If car will start and not move off with clutch floored, but attempt to move off if started without clutch to floor, then its probably not the clutch.
It could be the gear linkage. On the 899 its only two cables, one for up and down, and one for across. Check that these are not fouled at the gearbox end. It may be beneficial to remove the airfilter housing to see the box more clearly.
Cheers
D