I have a hmf ballance pro series full pipe um aluminum air box and k&N filter lid is removed on my yfz 450. I started out with a 165 dyno jet and that sputtered here and there then went down to a 160 and that was all right sputtered if i reved it out all the way and then in 5 gear when off the throttle it backfired sometimes. so now i droped it down to a 155 and it seems to run fine but i dont want it running lean and i know the stock main jet is 158 but dyno jets and stock jets read different if i understand right. some help would be nice.

 

I think you too lean. A DJ is about 10 sizes smaller than a factory jet. (165DJ=155stock) I would try a 175DJ. A lot of people are having problems dialing there 450 in with the DJ kit. So you may just want to get the NCQV needle and use Kelin jets