For the past two years I have owned a Scag 36" walk behind with a 15hp Kawasaki. I have had to take the machine to the shop 3 times for clogged carburator issues. The same thing comes back as the cause, some kind of vasaline like gel in the bowl that gets sucked into the carb and clogs it. I've been told its from old gas but the fuel in my tanks this last time was less than one week old. What is this crap and is there something I can add to the fuel that will get rid of this stuff or prevent it from happening? FYI, the gas we have around here has up to 10% alchohol mixed into the gas. Could this be doing it? Also, I don't know if its related but my engine revs up and down while its idling, not a consistant rpm. Is this related? What causes it and how do I fix it?