drewEllis4

So, this problem has gradually gotten worse in the past year. My wife would ride her bike and it would randomly stall. It would start up again, and she'd continue riding. But this year it's gotten much worse. So I went through the double shooting in the manual and started crossing stuff off. Got down to the carburetor issues, and so I removed the carb and cleaned every jet, and passageway that I could find. Carb didn't actually look too bad, but I cleaned it all anyway. Put it together, and the problem persists. So the next item was valve clearances. This has been a problematic issue on these bikes and I've shimmed the valves numerous times over the years, but about a year and a half ago, I installed a new head off of a 2007 crf250r that has stainless steel valves in it. But I checked my valve clearances again, and they were off slightly. so I put them back to spec, and that didn't solve the issue either. So the last item on the list was the top end (piston and rings). So since I regretted not putting in a new piston and rings when I replaced the head a while back, and the piston etc is still original I figured that regardless of anything, it really should have a new piston etc installed anyway. (this is my wife's bike...pretty low hours ..maybe 10/year.. so I figured it has maybe 120hours on it of light riding....so figured it'd be best to do anyway). So I installed a Vertex piston and rings and new cam chain, and put it back together, and the problem still persists. Then I figured that maybe the spark arrestor (aftermarket FMF Q2) could be clogged with carbon, so I installed the old but never been used original exhaust system, and that changed nothing. So now that I feel I've really tried everything, I'm really running out of ideas, I've taken it to a very experienced machanic and he figured there's gotta be a plugged spot in the carb, so he took it apart and found nothing. Problem still persists, and now even the mechanic can't figure out what's causing this issue. Any help would be greatly appreciated.