engine trouble?

[motophreak]

hey guys
ive got an atomik 125cc (lifan engine) that im going to sell soon but i need to get this problem fixxed before i can sell.
When i get just over halfway in revs, the engine starts to rattle and i start to lose power before releasing the throttle till it stops .

I had been having trouble with the clutch, it wasnt fully engaging but i adjusted it and thought it was okay. So what i want to know if the clutch can cause this or its something like valve bouncing, and how would i fix it?
ive done my valves but it hasnt really made a difference.
one last thing is if i screw in the clutch cable tensionor fully (clutch cant engage) it seems to make a difference, this is why i have a feeling its something to do with the clutch.
thanks

 

[FMX_22]

Are u sure u tightened everything uP??? Could be rebuild time if the motor is knocking how meany houres has it done???

 

[motophreak]

bought it halfway through last year, done probably 20-30 hours or so, guess its about time to do i rebuild then..

 

[sean01]

maybe a video might help in here mate... the description is a little hard to follow

 

[motophreak]

yeh its really hard to explain...its a bit like this vid YouTube - 140cc pitpro valve bounce, but mine only happens at higher revs.
i'll try get a vid of mine.

 

[sean01]

so many things can cause similar problems..

bad carb tune
bad fuel
bad ignition (cdi,coil stator)
plus more...