Your engines may look clean when you peer down through the pull start screen but don't be fooled. Once a year it's good to take the pull start and other stuff off the engine to expose the heads. You will be amazed at how much stuff get trapped on the heads and insulates it effecting it's ability to cool it's self. If the engine runs hot it will ruin the two gaskets and you'll starting leaking oil. Once oil mixes with the stuff built up on the heads it's hell to get it all clean.