Originally Posted by
Tony Hallo
Can you describe pulsating when on the lean side? I'm guessing the engine is lean and slows with constant throttle setting, as engine slows, fuel requirement decreases and at constant throttle setting the mixture become more rich?
You are spot on, that is exactly what happens. In model engines it is a very light RPM oscillation, barely audible, with a repetition frequency of somewhere between 0,5 and 1,5 Hz.
In vehicles, ti is a bit slower (typically less than 0,5 Hz) and more "feelable" than audible or visible on the gauges. You don't really see RPM or speed oscillate, you don't really hear it, but you feel a distinct light "tugging" on the seat of the pants so to say.
Over here in Europe it is a very common thing with ethanolated gasoline in carburated cars and bikes... There are certain fuel additives that cure the issue up to 10% of ethanol, but rejetting the carb will also cure it.