When one piston is at Top Dead Center and the other is 180° opposite at Bottom Dead Center, the pop pop pop pop you hear from a Johnny Popper is NOT left firing POP and right firing POP 180° later, the POP the human ear can recognize is the COMBINATION/ADDITION of BOTH firings (a quick 180° apart) followed by the relatively longer 540° coast cycle before the ear detects another POP. You don't hear POP POP then ---- ---- ---- (540°).

I don't think Harleys ever had twin carbs. The reason they sound the way they do at idle is because of the way the crank shafts and firing order are set up.



And I would say that the "Popping Johnny" was a four stroke and "Popped" for the same reason a "hit and miss" engine does.

The "hit & miss" engine have a type of governor, mechanical weights that worked by centrifugal force against springs, once the engine reached the rpm to short out the magneto, stopping the spark, combined with a very heavy flywheel that kept the engine spinning,until the rpm was low enoughfor the centrifugal weights to retract by spring pressure, then would stop grounding the spark allowing the engine to start filling again untill it reached the cutout rpm.