Hello there, I have a n mtd 13/96 ride on mower which starts and runs fine but will not move either forwards or backwards .I have replaced both belts but no joy so far I am inclined to think that it is the double pulley that is at fault,as there is no means that I can see of adjusting the tension of the belts , it used to work fine then I came to it one day and no go ,the belts appear to be slipping and I get a burning rubber smell after a short time, any help appreciated