Hey guys I apologize if this has been covered elsewhere but I couldn't find another thread where someone had my exact setup. I have a 2011 yz450f that is all stock other than a recently installed k&n filter and a yoshimura rc-4 slip on. I took the spark arrestor out at the track today and noticed (maybe it was just me) that the bike took a couple extra kicks to fire. Could the pipe w/o the insert and filter of leaned it out too much? I've read the stock map will compensate for quite a bit. I was going to contact Tokyo mods about tuning my ecu if necessary. Bike feels more powerful on the low end for sure and runs great. I guess I could always do a plug check but basically I wanted to make sure I'm ok for right now on a stock map. Thanks for any info this site has been an excellent resource.