Have you checked to see if the flywheel firing at right postion.Top Dead Center.May be the dial key has came out and its not firing at the right time.I had this happen on 87 lt250r i bought off my friend.It would want to start and then we pulled it it would almost run.Like it was super rich.But it was the flywheel not firing at the right time.Bought a key and put the flywheel back on and it fired first kick.But you need a flywheel puller  to pull the flywheel off.Unless it has spun on the crank from not having the key.Just something to think about if nothing else work that you do.