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kinda funny.
"A Harley engine has two pistons. The difference in the Harley engine is that the crankshaft has only one pin, and both pistons connect to it. This design, combined with the V arrangement of the cylinders, means that the pistons cannot fire at even intervals. Instead of one piston firing every 360 degrees, a Harley engine goes like this:
A piston fires.
The next piston fires at 315 degrees.
There is a 405-degree gap.
A piston fires.
The next piston fires at 315 degrees.
There is a 405-degree gap.
And the cycle continues.
At idle, you can hear the pop-pop sound followed by a pause. So the sound of a Harley is pop-pop...pop-pop...pop-pop. That is the unique sound of a Harley-Davidson motorcycle. It is described by aficionados as a "potato-potato-potato" sound.
"
http://auto.howstuffworks.com/harley3.htm