Anybody else's 570 sputtering around 4k rpm. Mine does and it really annoys me. Runs absolutely purrrfect until 3800 then barely sputters then clears up at 4100. Tried a ngk plug with no improvement. Seems like it leans out or something. Plug checks good visually. It had 4 miles on it when i bought it. Has done since day one. Hoped it was just a break in thing but i now have 25 hrs on it and about 150 miles. Any suggestions before i take it in. Its still under warranty. Thanks in advance. By the way, i am a newbie here. This is my maiden voyage.