Small Engines (Lawn Mowers, etc.): problems with spark plug in Craftsman rotary lawn mower, champion rc12yc, spark plug

Question
Hi,

Since last year, I am having recurring problem of the spark plug (Champion RC12YC)getting burned out at least twice evry time I set out to mow my yard.

Will appreciate possible reasons and the solution. I take care to change engine oil, prepare mower for winter, clean air filter etc. etc. but unable to come to grip with spark plug problem and any help would be greatly appreciated.

Answer
Send me the mower model number so I can look up the engine spcifications.  

Does the spark plug have black sooty looking deposits on it?  Have you tried using NGK brand spark plug?

Send me the mower model number, xxx.xxxxx, so I can look up the engine.

Eric