I've been reading tons of threads on bog and surging but I'm still confused on how to diagnose my problem. I just got my '06 YZ450 back to Mexico and broke it in yesterday. With stock jetting it seemed to have crisp response when snapping the throttle but with tons of popping on decel. So today I changed to the 48/170 as recommended and the popping was much better (though still there a little) but I'm now having problems where it bogs (to the point of stalling occasionally) if I snap the throttle open quickly. I didn't notice this yesterday. What's even worse now is that the engine doesn't want to run steady in any gear at 1/4-1/2 throttle without surging/cutting. Should I keep the 170 and go back to the 42 pilot? Should I try a 172 to totally eliminate the popping or is it enevitable? Should I change the clip position? The surging at a constant 1/4-1/2 throttle is my biggest problem as I can live with the little bit of popping. What would be causing this. Oh, I also added a zipty FMS and played around from 3 turns out to all the way in and didn't notice a big difference. BTW- I live at sea level and it's about 70 degrees. Thanks!