Dear Bob
If it is an Isetta Burgman one would assume that the engine, gear box, and rear suspension will be from a Suzuki Burgman scooter in an Isetta chassis. If that is the case, there are two front wheels, one rear wheel, and this little side wheel, which makes 4 wheels (not 5 or have I missed one).
Do we know what the extra little wheel is for, and how and when it operates?
Chris Thomas