Our sears (craftsman) 5.5hp mower did the same thing last year, it started running rough suddenly and then quit and would not restart, 2 years old and always run on premium gas. Sooo....I did the usual checking of spark plug and air filter/fuel line etc...all fine, so I took the carb off....cleaned it all out and took it apart, put it all back together, adjusted the governor for some more rpms and power like the pre-Californized mowers run at....and tried again, puff of smoke and bam, was running strong and steady...in fact better than it ever had before! It must have been a dirty or clogged carb. I also switched it to Mobil 1 Turbo Diesel Truck Synthetic 5w40....runs great on it.

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