Sorry, I've been away from the computer for two days. Congrats on the tranny change. As I told you, it is pretty straightforward. Now we need to find you the proper side cover. Did you end up using channel lock pliers like I described to loosen the freewheel sprocket? Also, what belt did you end up using?
Regarding the plug fouling, it does sound like a sticking float. It may also have to do with the larger carb on that bike. The Grande has a larger induction chamber in the crankshaft than the one on the Ciao. The crank will therefore deliver fuel more slowly to the combustion chamber, and needs slower air flow. This is why the Grande uses a SHA 12.12 and the Ciao uses a 12.10. By going to 13 mm carb, you increased the size of the venturi by 30 percent! The proma exhaust and malossi airbox also allow much freer air flow. What size jet is in that carb? I doubt it is the problem, but it is worth checking. It sounds more like a float or needle valve problem.
Zippy, is my reasoning sound here?