my 440 is bogging @ 1/4 throttle

[440exnacsracer]

the other day, i was ridin, and all was doin well then, i went into a turn and gave it gas and it just bogged @ 1/4 throttle. it was also smoking alot, but i have brand new rings and piston, and i also heard a slight, fast quiet clatter in the head of the motor i changed the spark plug to a dpr9z and still the same. i was thinkin it was one of two things, either the valves need adjusting or there is trash in my carb. i was leaning towards valves because of the clattering. has anyone had this problem and could someone tell me if im right?
thanks

[ESR250R]

a kid i know had the same problem with his but it was putting out blue smoke. he had run it too lean and blew his motor twice on his 400ex.