1980 US. Car is running and idling now. When I rev it up and then come off of gas completely, I get some back firing. Almost like a grumbling pop pop pop... not real hard backfire, but there and annoying none the less.

I am under the assumption that it is related to the fact that I do not have stock exhaust. I have manifolds that lead to pipes, and then just one single muffler toward the back.

is the back fire related to a back pressure issue?

 

No cats?

 

From your description, its probably running rich.

 

rich and or timing. my timing was off and caused that (with no cats). now with timing good, no bang bang

 

Jeez, have you never been a teenager?

That's part of the fun hot rodding around with glass packs!

BWAAAAAAAAAAAAAAA

BA BA POP BA POP POP BA

 

Reving it in neutral has little to do with anything....but you may also have an exhaust leak as well as rich running but until you DRIVE the car with fresh fuel hard to say what it is....put a couple hundred miles on it.

 

Funny..i have that tuned INTO my car.

"Fuel cut off at idle...disable."

Makes a beautiful popping ...gurgling ...Phhhhwooopping sound

AO is the only person that I kmow that has captured an image of flames coming out the tail pipe

 

no cats. I plan to take it for a drive tomorrow after the master cylinder goes in with 4 lines bled as well. Then I will just give it a nice smooth and easy run. I posted another thread with this car idling on video. here is the link to the vid. you cant hear the backfire due to obvious reasons... I am outside of the car and behind it.
http://www.youtube.com/watch?v=-fxAM...ature=youtu.be

 

the audio sounds horrible on my laptop. It sounded much better on my office computer with a subwoofer.

 

Probably a bad decel valve assembly.

 

This actually.


Leedee - take a look at the large vacuum valve to the passenger side of the throttle body. It will connect to the throttle body with two short hoses (roughly 1.5" long). The valve is supposed to open to lean out the mixture when you let off the gas - and then close up again when the idle has come down.

I don't know if there is a way to test the, but in my case when I pulled mine off I could hear the diaphragm shaking inside. Here's a discussion (pros and cons) of this https://rennlist.com/forums/928-foru...ve-delete.html

 

We're happy to help - think nothing of it...

 

I would also check that the idle switch is adjust correctly. Both my WOT and idle switch were not working as adjusted when I got the car.

 

We are talking vacuum limiter when saying "deaccel valve"?

I don't think it changes the mixture, it just bypasses the throttle so manifold vacuum doesn't get so high the normal mixture doesn't fire.

Putting some miles on it before getting too concerned sounds like a good idea.

 

I believe he is just winging it up in the driveway in neutral as it is not drivable yet !! Got it to start with some jumpers on relays, doubt that ignition timing and cam timing has been looked at....driving it a couple hundred miles with injector cleaner might do wonders for it !