Hesistates in 2nd & 3rd

[mmiiimp5]

I am having a problem with my 04 400 ex hesitates when i go WOT from a low rpm in 2nd and 3rd. I just put on a K&N, 2in exhaust insert, bumped the main jet from a 148 to a 152 and turned the fuel mixture screw out about 1/4 turn, can really feel the power difference but now if i let the rpms get to low in 2nd or 3rd it hesitates for like 1-2 secs then takes off. I did the spark plug check and it gray on the top of the insulator and dark brown on the sides. should i move the needle down 1 knotch? got any other suggestions.

Thanks for any help

[mmiiimp5]

forgot to add i took off the air box lid off too

[underpowered]

sounds lean to me, has to let the fuel catch up before it will go. try lowering the clip on your needle (actually raising the needle up) one or two noches and see what that does,