Yep the hood will eliminate the light, As long as you don't go over 48 to 50 inches wide you should be good on trails. Ahh Yes the question about the Yoshimura, Well I was flat out surprised by the RS3 full Yoshimura on a 660, It had a great tone and I noticed a slight power increase, The reason I switched to the Sparks X6 bigcore was because all the reviews and hands down its one of the best singles for the 660's and I always wanted one. In 2004 Kory Ellis ran his 660's in several national events and they dynoed 5 top name exhausts and Sparks brought the most power, But this is strictly 660 based, For the 400ex ive heard good things about the Sparks, Either way Yoshi or Sparks your gonna be pleased. Yoshimura is a damn good exhaust. Thumbs up on the ASV's I love em, If you ever decide to switch those nerfs, Get some Houser Probounce XC width, My little cousin just got some 2 months ago and Im amazed by how they feel, they have a ball in between the peg that flexes. Just a heads up right now on Ebay they are a Quadtech seat for your 400ex for 90 bucks any other time they are 145 to 170.