I learned this the hard way with a new Tohatsu 6 that after 3 weeks on the boat refused to start. I finally gave up and brought it to the dealer. Amazingly, after only three weeks, with a tank of "fresh" gasoline, the carb had to be removed and cleaned. I learned it is a pervasive problem with smaller 4 strokes and 10% ethanol. Now I only burn ethanol free gas in the motor, run it out of gas each time I shut down, and in addition, replace the gas about every 2 months if I haven't burned much. (the old gas goes into my suv). Have had no problems since then.