Motorcycle Repair: fouled plugs, stroke bikes, excessive smoke

Question
My son has a CR80 and keeps fouling plugs, even hotter ones. Can you tell me why?

Answer
Hi Joe.
 Are they oil fouled or fuel fouled?  If they are oil fouled, then it could be oil seeping past the rings in excess amounts.  Excessive smoke combined with oil loss from the engine would indicate that.  Oil fouling could also be due to the oil/fuel mix being off (common error with 2-stroke bikes).

Fuel fouling is almost always due to mixture being off.  Sometimes this is not so much the actual mixture, but something upsetting the mixture and drawing excess fuel into the carb or possibly the carb is dirty and needs a proper cleaning.
 Alternatively, the problem could be from insufficient spark at the plug.  Normally, this is because the coil is failing, or there is a ground arc or an intermittent short in the ignition system.

It could also be due to an excessively dirty air filter.

Check those and see what you find.
Good luck.
FALCON