RE: What motor is this
hpelsromantic,
Put a pop cicle stick all of the way into the exhust port. Carefully center it. Turn the crak and make an impression in the stick. Measure the distance from the mark to the end of the stick. 44mm=3.2,45mm=3.1,48mm=4.2,49mm=4.1. A smaller bore is a 2.4 or less. The carb ventri should be no 15mm=4.2 or 4.1,13.49mm=3.2 or 3.1. If you post the cylinder model that is cast into the cylinder mounting flange, the guys here could tell what it is exactly.
Dave