looking from the back side of the engine, find the carb. now looking on the top of the carb find the throttle valve. there will be a screw that when turned in, highers the idle, and turned out lowers the idle. you need to pop the cover off the screw (weird) and use a phillips head screwdriver to loosen it. hopefully that solves the problem.
if you cant figure it out, ill go snap a pic for you