Popping on decel

[Eviltanker]

I know I'm running lean but, why is it popping on decel?

[Brehmmotorsport]

alot depends on your exhaust. I pop on throttle chop almost everytime if I am wide open because I run the tc exhaust. My jetting is actually a little rich. Just a suggestion.

[Eviltanker]

HMF sport s/o. My plug is showing lean since I put the powerwing in it.

[Pappy]

Originally posted by Eviltanker
I know I'm running lean but, why is it popping on decel?

Try tweaking your air fuel screw. Slight popping on decel is usually a sign that your really close on a good jetting set up.

[Eviltanker]

Thanks Pappy, I'm picking up an adjustable needle tommarow.I will also adjust the air/fuel mix. I hope that will fix it.

[dariusld]

Popping is also a sign of an exhaust leak.

[GPracer2500]

Slight popping on decel isn't anything to be concerned about. It's when it becomes a really loud and annoying machinegun-like sound that it should be addressed. A "perfectly" tuned pilot circuit will often exibit some slight popping on closed throttle decel from high rpms.

Popping does indicated a too lean condition, but the circumstance of decelerating from high rpm on a closed throttle creates a temporarily lean state. This is how your pilot circuit can be spot-on AND lean at the same time. Well, not at the same time, exactly, but spot-on when the engine is doing one thing (accelerating) and lean while it's doing another (decelerating). There are a variety of circumstances when carbs create temporary lean and rich conditions. Wacking the throttle open from idle creates a temporary lean condition (a really bad one--this is why many carbs have accelerator pumps). Chopping the throttle from WOT to just shy of WOT creates a temporary rich condition. Decelerating on a closed throttle creates a temporary lean condition. And there are probably additional circumstances where the particulars of a specific running condition causes wacky fueling.

These things happen because of fundamental deficiencies in how carburetors work. They depend on vaccum signals and differential air pressure to deliver fuel. Certain engine running conditions can get those signals out of wack and the result is too much or too little fuel being delivered. There's really nothing that can be done about it (short of switching to EFI)--it's just the way carbs work.

Also, like dariusld said, popping on decel can be caused by an exhaust leak.

[Eviltanker]

To answer dariusld, there are no exhaust leaks. The bottom seems to be good and the top was also pretty good. the middle was a little off( throttle wise.) The guy that helped me with the jetting(from Boyesen) said You pull the most power from running the thin line towards the lean side.Is this true?

[Roman]

That is true, however the leaner you go the hotter the motor runs, the lower the life of the motor. Find that perfect, lean, most powerful jetting and then go one clip position, jet, 1/8 turn, whatever richer. Your motor will thank you :O)

Of course this doesn't apply if your drag racing and need every 1/1000 of a second to pay the bills. If that isn't the case, run it a little rich and enjoy the rebuild free ride. Just my .02

Roman

[Eviltanker]

Thank you everybody for the info. I'm going to tune it some more and try to get her perfect.