When I was 14 or so I found one of these at the neighborhood trash pickup, fixed a flat tire, put some gas in, and it ran:
(This one isn't mine, but I had two Solexes like that)
Note the forced air cooling - from the left side of the engine, air is blown towards the cylinder by fan blades around the magneto-alternator/generator. Also, note the carburator just behind the cylinder, above the gas tank at the right side of the engine. I remember once putting 5 cents of gasoline in it, which was 2 dollarcents at that time (around 1970). Usually it took up to two dimes of gasoline (50 Dutch cents). The exhaust was just a tiny pipe leading to a cute little round drum. It was a very economical 35 cc two-stroke engine.
Its default throttle setting was "full open", to reduce throttle you had to squeeze the little lever (see pic) at the right handlebar, and when you let go of the lever, off it went, purrrrr.
To start it, you had to bicycle forward, and then lower the engine onto the front wheel. Note the handle for the engine and its hook at the steering column. It did have a centrifugal clutch that enabled you to stop with the engine running.
Then, on my 16th birthday, I got a 'real' Puch moped like this one:
This was a 50cc two-stroke moped with forced air cooling, note the air conduit around the cylinder. It had two gears, and it ran 45-50 kmh whereas the Solexes only went around 25 kmh max.! The frame is just a few bent plates welded together.
The clutch, gear shifter, front & rear brakes, throttle - all controls were exactly in the same spot as today's motorcycles !
The Puch served me fine for about five years, until I got a cage (Citroen 2CV).