Popping through exhaust during deceleration

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dartsport74

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I'm trying to get a straight answer from someone with experience, this is my first build with this much horsepower. The car pulls great, but when I let off the throttle The car pops pretty loud and even will shoot a little fire out of the muffler. I don't like the popping and can't imagine it's great for this to happen all the time. How is best way to rectify this. My spark plus look like I'm running pretty rich, but I've read that the after firing is actually a sign of a well tuned engine but others say it's too rich and still others say it's lean, any experience/advice is much appreciated.

The engine is a 400 stroked to a 512, about 12.5 to 1 compression, 680 lift comp cam, Indy top end fully ported and a Dominator 1150 reworked by Pro systems.
Thanks again
 
An exhaust leak could cause the popping, but the unburned fuel is probably the main culprit here and that could very well be from late timing and/or way rich both.
It's hard to believe it's too lean if the plugs show rich.
 
When this happened with my brand new build, it was too rich. Do you have an air/fuel ratio meter? Are you hitting the brakes hard or just gradual slowdown? Sometimes hard braking can slosh fuel into the carb from the back bowl air vent.
 
TrailBeast said:
An exhaust leak could cause the popping, but the unburned fuel is probably the main culprit here and that could very well be from late timing and/or way rich both.
It's hard to believe it's too lean if the plugs show rich.
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I'll check timing next, Thank you your help
 
RockinRobin said:
When this happened with my brand new build, it was too rich. Do you have an air/fuel ratio meter? Are you hitting the brakes hard or just gradual slowdown? Sometimes hard braking can slosh fuel into the carb from the back bowl air vent.
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Just letting of the gas not applying brakes, no I don't have an air fuel ratio meter.
 
Sounds like a fairly serious build, and would be perfectly normal. A cam in the .660 lift range probably has some decent duration and overlap. When you cut the throttle the manifold vacuum spikes and some fuel is still being pulled in. With the overlap and high vacuum, port reversion will inevitably dump fuel into the exhaust. If you pay attention at just about any short track, the cars are always running flames going into the corners. This was even common in NASCAR before they switched to fuel injection, and I can guarantee you those guys know how to tune a carb better than anyone on the planet.
 
perhaps the OP could try different methods of decelerating . Clutch in, or bump into neutral if auto, or turn ignition off, I don't know. I've never run that hot a car, so I don't know the proper procedure for shutdown for this type of car.
 
I do agree that oval track cars are constantly popping on decel or even just after revving, but I never hear it on drag cars or healthy muscle cars. I've owned 2 different cars with healthy big blocks that ran in the 9's and they ran smooth as silk. I would double check the total timing as they've already mentioned, if it looks fine I'd try a buddy's carb next.
 
ProSport said:
I do agree that oval track cars are constantly popping on decel or even just after revving, but I never hear it on drag cars or healthy muscle cars. I've owned 2 different cars with healthy big blocks that ran in the 9's and they ran smooth as silk. I would double check the total timing as they've already mentioned, if it looks fine I'd try a buddy's carb next.
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Yea I'll check timing and make sure there are no vacuum leaks, then I'll check the carb. I'm really appreciating all the responses trying help.
 
Here it comes.....T-port sync.
This is same as late timing and butterflies too far open dumping fuel on decel which then continues to burn in headers and if oxygen found there,explodes. Catch it early/save a muffler.
 
Its nice when a thread ends with the op actually getting back and verifying the fix.
 
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