Check your iginition timing. On a two stroke if it gets to retarded or advanced then the motor will seize. Sorry I cannot remember the way it happens. I found out about this the hard way on a relatively new machine. No lasting damage to me or machine but I did not skid, the Pneumat panniers and the fact I was going up hill meant I was able to sort myself out and get home. I did miss a rally at Hay on Wye however.