[rotorwrench]

The chugg description will need further clarification. At what rpm is this chug and is it when the engine is under load or no? Engines will miss and rpm fluctuations can happen under certain conditions but the only thing that chugs is a steam engine in my way of thinking. Stuck valves can cause after fire in the exhaust and a lean fuel mixture can cause backfire through the carburetor. These would be like the definition of "chug" when related to motor vehicles.