Why is my car ( all of a sudden ) backfiring when I shut it off ? It really doesn't bother me but I almost gave some old doll a heart attack. I just replaced the pump diaphragm in my Dellorto 48mm...small leak...but that is about all that is new to it.

 

Cats gone?emissions removed?My 12a did it all the time without emissions and cats.

 

You have that right sir, but it's been that way for about 2 years now. I can't figure why all of a sudden now ???Could I be running it too rich ?

 

Have you checked your timing?



Mine used to do it when the timing went out a bit....

 

Yah Id say timing as well.

 

Yea,I guess I'd better, I've never messed with that ,but I'm sure it can't be that hard to adjust... I've got the manuals...Thanks all

 

The guy who I autocross against used to have that problem with his old motor. Every time he'd shut it down it'd backfire. He was running a heavily streetported 12A with dual Weber 36DCDs. He built a 13B and switched to a 52 IDA Webers and doesn't have the problem any more. I bought his DCDs and bolted them straight on and haven't had hardly any backfiring at all, running or shutting down. AFAIK we're both running 24*/16* timing. What exhaust are your running? Any leaks?

 

If your timing is too far retarded, then it will cause excessive exhaust heat. Then when you shut it down, the heat ignites the remaining fuel and you get a backfire.



I have no emissions, and Racing Beat exhaust. I used to get shutdown popping until I adjusted my timing.



Also, make sure that you have no leaks in your exhaust system.

 

You should check your ACV and cat to make sure they are working properly.

 

My '79 started to backfire on shutdown and sputter when engine braking at high rpm. The ACV was shot, so I simply pulled it (no emissions testing here...yet) and used a blockoff plate I'd had kicking around for ages. That caused the motor to idle really poorly, so I upgraded to DLIDFIS which solved that issue nicely!