Im having a bit of a problem with my 670 Summit. Its a 1996. When Im revving at about 6000 + rpm I get a slight sputter and can feel the engine loose a bit of power. Does this sound like I need to make a needle adjustment on the carb slide? They are Mikuni 40's. My plugs are looking great in color so Im dialed in on my main jets. But this slight sputter at high rpm's is bothering me. I need to have her pinned and running smooth. Any suggestions would be greatly appreciated.

You probably could move the clip. Go down one clip position first though just in case it is a lean condition you have now. If it gets worse then you can make it leaner by moving the clip towards the top of the needle.