Almost all of the step through vehicles which lend themselves to a low seat height and feet forward position are CVT. The Kymco People 200i might be a good starting point.
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KYMCO People GT 200i Overview - KYMCO USA
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Or the Honda SH150i. Both have 16 inch wheels. I hope to have a new Honda PCX150 to play with by next week but it is barely 13 hp and has 14 inch wheels. It is super efficient though but it would need a gearing change to make it to 80 mph which is very inconvenient to accomplish on a CVT.
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2013 PCX150 Overview - Honda Powersports
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The Honda Rebel has a low seat height and is available used but is still carbureted and air cooled.
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If Honda wanted to start from scratch with the frame and bodywork to copy Craig's drawing, they could fit a small bore and detuned version of the current CBR engine and break 130 mpg at 100 mph right off the show room floor for $5500.