I believe the CDHPOWER offers the same engine on ebay as California Motorbikes,
called the super PK80. I like that CDH supplies a 36t sprocket, a heavy duty
chain, and free shipping, all for $145. It's a close call between the two:
CDHPOWER New cylinder 66cc/80cc 2stroke Engine Kit Motorized Bicycle-super PK80. · Bore x Stroke: 80cc:47mm x 40mm; Max. Power(kw/rpm): 80cc: 2.1/5000. Gasoline motor: silver 80cc, Engine Type: Single cylinder, air-cooled,2-stroke.
www.ebay.com