I have a grizzly and i was thinking i could hang with a 400 ex, well i was way off, for top end he was a little faster, but he got there twice as fast as me, manual clutches make a difference

 

I have always had good luck with NGK spark plugs in Polaris and Yamaha. Never mind about the Yamaha! Always check the gap in your plug, it is important. The manufacturer doesn't care what the gap if for that plug...it is up to you! Good Luck