Popping on deceleration

[roachey]

Hey guys new here, Anyways I got a mb165 and swapped in a stock 212 predator. Been pretty fun so far. I recently swapped out the stock exhaust for a straight pipe setup that I welded up (no muffler). When I get on the gas its loud and sounds really good but when I let off the gas i get this extremely loud popping noise almost likes its backfiring that is very annoying. I was wondering if this is just because of the pipe style exhaust or is it a carb issue and there is not enough fuel. I understand some people upgrade there emulsion tube and jets when they do there exhaust and was wondering if doing that would get rid of the problem?

Thanks Guys,
Will

 

[Phil1958]

hello roachey -

welcome aboard to OldMiniBikes! :thumbsup:

that motor is designed and tuned to run with the
supplied carb and muffler. if you change either one
or anything in between performance will change.

you've entered the world of experimentation, try
various exhaust pipe lengths, carb settings, air
filters, etc..

there are lots of guys here with extensive
experience on engine mods who will help;
i am sure.

ciao~

phil

 

[Stangrcr1]

I understand some people upgrade there emulsion tube and jets when they do there exhaust and was wondering if doing that would get rid of the problem?

Yes. And get rid of the stock airbox. Get an air filter kit for it with the main jet and emulsion tube.

 

[SnakePliscan]

Popping in the pipe

Your burnin excess feul in the pipe man, every time you close the throttle the fuel mixture gos rich cause your cuttin off the air, then you open it up again or it sucks enough air to support cumbustion and bang it burns off.

Yyou've probly got your idle speed set to high or mixture screw is rich, if you dial your carb in better an dont idle any faster than you have to you mite find it doesnt back fire as bad when you lift.

That being said lets face it were dealing with a strait pipe here and fire will pull air from were ever to live, thats the tetrahedron so if it lights off from the chamber side or the pipe end its were ever the air comes from.

You should see a 98 cube Shovel head with 8" slash cut zoomies at night, flames popin off the ends, Crackle crackle........Ii digress, later.

 

[roachey]

Ya i think the bigger jet and e tube will help a lot. I just took a rip on it with half choke and there was no popping when i let off the throttle thanks guys!

 

[Sinner70]

Welcome to the site fellow Masshole.
enjoy
:drinkup:

 

[ITSWILL]

Ya i think the bigger jet and e tube will help a lot. I just took a rip on it with half choke and there was no popping when i let off the throttle thanks guys!

This seems counterintuitive to me. Usually popping on decel means too much fuel.

Im with Snake on this one, I would think you need more air.

What kind of clutch do you have?

 

[C9H13NO3]

When you're letting off the gas (closing the butterfly) you're creating a vacuum. That vacuum is pulling fuel into the chamber and not all of it is being burnt- so it combusts as it enters the exhaust pipe.

If your pipe is short enough you'll shoot a small flame out if you time it right, from what I've learned from others and my own experiences, its completely normal.



Also, add a more free flowing air filter. If you're gonna uncork its ass then you should shove some more air down its throat.

:thumbsup:

 

[ole4]

an air leak at the pipe to head joint will also cause popping on de acceleration

 

[naterater]

on my pred i cut the shotgun pipe down to 7" so it wouldnt hit the frame on my mbx 10 . yeah it pops , lol but it almost sounds like i got a cherry bomb on it .

 

[SnakePliscan]

Fires plug every revolution

Wasted spark on the overlap, sparkin the plug when both valves are open, or maybe im jus makin this shizit up.

 

[65ShelbyClone]

When the throttle is closed abruptly, the mixture spikes rich and then slopes back to baseline as fuel is pulled off the port walls under high vacuum.

Popping on decel is a common occurrence with motorcycles after making airflow mods like exhaust. Many attribute it to a lean mixture and over-jet to compensate. The catch is that when the throttle is closed, fuel is being pulled through the idle circuit, not the pilot and/or main circuits if so equipped.

What the mixture does under load is what you should be worried about. Popping on decel in and of itself is an unreliable indicator.

 

[MoTo-BunnY]

an air leak at the pipe to head joint will also cause popping on de acceleration

+1 My Honda CB500 motorcycle was doing that until we welded up a crack at one of the exhaust flanges and used a new gasket.