engine running on?

Anyone experience what appears to be a stuck throttle,but only when the clutch is in?
Of course I suspected the carb slide but it seems to be working fine.The twist grip snaps
right back.When I come to a stop with the clutch in the engine speed almost seems like it's
accelerating but if I let the clutch out just enough to put a little load on the engine the revs. drop to idle and stay there.This is not a new engine.Dax 70cc. with 2000 mi.on it
While I have your attention let me throw in another one.My top speed is about 32 MPH with
40 teeth.At 26-27 MPH it's very smooth all day long,but above that it develops an intermittent hesitation.This seems to be a RPM or MPH thing because its fine at full throttle up hill.Needle clip position has no effect.I cannot detect any obvious air leaks checking with starter fluid.I'm hoping
its not leaking at a seal although I don't see any signs of that.Thanks,Ron
I should add I ruled out coil and plug.

i think they all run like that,i know mine does.
they just need a little fine tuning and adjustments here and there.

Well my first engine had that problem,but it's new to this one.I'm wondering if it might just be insufficient fuel flow.I may try an upgraded petcock.If that doesn't do it I may bore out my jet a few thousands.From what I understand the needle has no effect at full throttle as its pretty much all the way removed from the jet.So you're relying solely on the jet size.Can anyone verify that.Ron