Ok, (and back me up on this Bob)! The up and down RPM is caused by the Governor action! The action of the Governor is to speep-up the engine RPM, as the load requires it! The first thing you want to do, is check to see if you have a full tank of gas, then, pull the carb. float bowel, and run a small wire, (or a welding tip cleaner will work), thru the main jet, to see if it is not plugged. Also, make sure the Carb. bowel is clean from anything that may float within the bowel, and clog the main jet opening, in an intermittent manner, when the engine is running!
Wayne
edit: to make spelling gooder !!! Lol