Why Is My Car Backfiring Out Of The Exhaust?

[PJ]

I've noticed an issue with the 73 Corvette lately.  When accelerating and the RPMs get just about to 3000+ the engine will pop out of the exhaust, also known as after fire. (I put backfire in the title because regardless of being right it seems more people use the term backfire, which is out the intake/carb)

Several things could cause this and I did a little research before diving in because its the smart thing to do, learn from others.  My fix turned out to be really simple but I also want to touch base on another potential problem or 2.

For me it was simply a timing issue.  I retarded the timing just a bit and the popping went away.  

Another possible cause seems to be basically any component of your ignition system.  I read another forum where it was suggested the guy change the spark plugs and wires.  That didn't work but then he replaced the coil and that fixed it for him. 

Lastly a common suggestion I saw was that their was a problem with the amount of fuel the engine was getting when the back barrels were opening up.  To test this theory you can disconnect the back barrels so that the carb functions like a 2 barrel and see if you still have the afterfire.  If you still have it then thats not your problem but if its gone then you have at least isolated what is causing your afterfire.

This is what I learned this weekend. Maybe some time down the line this will help someone with a similar problem.

[Yukon]

Didn’t you say in your vid that you found a plug wire contacting the exhaust? Are you positive the timing was the issue? A shorted plug wire can damage a coil. Just a thought in case you start having other issues. Gotta keep the vette up and running for the next giveaway.
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Btw, I do NOT miss setting timing and potentially shocking the shit out of myself like back when I was 16/17.

[PJ]

Didn’t you say in your vid that you found a plug wire contacting the exhaust?  Are you positive the timing was the issue?  A shorted plug wire can damage a coil. Just a thought in case you start having other issues. Gotta keep the vette up and running for the next giveaway.
>

Btw, I do NOT miss setting timing and potentially shocking the shit out of myself like back when I was 16/17.

Its possible but I don't think so.  They are pretty much brand new MSD wires so they don't have any cracks or wear to them... other than the spot that touched the header.  I taped it for now and re routed the wires with some wire separators to keep them away.  I'll have to see if its possible to buy 1 wire.  I hate to replace the entire set because of that one.  Anyway it was still popping after I did all that.  I was planning on replacing the coil because I felt like that was most reasonable but since adjusting the timing was free I did that first.  Drove for about an hour and it hasn't done it since.  Fingers crossed all is well.

The worst I ever got bit was reaching up under the dash while the Caprice was running and accidentally grabbing the wire going to the tach.  I don't remember what I was doing but I remember it lit me up pretty good.