My son was riding his yz250f yesterday and it quit on him, said it was hard to kick at first and then started and quit. I checked it and it started right up, but when i shut it off it stopped right now, and i pulled in the decompresion handle and turned it by hand and got a spot that was kinda hard. I tried it again and got it to do it one more time. I was thinking timing chain maybe is getting bad and kinking? Anything else? Thanks!