I've done this many times on my sons race quads. If you get tired of cutting plugs you can use a magnifying glass and a strong light to veiw the smoke ring. I use what a doctor uses when they look in your ear it has the light and magnification built in, my wife got me one from the office she worked at.
I'd say, if it was me, and I felt I ran it long enough wide open or on the main, I'd go up one jet size. Now, if you don't see any white or grey specks on the plug you could put a new one in and run it longer than you have this one and recheck it because it takes a while to get the smoke ring to develope fully. If you want to be on the safe side go up a jet and run it until you can see a solid ring with your eye and a light, then cut threads and look closer.
Depending on the fuel your using and the plug direction in the cylinder you may get different colors and partial rings.
