I am taking delivery of my new 07 YZ450F this Tuesday. I traded my 06 WR250F. I was wondering about what I need to do to make the YZ USFS approved. I do not want to cause a fire this summer. I know I see a lot of MX style bikes on the trails and am sure that at least half of them are not set up with spark arrestors and other proper equipment. I saw a spark arrestor cone on the Yamaha website as an accessory for the YZ for like $35 or close to it. My question is can I get one of these and be o.k. or do I need a new slip on exhaust? I do not worry about the power loss too much because I am just getting off of a 250F so the 450F will probably kick my backside.