I inherited my Dads model 30 that I gave to him as a Christmas gift years ago, it had sat for a few years and was pretty gummed up. I put about a cup of Gumout carb cleaner in the tank and primed it a few times then cranked it up, I shut it down as soon as it started. I waited another day then drained the tank, put in another cup of Gumout, primered, started and shut it off again for another day. The next day I drained the tank, then put about a cup of mixed gas and Seafoam in it and started it up and after about 2 or 3 minutes of smoking it was running like new. I drained the tank again and ran mixed gas the rest of the season, never did change the plug and it's on it's second season now with me.