My 2000 yz125 won't idle and hesistates during acceleration at mid RPMs. It starts on first kick and other than those issues it runs perfect. New completely replaced top end, new Reeds and Reed valve. Any suggestions?
Idle or pilot circuit cloaked I'd think. Specially if the jetting has not changed.
The reed valve is OEM or aftermarket? I read about some sealing issues with the V-force which could also be responsible.
Have a good look at the plug, at best use a new one and see what color you get when riding "normal" for 10 minutes.
What throttle position are you at when it hesitates? Is it a bog or a miss? Likely a pilot circuit issue in the carb, likely dirt or varnish. Read the jetting link at the top of this forum and you'll have the issue knocked out quick.