Well, the basics are spark, air and fuel -- if you have all three (in something approximating the proper amounts, at the right time), you have a running engine. If it's narrowed down to no spark, it's a process of elimination in the ignition chain, eh? It shouldn't be too difficult to pin down, really. Check the ignition coil, first. If it's good, check the CDI, next. One or the other will be the culprit in 98.7% of the cases, if you've ruled out a bad boot connector, already.
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