Ok So I ran out of time trying to fix this myself and dropped it off at a reputable mower mechanic. He swapped out with a v pulley and the mower now idels fine without the belt flipping. However after 10minuets of mowing the belt flipped onto its side. The belt was about 45 min old. Thinking that there might be some memory in the belt the mechanic then put in a brand new belt, however the same thing after 10 minutes of mowing the belt flips on its side.
The pully under seat has been changed to a V pully (this made some difference) The left drive pully got changed to a new one Has a brand new v belt.
