I recently bought a ASPT (assembled from parts) bike which has a Softail style frame with HD running gear (1340 engine). My problem is that it has Big Dog fuel tanks with a 2000 ProSport speedo which seems to run 10 mph higher than what my speed actually is. Is there a procedure to calibrate the speedo so that I'm closer to true bike speed? Using the mileage that the speedo provides between fill-ups comes up with about 62 mpg which I know just can't be true! Any help would be greatly appreciated. Thanks