If you mean the opposite, ie. that it stalls when the clutch is disengaged, (pulled in), then the idle screw might need to be adjusted inwards, (clockwise), to raise the idle.
Regarding the 'spotty' running and bursts of speed and deceleration without your 'consent', this sounds a bit like a lean mixture, possibly due to an air leak where the carb attaches to the inlet tube, or where the inlet bolts to the barrel.
A guess only, but not a bad place to start. There are several ways to seal it, but temporarily, Permatex non-hardening sealant smeared on the carb/inlet joint during assembly works. If this proves to be the problem, a search will find the various methods of sealing.
... Steve