85 gs. looks like the previous owner deleted all the emissions controls, and has aftermarket exhaust (cheap glass pack with no more glass in it)

so when im decelerating, mainly from high rpm's i get a pretty bad backfire, at lower rpm's too but not nearly as loud. i know to some extent a small backfire on deceleration with aftermarket exhaust is somewhat normal but this is like a shotgun going off. i think ive heard somewhere that a lean or rich (cant remember which) can cause it. is that right? anything else to look for?
im going back to stock exhaust so im hoping that will help some too

 

I have an 80, stock exhaust and it does the same exact thing

 

Anyone know what to look for? I know there's supposed to be an anti afterburn valve. But i don't know where to look to see if it's still there or how to test it if possible. Other than that though I'm lost as to what to look for

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On a stock system the most common causes of afterburn are a failing ACV, or a bad/missing dashpot that's letting the throttle slam closed too quickly.

Your AAV probably got chucked when the emissions were deleted; On SA's they are part of the ACV assembly. I think on FB's they are separate?

Can also be related to a sticky advance mechanism in the dizzy, I believe.

 

Chances are you have a leak in the exhaust system. Fresh air gets drawn into the piping, and then BANG! Fix the leaks and you'll fix the backfiring.



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I have an 83 that a previous owner had also done an emissions delete from, along with all of the old exhaust being replaced with one lone piece of flex piping. It would idle terribly for the first 15 minutes of running and backfire like mad. First I went to a local muffler shop and had them put on a whole new exhaust. there is a place near me that did it for 150 not including the muffler, I know it's cheap but better than nothing. Secondly, run a fine tooth comb through the engine bay and see if there are any loose vacuum tubes that are sucking up air. I plugged a tiny 2mm tube and my car instantly ran better.

 

if it were the dashpot wouldnt it try to die in neutral when i let suddenly let off the throttle? cuz it doesnt do that. but what is the ACV?
as far as the AAV i think it is seperate. i believe i read somewhere that it was on the carb? can someone confirm that?

i really hope thats all it is! i do have a nice exhaust leak. i think from the cat. gonna replace that with a resonator pipe (once i get a new muffler)

 

on the 85 the aav and the acv are seperate. Also, I was under the impression that a smog delete means a cat delete too, unless you like burning up cats.

 

I would think so too, apparently the previous owner didn't though, for that fact he didn't think it necessary to tighten the bolts on the tie rod ends, or do anything right for that matter...

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