I have a Techumseh HM100 159232K on a coleman 6250 generator, the problem is that the engine surges all of the time and will not level out, have replaced the carb, fuel lines , fuel filter, coil and tried resetting the governor. Starts fine, runs a short period of time and starts surging, seems to backfire in the exhaust after it runs for a short period of time. I have had several carbs on this engine andit does the same thing with all of them. Currently have a new style non adjustable carb on it.