ok,there are two reasons that a plug will get fouled up.
1,There fuel air mixture is too rich this is a problem caused by a blocked air filter element or possible a loose jet in the carb,also a maladjusted needle float or badly seating float needle which will allow excess fule past it to be burnt.
2,The piston/rings and /or bore is worn or damaged and letting oil into the combustion chamber or possibly the valve stem seals are leaking.
as a general rule the way to tell the two problems apart are as follows.
if the plug is dry and black it is running to rich and if its wet and black its getting swamped with oilA n engine that is burning a little oil will make the insulator nose on the spark plug get some white deposits on it though.
To summerise the reason it stops running is because the white ceramic insulator nose is getting covered with carbon and therefore loosing its insulating properties which in turn sends the sparks energy straight to earth and does not produce a spark at all.I suggest firstly finding out if its dry black deposits on the plug or wet.from there you will have to get the work done to rectify it.any more questions just ask one of us on here we will always help you out.
adam bike doctor
December 2009
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