recently bought an 02 MC 800 with A big bore kit, the guy I bought it from was not sure what size, is there a way for me to find out without opening it up. and should I just up One jet size from what it calls for ?
Unless you have some kind of gauge you can put through the spark plug hole to measure the bore, you just about have to take a head off to measure. It is not that big a chore. The most common big bores will be 925, not sure what bore that is, 990 is 91 mm, and 1010 I think is 92 mm.
If it isn't already jetted for the big bore I would go more like 4 sizes over the chart and then work back down if that is too rich.