I need some help, I recently installed an HMF balance slip-on, K&N filter kit, and rejetted my carb on my 07 trx450er. Now it cranks way better than stock,no choke, cranks right up. However the problem is, it backfires occasionally on startup, runs smooth and real strong, but if I run through the gears and suddenly stop, it sometimes shuts off. It cranks right back up, but It's agravating having to keep cranking it. Any help would be highly appreciated. Thanks
Marty

 

Am I the only one here thats ever had this problem? Anyone?

 

well i would say you put the wrong jet in. is it poping? or kinda powing? the diferant tons in the backfire will tell you if it's lean or rich. check you plug. see what it's doing.

HR

 

Spend the money to have it jetted by an experienced professional!!!!

Jetting is more art than science. You can't just buy a jet kit and throw in the jet they recommend and expect it to be perfect, you have to jet it by how it rides, and that takes experience.

To start with, you are way to rich on the bottom seeing it starts without any choke (I don't think I have ever seen a 450 that will cold start without some choke)! You top end jetting may be off too. Be sure it isn't lean on top, because it will run hot and that can damage the engine.

 

and one other thing get rid of the k&n before you ruin your engine and won't start at all, replace it with stock for now or a foam filter.