Most Maxi's were powered by the one-speed E50 engine, while the Magnum, and some Newports, and an occasional Cobra and certain Maxi's had the two-speed za50.
From my experiences and readings, the E50 is about as close to bullet-proof as you can get from a moped engine. There are very sluggish off the line, but run great after 10-15mph, on flat ground...but again leave much to be desired as for climbing hills. It has one centrifugal clutch, usually two-shoe (after-market and later years had three-shoes). The clutch shoes are adjustable, by turning in or out the set screw above the spring in each shoe.
The "2" classification on your Maxi, more than likely refers to the 2hp engine, which should have a 14mm carb and intake, and depending on which piston/cylinder, will have a 12-14mm round intake port, or a rectangle shaped intake port.
Hope this helps.