Sporking? That's whet you kids are calling it now?
You could try hooking a multi meter to it, set it to ohms so you got some current going to the thing. I'm guessing that it works like a magnet pick up, in that when there is continuity (or no continuity, depending on how it's made) that would be one revolution converted to tire size or distance traveled. (pull the plugs, put it in gear, roll it to take the slack out of the gear train and find continuity or no continuity depending on how it's made, mark the tire or hang some thing off the bike to get a distance measure at that point, roll it again till you get a continuity/no continuity, and measure the distance traveled. Plug that into your formula.
Or find a GPS and head out for the day.
Are you getting no indication at the speedo? Did the speedo come with a wiring diagram you can post?
It's eight and a half gallons of gas; and an engine. What more do you need?-- BMW R80G/S
Save lives. Legalize lane sharing.
Cow eyes don't glow.