I have a L69 car with a Edelbrock Carter AFB carb. The carb is tuned correctly.

While I was tuning the carb, even when I had the car too LEAN, my car afterfires really badly after hard acceleration. For example if I go WOT everything is fine until I lift the throttle, then I get "pop, pop, pop, BANG". I had someone follow me at night and they confirmed a big fireball out the back.

This is quite ghetto. I need to fix it.

I have headers and I want to put a highflow catback on but I don't want to do that until I get this fixed as it will amplify the already quite obnoxious explosion noise.

What else could be wrong? Timing?

 

What is the rest of the motor?

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"So many Mustangs, so little time..."
ICON Motorsports

 

Performer RPM manifold, Edelbrock 1405, not sure of the cam, think it's stock L69 cam, Edelbrock headers, A4 trans, stock L69 heads.

 

Afterfire kicks ***

 

What kind of muffler are you using?

 

OEM. (GM)

 

To a point. Big fireballs and explosions are NOT. My GF wants to know what the **** is wrong with my car! LOL

 

Well, you've got a manifold with a relatively giant plenum, that takes a while for that little engine with no flow to empty out. Think about it: you floor it for a while, the carb dumps all this fuel in there, you snap the throttle shut, now what? the fuel is already in the intake, so it has to go somewhere. But, there is far too little air coming in to burn that remaining fuel, because now the throttles are closed. The excess fuel will pass unburned through the motor and out into the exhaust, and boom! especially if you have any exhaust leaks or if the AIR is still working, either of which will supply some oxygen to complete the process of burning the fuel.

Watch a NASCAR race at night like Richmond or Bristol sometime, you'll see that all those cars do the same thing. It's inevitable. The only way to get rid of it is to dump less fuel into the motor at WOT, which might or might not be acceptable. Basically if you tune a carb for max power, that's what's going to happen. Really, none of the other components matter at all.


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"So many Mustangs, so little time..."
ICON Motorsports

 

fooey. Thanks for the good explanation though. Makes sense, if I roll out of the throttle it doesn't do it.

I do have an exhaust leak so I guess I'll go ahead and put on a Hooker catback. I'll check out the AIR system and see what I find.

muchas thanks!

 

Theres two valves in your AIR system. One is the divert valve which switches from pumping air into the manifolds when cold, and then switching to the cat. The other valve vents all air output to atmosphere on rapid decel to prevent afterburn. I would suspect this first.



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'88 Camaro RS 2.8L
'88 Formula 350 (Too many mods to list...)