For the speedo, normally the little signal converter on the Speedo sensor goes bad. You would have to replace that. Most think the cost is not work the fix of the inaccurate speedometer. If you decide to pursue a fix, there is some threads here that will show how to test the gauge or the converter. Make sure of which component is bad before replacing. Make sure the little spin wheel is still intact and spins freely on rider plate rear left of nozzle.