My son has a moto 4 250 that the starter clutch went bad on. The bolts sheared off that holds it to the flywheel. I managed to get them out and replaced the clutch and bolts no problem but I did notice that there was a small amount of metal debris stuck to the pickup/stator from the sheared bolts. I wiped that off and put it back together but now when we try to start it will turn over then kick backwards hard like it's firing to early.
It will run if it starts before kicking back but won't idle you have to keep it revving. Could the metal shavings done something to the stator to throw off the timing? I did check the cam and crank marks and they line up as they should. It is much worse if we open the throttle up any.

 

You probably pushed the key out of position when fitting the flywheel, if the flywheel isn't on the key, the ignition will be out of time. Re check the cam timing afterwards as this will be out if you set it with flywheel off true TDC. Other possibility, the bolt heads hit the stator and bent it.

 

I did check the woodruff key again when going over what the problem could be. After posting this we rechecked everything and recleaned the stator and pickup. Everything is where it should be, it only kicks during startups. Once it starts it runs great except for the idle. We have a rebuild kit for the carb next. I have a video of what it's doing but I can't upload it here. Don't remember if I mentioned that with the kill switch off it will crank perfect but as soon as you turn it on it starts kicking back.

 

Had a Suzuki 750 doing this, took a while to note that with plug lead pulled it turned over fine. It didn't kick back, just stopped the starter dead when coming up to TDC, so must be ignition out of time right? Wrong, as soon as I pulled the alternator case I found the problem, there was an idler gear between starter motor and one way clutch, and it's bearing bush had disintegrated.

 

Well I think I fixed it. I took the stator cover off again to really clean it up in case there were any metal bits left and there were a few stuck to the back. this time I unplugged the stator to work on it on my bench, first time I just moved it aside. I noticed that someone had messed with the plugs before( I failed to mention we had just got this atv) and one wire came right out of the socket. Looking closer i noticed the two wires from the pic up looked crossed like they had been pulled out before and put back in the wrong slots. I pulled the other one out and put them back the way they fit better and plugged it back up. Put the cover back and it starts right up now, runs great.