: Ocean Township NJ
My 1964 (327/300) has a sporadic backfire problem. Recently had it tuned up, new plugs & wires and distributor, compression is excellent, but it backfires quite often. # one cylinder is fouling the plug. My mechanic is a bit confused, since not many obvious issues. Any ideas? Do I need a new mechanic? Thanks!
If it's backfiring (pop thru the carb) then it could be a lot of things.
If it's afterfiring (thru the exhaust pipe[s]) then it's most likely an exhaust leak coupled with a rich mixture.
Team Owner
Joined: Aug 2007
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Army
Was this happening before the tune up? New DISTRIBUTOR???? Why, and what kind did you have before and what do you have now?
If it's backfiring (pop thru the carb) then it could be a lot of things.
If it's afterfiring (thru the exhaust pipe[s]) then it's most likely an exhaust leak coupled with a rich mixture.
If it's backfiring (pop thru the carb) then it could be a lot of things.
If it's afterfiring (thru the exhaust pipe[s]) then it's most likely an exhaust leak coupled with a rich mixture.
Last edited by Frankie the Fink; Oct 27, 2016 at 06:06 PM.
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Thread Starter
Intermediate
Joined: Jul 2016
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The backfire is through the exhaust. I only had the distributor cap replaced, it came with a tune up kit I bought. New wires came with the kit also, so #1 wire could be bad....will replace that one. Just recently bought this car and didn't drive it much before the tune-up, but it didn't backfire before the tune-up. I plan to replace the exhaust system soon, it is pretty old. Great ideas folks, thanks. Black64
Melting Slicks
Joined: Nov 2006
Posts: 2,618
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From: Anaheim California
Remove one plug wire at a time while the engine is running and see if there is a difference when each cylinder is isolated. If the engine RPM doesn't change when you remove a wire, that cylinder is your problem.
Last edited by jtranger; Oct 27, 2016 at 10:40 PM. Reason: add
Melting Slicks
Joined: Jun 2012
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From: Wilton Ca.
Usually, but not always, a (backfire) afterfire occurs due to an electrical misfire. You probably have at least one cylinder that is getting unburnt fuel due to lack of spark at some point then, the cylinder gets spark and......... boom, the excess fuel ignites!
If it didn't afterfire before you had the tune up then, it's up to the mechanic to diagnose the problem and yes, if he's unable to then, you really should find someone else since this should be an easy fix for any competent mechanic.
Gary
If it didn't afterfire before you had the tune up then, it's up to the mechanic to diagnose the problem and yes, if he's unable to then, you really should find someone else since this should be an easy fix for any competent mechanic.
Gary
Team Owner
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Army
The backfire is through the exhaust. I only had the distributor cap replaced, it came with a tune up kit I bought. New wires came with the kit also, so #1 wire could be bad....will replace that one. Just recently bought this car and didn't drive it much before the tune-up, but it didn't backfire before the tune-up. I plan to replace the exhaust system soon, it is pretty old. Great ideas folks, thanks. Black64
Popping in the exhaust (afterfire) is unburnt fuel lighting off in the hot exhaust. It is often caused by a lean mixture or timing misadjustment. You can try snugging down all the exhaust manifold bolts first. I always keep a spare of the longest plug wire and a good plug. If the problem is worth it to you then you can always replace each wire/plug temporarily through all 8 cylinders until you find the culprit. If you know which bank is the problem (left or right) then only 4 cylinders. That's assuming its spark...it could also be too high an idle or other carb adjustment.
The cylinder RPM drop test (pulling a plug wire on each cylinder individually with the engine running) most likely won't find an intermittent misfire.
Last edited by Frankie the Fink; Oct 28, 2016 at 05:24 AM.
Le Mans Master
Joined: Nov 2015
Posts: 7,508
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From: Really Central IL Illinois
I can't tell you how many bad "new" plugs I have had over the years. I go with Frankie on the plug replacement one at a time. If you have the old plugs, look for a good one with good color and gap and use it for the test.
The weak exhaust valve spring is also possible, but generally will give a consistent miss. I have had one break, but it wasn't obvious until I did a very close inspection.
The weak exhaust valve spring is also possible, but generally will give a consistent miss. I have had one break, but it wasn't obvious until I did a very close inspection.
Race Director
Joined: Apr 2015
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From: Fresno California
What Frank said. I've tuned a lot of cars, and having a car backfire (afterfire) out the exhaust due to only having an open plug wire doesn't happen. You need added oxygen to ignite the added rich mixture in the exhaust, as in an exhaust system leak. A very common cause for popping out of one bank is a burnt exhaust valve....that's what I find 7 times out of ten. Lean mixtures, open wires, bad dist caps usually cause a fireball-belching backfire out of the carb.
Melting Slicks
Joined: Apr 2005
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Originally Posted by GTOguy
What Frank said. I've tuned a lot of cars, and having a car backfire (afterfire) out the exhaust due to only having an open plug wire doesn't happen. You need added oxygen to ignite the added rich mixture in the exhaust, as in an exhaust system leak. A very common cause for popping out of one bank is a burnt exhaust valve....that's what I find 7 times out of ten. Lean mixtures, open wires, bad dist caps usually cause a fireball-belching backfire out of the carb.
