For anyone curious, the weight restriction (USA) for a legal ultralight aircraft is 250lbs dry (safety equipment like a ballistic recovery chute is exempt frm this) so any of the legal
ultralights you see weigh that or less.
Yet this doesn't mean yer limited to the flying lawnchair style like my ol' MX, the following (complete w/bouncy landing lol) is a Fisher 202 Koala ultralight made from spruce and dacron (newschool wood & fabric) and has just a 250cc single cyl
YouTube - fisher FP 202 koala ultralight
Now while not as small an engine as the china girl, still... it shows whats possible, I had some stick time in a friend's Koala and it was a fine flying machine. I did wish for more climb, but I'll admit I was a climb ratio fanatic as there was more than one treeline that would try and ambush me as I innocently chased the local geese, did strafing runs on oblivious cattle, and generally trying to annoy as many golfers as possible
The closest to the china girl engine capabilities I've been able to find so far while still limited to "normal" construction materials are some of the earliest ultralights, foot launched and sporting 10hp(ish) chainsaw motors, like the Easy Riser;
Easy Riser ultralight, ultralights, ultralight aircraft, light sport aircraft.
Very similar to the first powered ultralight offered for sale as a kit, the Icarus II. John Moody of Brandon, FL is widely recognized in the industry as the "father of ultralight". In a foot launched McCulloch 101 powered Icarus II hang glider on July 27, 1976 John was the first to demonstrate ultralight aviation at the annual EAA fly-in convention in Oshkosh, WI.
While functional and with acceptable flight characteristics, the restrictive laws at the time were later changed to allow for landing gear and larger engines (greater weight) as to increase the safety margin on these very
minimalistic machines. We've moved on to much safer designs - much respect to these pioneers for showing us whats possible!
The sport of foot launched powered hang gliding is alive and well BTW I just never got into weight-shift flying, here's a good place to start though;
Powered hang glider - Wikipedia, the free encyclopedia