YFZ 450 low end studdering, problem

[bansheerider98]

my ro has a new 07 yfz 450 and when he rides it at a lower revv it kicks and sputtrers, like 1/3 revv to 1/2 revv it does it. so whats wrong, or is that normal, and woud a pipe /header and new intake help at all>?

P.S. recently jetted to the weather conditions, so probbbly is not the problem.

[YFZ450 11x]

I know you say you rejetted but it sounds like your needle