I have a Honda Harmony mower I bought from Home Depot in 2005. Has been great until last weekend when it would run for about a minute and start sputtering and backfiring alittle and then quit. Usually after I choke it, it starts right back up and goes through this cycle. I have drained all gas from the tank and ran the carb dry. Put in new gas from a different can, cleaned the plug (had alot a carbon on it) and the air filter is in good shape. I blew out the fuel line from the tank and then blew out the fuel line from the cutoff valve to the carb. Any suggestions on what to do next. Thought of getting a new spark plug but wanted some opinions first.