Speedfight 2 - Possible Variator problems - advice appreciated?

My son has a speedfight 2 and recently the drive belt broke which I have replaced. I couldn't get the nut off the variator so took the clutch off instead to get the new drive belt on. The problem is that the rear wheel goes round (ie the clutch engages) at tick over speed and the bike will not accelerate when off the stand - it accelerates no problem on the stand and the rear wheel is driven at all revs. I have looked at the position of the belt with the engine off - on the variator the belt is at the outside of the variator (which is making a horrible noise when the engine is running). On the driven pulley (clutch) the belt is very near the inside of the pulley. I have a suspicion that maybe the rollers have stuck and are holding the belt on the outside of the drive pulley which means the driven pulley is turning too fast even at tickover and therefor engaging the clutch and turning the back wheel at low revs.
Any help or advice would be very much appreciated?