I bought a "STOCK" 08 TRX450ER and I have trouble with it under cold temperature (Winter). It seems to run too lean on the main jet and the engine is struggling in 4th and 5th gear on torque... well it has difficulties to get RPM!! My dealer told me to adjust it with the air/fuel screw but I tried both direction and nothing happened.

Which size of main should I use?
When you turn that D shaped screw in (air/fuel screw clockwise)... is it leaner or richer?
Maybe a warmer plug would do the trick?

Help please!!

Ok I'm not a expert on this I'm going to say with stock jetting adjusting your air fuel screw is only good for 0-1/4 throttle responce, cold starting, engine decel, your engine is set lean from factory so in winter it is really lean,bumping your main up a couple sizes is definstly a good thing especially if your loosing top end performance.... Stock I think your at a 118 try going up to a 128, I'm up to a 170 main in winter with below freezing temps, with air box lid removed, and full exhaust....

Good luck! Andrew

Good thanks... I'll try it. I didn't new that screw was only good for 0 to 1/4 throttle!

be careful when setting the air screw. when your tighting it,just go till ti lightly seats, don't crank on it like a gorilla. also if you back it out to far it comes out in your hand.