My 2002 scambler 400 backfires when you let off on the gas. It has a port and polish from hotseat and is two sizes over the original size. I am currently riding at around 3000-5500ft everytime you let off on the gas it backfires I have tried to ajust the air screw it helps alittle but not much. My main jet is 200, any advise would help.

 

ell, you juiced-up yer heads and bore, and now waat it to act stock?

Porting is a great idea. Polishing is only great for racing. You shouldn't have sprung for that.

Head polishing tends to pool unbuned fuel and decrease atomization/varporization of incoming fuel copared to leaving it rough, so it (fuel) is getting blown out though the hot pipe. Since you've closed off the O2 by letting off the throttle, "post combustion" happens in the exhaust system. Unless you are willing to go with leaner jets (and less power blast) you will have to live with it. Plus, leaning out the fuel mixture further on a hot motor is looking for a meltdown ESPECIALLY if you have increased compression with your overbore kit.

D

 

Try a leaner pilot jet, and let us know how it works have you called out tech line? We do not advertise that we polish anything you wuold of just recieved a port job the polish gimick has came and gone we have never offerred such a thing.

 

Adjust the throttle cable freeplay . The sending unit thinks the throttle is stuck open .

Rick

 

Thanks for the advise will try the suggestion. I got the work done last yr and it worked great! added some reeds the hsp silencer and a few springs for the cluch, helix, k&N filter then recently put on the block off kit and am currently running mixed 400ml per 20L.