I had this exact same problem. Pull the plug, it won't be fouled but the porcelyn around the electrode will be cracked. Replace the plug and it should fire right up. If that is not the case I would check out the coil and look up in the inginition box for loose wires. Also, shine a flashlight in the spark plug cap and look for rust on the transfere cap. A big reason CR80's die is mainly because of washing the bike with the tank off. If you have you probably have a rusty coil.