Help Needed df250rtb

First time poster out of desperation. Picked up this project and love the bike. It sat in the weather for some time by previous owner and I’ve had to repair or replace a lot on the bike.

Old carb was eroded too bad to repair so I replaced it. New spark plug, coated fuel tank, new filter and lines, etc. It starts right up, idles like new, revs to half throttle great. After installing and adjusting a new clutch cable it shifts great through the gears.

Problem: it has a terrible miss above about half throttle. Maybe 4K rpms (guessing). If I shift when it starts to miss I can roll into fifth and it will go about 40-43mph and that’s it, it’s just sputtering and popping. Back down to 38moh and I could ride all day with no sputtering and popping. New carb, float seems to be set right, air screw adjust makes no improvement at all. Thought maybe valve adjustment. The exhaust valve was tight so I set it to slide .006 and hold .008. Seemed to smooth the idle a tad but made no difference in misfire or backfire. I’m at a loss, don’t know where to look next. Shooting from the hip maybe: coil, stator, cdi? Maybe burnt valve, but I don’t really know how to check or diagnose? Any ideas? Here’s a video:
https://m.youtube.com/watch?v=9oG1mL...ature=youtu.be