Dirt bike question please answer!?

Question

i have a older YZ80 today i went to start it and it started fine but stalled, i go to start it again, and it wont start and it backfires, what it wrong????

Answer 1

Check the plug first as someone else said as it is easy, but it could also be out of time.  You may have sheared your woodruff key on your flywheel.  Its usually located on the left side of the motor under that big round cover with the wires going into it.  Its a big heavy magnet and when it gets to the proper position it sends the spark to the plug.  It has to be in the right position to fire at the correct time.  Their is a slot cut in the shaft and the magnet that is kept in line by a small device called a woodruff key that looks like a half moon.  Backfiring is often a sign of timing problems.  If the nut that holds it together came loose or something hit the flywheel that key is suppose to shear to protect the shaft.  Look up a parts fisch for you bike.  yamahaoftroy.com has them.  Also Yamaha calls the flywheel a rotor I think.  The bad thing is the rotor and shaft on in different pictures

Answer 2

could be your reeds

Answer 3

Check for a fouled spark plug.