Jetting

[uspatriot]

I had my air filter off and my 400 would run and idle fine, I put my k%N air filter back on and now it dose not idle. Also when i am riding and let of the gas it backfires a bunch of times, If you let off the gas for to long it will stall. Dose it need to be rejeted, what size jets should i get, i have a white bros pipe and a k%n filter? I am not sure what the jet sizes are now.

[midwest honda]

Who rejetted it for you or are they stock jets.

[midwest honda]

I had the same problem as you and i would bet that it is a rich condition and needs leaned out. And never ever run it without an air filter on unless you in a dust free environment. Meaning dont ever run it without a filter unless you like down time and costly rebuilds.

[uspatriot]

what size jets should i use?

[rob_990]

whats in it now?

[uspatriot]

stock 450r pilot jet and idk what size main jet

[rob_990]

go in second gear and rev it out then kill the engine and take the plug out and tell us what it looks like.

[uspatriot]

I think its a 48 should i get smaller or larger?

[hypersnyper6947]

In order to find out where you need to be you need to know whats in there now, so take the carb apart and tell us what size pilot and main you have, then tell us what clip the needle is on from the top. You might as well clean it real well while you have it apart.

[uspatriot]

what does putting the clip on the to vs bottom do?

[hypersnyper6947]

the needle has like 5 slots where the clip can go, if its on the top clip its leaner if its on the bottom its richer, this can help you dial it in once you found a main jet thats close.