Do the floats have to be adjusted on mikuni carbs that came off of a 900ss before they can be used on a 750 Paso? Does anyone know a good way to check for proper float height or have a measurement to go by?

as far as I know, the float height on a carb sould stay the same no matter which bike it is on. the float height is specific to the carb, not the bike. when the carb is transfered from one bike to the next it is the jetting that needs to be adjusted. just try to look up the factory specs for your carb. flat spots at full throttle could implicate too small or to big of the main jet.
now I am not an expert by any measure, but I thought I'd throw my 2 cents in and hope it proves helpfull!

...............pikey