Thanks captinjohn, I will give that a shot. Walbro lists several modules that are I believe as they phrase it are " warranty oriented". The reason this came about is a fellow flyer converted a 22 cc Poulan. It ran like a Rolex but even with a properly sized larger carb and a side dump muffler its top end seemed limited. This was verified by putting on succesively smaller props with no increase in rpm. The liminting modules alter timing to keep a set rpm max. they dont necessarily skip like a limiter on say sport bike, if they did it would be easier to tell when you had one. The Stil 4 cycle trimmer engine will do that skipping but it is the only one I have experirnced so far.