How light can a nanolight trike get?
If we assume that you’ll be using one of the more common engines, like the ubiquitous SOLO 210, then you’re stuck with an engine weighing about 11kg (with untuned exhaust), a reduction drive (about 1-1/2 kilos), a prop (1-2kg) plus engine mounts (about 2kg), for a total of about 16kg before you even add a frame, seat and wheels. Experience seems to show that about 30kg (66lb) is about the minimum total for engine, prop, redrive, tank, frame and wheels that you can expect for a really simple, but strong machine, before parachute and fuel. A few kilos can be saved using a lightweight engine like the Radne Raket at the expense of climb rate and (because it tends to use a bigger prop), prop clearance.
