The "Poor Man's" method of determining whether your fuel/air mix is proper is to do a running plug test. This means:
1. Get a new set of plugs.
2. Put your plug wrench in your pocket.
3. Warm up the engine to operating temperature.
4. Kill the engine and install the new plugs.
5. Go for a ride down a quiet (low traffic) highway.
6. Ride for about 5 minutes or so.
7. Accelerate up to your normal cruising speed.
8. With the throttle open...hit the "kill" switch and pull in the clutch...leave the throttle open so air is still being pulled into the jugs even though there is no ignition.
9. Coast to the roadside. Pull the plugs. If the plugs are black and wet...your main jet is too rich...either go to a smaller jet or drop the needle a notch and try again. If the plug ceramic is glazed or white...you're too lean...either increase the jet size or raise the needle. If the plug ceramic is light to dark tan...you're probably "safe" and are not risking any chance of burning a piston or valve lip.
Some folks actually use a jeweler's loop to inspect the ceramic way-down inside. This is actually simple physics relative to combustion. The combustion chamber is an enclosed environment. If you flood it with gas (fuel) and no (or not enough) air...the spark fires but liquid fuel will not burn in this environment, i.e., rich condition and fouled plugs. If you put enough air but not enough fuel, the mixture will explode...white hot...enough to ultimately fry a piston head or burn the lip of the valve...lean. If you get just the right amount of fuel and air mixed together in an atomized state, bingo! We have a "happy motor"...