i have a 2003 450 and I find that if you just gun the engine with resistance on the wheels (mud) it will bogg out an die, try giving the engine a little gas to get the idol up then hit it hard. I also some times hold the brake and give it a little gas then release the brake and gun it and these tricks have helped.

 

yeah that is what is happening when there is resistance on the wheels like mud and you give it lots of gas it just bogs oout but when you ive it a little gas it tries but it needs more gasto get going and when you give it more it bogs out. i think it is because it is running rich because when i removed the air filter lid it never did it , but i havent figured out how to jet it yet so it runs leaner. thanks for the advice, could you tell me how to jet it.