I own a 1992 nc30. The engine has been recently recently rebuilt and a new clutch plates (steel and friction) fitted. With the bike is on axle stands (rear wheel off the ground) and running in neutral- if I hold the clutch in and select 1st the rear wheel spins very quicky and picks up more speed if I rev the engine. It will also stall the engine if I hold the back brake on. It doesn't stall when the bike is on the ground, in gear with the clutch in although it does lurch forward when it is put into gear and it difficult to change gear (going up or down) when riding using the clutch. Like it dosen't want to go into gear unless there is a lit of pressure on the gear lever. Changing up without the clutch is fine tho. I've tried replacing the whole clutch with a spare one (which I know is ok) but doesn't seems to make any difference. The feel at the lever is good and when I look at the clutch without the crankcase cover the lever operates the pressure plate ok- it moves out by 3 or 4mm and the creates separation between the plates, although they do stick together in groups (which just seems to be the friction of the oil between the plates) Changing the actuator made no difference. I'm using motul full syn 7100 oil.

Is it definately a clutch problem or could it be something else? Any help is much appreciated-

it could be the fully synthetic oil that your using.....
ive heard on the forum that its best to use semi synthetic as fully synthetic causes problems with the clutch.
it is quite normal for the rear wheel to rotate whilst off the ground even in neutral but maybe not as much as you have experienced.

Who did the replacement of the clutch? The stack height sounds like it is too talla nd causing drag. The oilis not the issue, it would slip more if the synth oil is not behaving.

The clutch pack has to be within a specified height - check the Haynes for this and whip the plates out and measure the thicknesses to ensure this is within tolerance.

My clutch will drag a sniff when the wheel is off the ground, revving it in neutral causes the wheel to rotate but not enough to stall it if I hold the wheel steady.

have you checked the cabling too - might be the easiest option - is there any slack at the bottom of the cable? You could adjust it out a touch and then oince it has bedded in and worn down it might get better?