Well for one my cousin and i rode it wayyy to hard when it ran--doing jumps, flipping it, hit a couple trees ACCIDENTLY--but it still ran after that. The thing that did it was one hot summer day we went riding like 10 hours nonstop and we were riding it hard then too. we also took it mudding with water almost over the 4-wheeler but it ran strong the whole day. It wasn't until the next morning when it quit running. It would turn over and it had spark, fuel, oil but then all of a sudden it just locked up so i tore the motor down and found out the piston was stuck to the cylinder so i got it un stuck and i took a break for a while. While i was taking a break my step-dad tried putting it back together and put the jug/cylinder on backwords and broke one of the tabs off the jug. Oh yeah the rings were fried also so know i need a new cylinder and rings. I just hope i remember where all of the parts go. its been two years since i took it apart.