Hey all, been lurking here for a while decided to register. I got my first thumper a few days ago an having some issues. I took it on trade, knowing it needed a few things, new hot start cable, valve adjustment, plug, clutch cable adjustment, chain adjustment, changed oil, and took it out for a test. Noticed it had a stumble in 3rd and 4th at high rpm, so I started playing with the fuel screw. Found it to run best at 1 3/4 turns out but still has the stumble. Bike starts good, for a 4 stroke. Pills hard first, second, and bottom or third, but high rpm third and forth have a weird stumble them pick back up. I got it out on pavement and if I go wot in third or forth it feels like I'm feathering the clutch lightly then re-engaging. Can feel a slight vibration too when it does it. I'm pretty sure it isn't a carb tuning issue because it runs great and will rev to the limiter in lower gears. I pulled the clutch cover and all the plates for inspection. All the plates are within spec, so are the springs. Boss looked ok, the clutch housing has some scarring on the outside of it. I changed the fluids with yamalube 20-50, I do not know what previous owner was using but he said it had the stumble before he gave me the bike. I'm afraid this is leading to splitting the case, it is 10 year old bike. Clutch doesn't stink, get hot, I even tried putting it in 4th, revving it a bit then engage the clutch to see if it would slip but no slip just stall the engine. Chain and sprockets look good, I'm stumped. I've been told clutch can still be faulty even when the parts are in spec. Help!!!!