MTD racing mower with parts machine

Have 2 twin MTD riding tractors, we put a larger engine pulley on the one to make it go fast, and weights on the rear wheels to keep the spinning down. The transaxle blew up after too many drag races and wheelies. The engine ran good when it happened but hasnt been started in awhile, will need a new battery. Transaxle and engine in the parts tractor are good just dont have the time to mess with them any more.