ORIGINAL: TimC
A little more info on the Sportster series JollyPopper. There is no sleeve in the cylinder. If you score the cylinder somehow, it's throw away time. Being a loop scavenged engine, an idle bar plug seems to work best.
And like CCRC1 said, lots of castor for this plain bearing engine.
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All of my Sportster engines are schneurle ported. Not a baffle on a piston anywhere. <G>