Well, if it has a very low compression you might want to get it pinched or rebuilt. A worn motor does not idle as well as a motor with decent compression.
It does sound like your clutch is engaging too early, soft or worn clutch spring could be the problem.

One thing you might want to try though is turning your clutch shoes around to leading engagement instead of trailing engagement. This will raise the rpm the clutch engages at.
So instead of:
(
. ) counterclockwise rotation

You will have
. )
( with counterclockwise rotation

If that made any sense...


If that doesn't help, I say you get a new clutch spring.