Bike jaults forward when put in gear and stalls!?

[LAURAPOTTS]

Has been standing in garage for a couple of months now, runs fine but when put in gear will snatch forward and stall ,also unable to push bike with clutch lever pulled in when in gear.Could it be clutch plates sticking? how do I fix?Thanks
Thanks for help so far as for the bike,its a 1981 cb750.Has had new clutch plates 2000 miles ago, and has been fine until left stood in garage,but there has been a rattle coming from inside the front sprocket area before the clutch problem,even when bike is not moving the rattle is still there!

 

[RichardD]

Definitely sounds like "clutch drag"

Normally this is due to a stretched cable, if it is a cable operated clutch, or lack of hydraulic fluid if it is a hydraulic operated clutch (very rare on motorcycles).

Is it a wet clutch or dry clutch?

If it is wet (probably on a 2-stroke engine), you would need to change the engine oil. If dry, shortening the cable until the plates are free should solve the problem.

NB the plates should be completely free only when the lever is fully operated, and the clutch should start to bite after only a small amount of release movement.