Black carbon fouling deposited on the firing-end of the plug,when this become serious,it may cause misfiring,
Cause:carbon fouling is ususlly the result of an overrich fuel mixture,misusing of chock,clogged air filter,too much oil consume,related ignition timing,long time low speed operation,the plug used is too cold.
Action:inspect the output voltage of ignition coil,unloaded output voltage exceeds 20KV,installing a hotter type of spark plugs.
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