backfire issue

[hillbillyhpower]

just put hrc kit in my 08 450er, adjusted carb as instructed, once it is hot, i hit the button in neutral it immediately backfires and keeps turning over then starts. what do i need to adjust to eliminate this backfire everytime i hit the button? somebody gotta have some input, is it the air fuel screw, or accelerator pump setting?

[Ginxd00]

Under Boss,
You sure you didnt jump a tooth on the timing? Just a thought, sounds like too much advance maybe. I'll call ya on my 6 hour drive to the promise land.

[chad502ex]

hmm... it could be improper cam timing, but its running....

simply check that your head pipe nuts are tightly secure to the head...

a leaky exhaust at the head pipe will cause it to backfire..

does it spit flames out the exhaust tip when you go WOT then let off quickly?

[hillbillyhpower]

first off it runs awesome. the only time it backfires is upon hitting the button, and it is a blue flame out the end. does everyone with the hrc cam go two turns out on the air fuel screw? i dont think it has anything to do with the head pipe.

the timing shouldnt have changed, the chain never cam off the sprocket, as it was zipp tied to the frame right away. with the stock carb settings and stock cam, it would fire so fast you would barely hear the starter engage. no lie:huh

[Colby@C&DRacing]

My wifes 06 used to do the same thing. You have the fuel screw set to rich. This atv like to be lean on the bottom to start.

[hillbillyhpower]

so whats my move from here? from standard setting

[Colby@C&DRacing]

turne the fuel screw in 1/2 turn at a time until the backfire goes away

[hillbillyhpower]

thanks buddy i will try!!

[Colby@C&DRacing]

No problem I have had alot of experience with this issue

[chad502ex]

i still feel its either your head pipe nuts are not fully tight causing a air leak to be pulled into the exhaust.... when the air is pulled in at the head the unburnt gasses will self ignite and cause a flame to spit out the tip of the exhaust..


another thing that causes backfiring to occur is a leaky valve or a lean pilot jet....

when the throttle is WOT then released the engine is still rotating at 10k rpm,... so the pilot is meant to provide the engine with fuel as the engine spins down to idle. if the pilot is too small and lean condition occurs causing to ignite before its suppose to .....

an air screw is only good for adjusting the A/Fr for less than 5% throttle..

[hillbillyhpower]

i do have a small leak at the silencer connection, but i ran the screw back into the standard position and it hasnt backfired on ten tries. it does still rotate a turn or two before firing up, but im not sure it will get better. i hate to keep leaning it up to get the button bang deadengine holeshot, dont wanna damage anything.
thanks colby, i got concerned about loosing the snappier starting.

[hillbillyhpower]

well i kept trying and it seems to work, now is there any chance it is too lean at idle? thanks for the help, and patience:D