engine cutting out

guys i've had my wb pro-meg pipe for over a month now. i've noticed it backfire alot when i let off the gas going down big hills and i seen a post on here awhile back about running to lean making it backfire so i decided i would try going from a 165 main jet to a 170. just to see if it would fix the problem. other than the annoying backfireing the thing seemed to run good. once i rejetted and got going it started backfireing again. this had me all confused. so i decided for some strange reason just to mess around and see what would happen if i went to a 160. (one jet size smaller than i started with) well i did and i noticed that i lost power and was still backfiring. so i got to lookin around :rolleyes: and i found black stuff coming out of my pipe where the headpipe connects with the silencer. could that explain my backfire problem? any ways i went back to the 165 jet that i started with and i got it back running like it should be but, when i hit on the gas and hold it open as it starts winding out the engine starts missing. does it in all the gears but only when i wind out the motor wide open. what can i do to fix it??? it runs fine other than that. could i have messed up my spark plug when i went to a 170? i need advice. if i ever get it to stop missing im not gonna work on it anymore. i always mess something up

Sounds like you are running lean. Where at in the full throttle is it missing or stutters at?? At the start of full throttle, mid , top?? Sounds like what mine was doing when first rejetted it after i put my pro circut on. Where is your needle set at?? You might want to raise your needle up one. i did that and it cured all of my problems. Also what is your plug reading?? Brown, white, etc etc........


Andrew

The missing you are hearing when it is wide open is probably the rev limiter, or if the revs are not that high when this is happening, you could be either rich or lean. Sounds like you might be lean on the main jet. With a full system like you have, a main jet higher than a 170 is realistic. I have settled on a 172, and I just have a White Brothers silencer and K&N.

That black stuff is probably caused by leaky exhaust gaskets. When you take off the headpipes and put them back on (or install new ones) you should put in a new gasket so it won't leak. That might have something to do with the backfiring, but it just sounds like it is the jetting. Your spark plug should be just fine. Try a 175, and go higher if you need to. You will get it, just don't let it get to you too much. Good luck!

If your exhaust has a leak, it will cause a backfire. Fix this first.

If it still backfires on deceleration (not giving it any throttle at all), then your Primary Jet is to small (lean). The Main Jet has nothing to do with it. When you close the throttle, you are running on the Primary Jet only.

The stock PJ is a 38. You can try a 40, 42 or 45.

Yep, I agree with Rico...

First make sure that exhaust is sealed at the head. If not, you could warp your exhaust valves as well as have that annoying backfire. Just make sure she is good and sealed...

Eric

its missing at the top end of full throttle. how do i know if its the rev limiter? the black stuff on the pipe is coming out where the head pipe clamps down on the silencer. and i dont see how i could be running lean when i went to a 170 main jet it burnt my plug black.

Strat:

I would recommend going back to a 160 main jet, that should be very close with air box mods. As for your backfire, lower the clip on the pilot needle one notch and turn the air/fuel screw out about 2 or 2.5 turns. From the way it sounds you might need to tighten the clamp more where the silencer meets the head pipe.

When you hit the rev limiter it will have a consistent rythem to it, unlike a carb or timing problem would give you an inconsistent miss. With the new exhaust, the rev limiter will be much easier to hit than it was with the stocker.

Good Luck

thanks for the replies.. i jetted it according to my altitude. the 165 was running perfect to begin with. i just tought i had messed something up when i was experimenting with the 170. the miss is consistant and it only happens when its running wide open full throttle so i think its the rev limiter. but just in case im gonna get my friend to look at it. if anythings wrong they'll find it