My 80cc semi automatic wont stop reving to much ?

[Riley]

When the bike has been riden and is fully warmed up, in neutral when i rev it, the bike seems to carry on reving up on its own and takes a while to get back to normal tick over rev. Iv played around with the idel to no avail.

When the bike has just beeen started up and is cold/just warming it is fine and revs fine.

Any answers, thanks, Dan.