Mike, When you say, "It quits firing," do you mean that you stop losing spark, or that the engine stops running?
If the plug is sparking when it is removed from the cylinder head, then one would assume that it is still sparking when it is installed in the cylinder head. Thus, I'm assuming that when you say, "it quits firing", you mean that the engine stops running. If that is the case, then you should take a look at your carbureator.
One member of the forum (RinconFun), was having similar issues on his Rincon and was about ready to push his Rincon over a cliff. But, as a last resort, he decided to replace his carbureator, and bingo... replacing his carb did the trick. If you don't ride your machine a lot, the gas can go bad (turn to varnish) and can really goof up the works in your carbureator. If that is the case, you really need to disassemble, clean, and rebuild the carbureator, as just running solvents through it (via your gas) won't do it. Also, if you have the same gas in your tank for any more than a month or so, you should put a gas preservative called StaBil in the gas. If you have older gas in your tank now, get it out as StaBil (at this point) won't turn it back into good gas. Then, take the time to remove and clean out your carb before you restart your machine.
If you are still having problems after that, let us know, but, be as specific as possible. Telling us that 'it won't fire' doesn't really tell us if you aren't getting any spark, if the engine is stalling, etc. Thanks,
Last edited by kentrda; 11-11-2011 at 02:29 PM.