Problems with jetting 350 raptor

[VelociRaptor350]

I have a raptor350/warrior on juice. My mods to date are a HMF slip on and k&n stock replacement filter. I installed the dynojet kit and im running the biggest jet they gave me, a 140, with the screw out 2 turns, and i have a problem with backfiring off throttle.  Like it actually shoots flames out the pipe, it looks super cool, but i know that its got to be hurting something.  Ther kit suggested a 138 with the lid removed, i have the lid on and im having this problem, what do you think i should do to cure the backfiring.  It also has a problem idling, it always stalls out.

[Hoosier Daddy]

make sure you dont have any air leaks where your carb attaches and check your gaskets... after that i would make sure you dont have a valve sticking or not adjusted right and its allowing compression back through the valve....

[VelociRaptor350]

I thought it could be the valves because it started happening around 20-25 hours on the motor so i adjusted them and it didn't help.  The motor is new so i doubt its the gaskets, but i will check them out.  Do you think the pilot jet has anything to do with it? It runs good at full throttle but has a stumble ar part throttle. Thanks for the help, i appreciate it.

[big-daddy]

did you change the pilot jet? maybe to lean, remove the air filter and see if it worsen. like chris saided check for air leaks spray little  carb cleaner around the base of the carb and see if the ilde changes.  

[VelociRaptor350]

The kit didn't come with a pilot jet, so no.  Im going to check for air leaks and ill see what happens, Im kinda "grounded" for a few weeks because of a broken collarbone so all i have is time. Thanks

[VelociRaptor350]

I think i found the problem, the k&n gasket/foam was ripped at the base where it slides into the airbox, i tossed it.  Run's better with the stock filter/outerwear(i know its pathetic).  Thanks for the help.

[big-daddy]

when a eng runs lean because of the pilot jet. symptoms are popping or spitting in the carburetor as the trottle is opened. Somethimes theres will be popping or backfires in the exhuast system on the engine deceleration after the trottle has been closed. engine performance improves in warmer weather and worsens in colder weather. if you remove the air filter it will run leaner and the problem will worsen. Good luck

[Hoosier Daddy]

big daddy,

 are you sure that engines run better in warmer weather?? i think you might have typed that backwards.
I know 2 strokes love the cold, as the old saying goes "the hotter the engine the more power it losses".
the colder air is more dense it is therefore it has more of a "charge" thus your able to get more air in the chamber.
kinda like intercoolers in turbos (because of the hot air a tubro produces), ice cans for fuel, NOS has a huge cooling effect and all of these are performance enhancers.