ok i had this problem take the front wheel off, the speedo , and the black speedo unit comes away from the wheel look into the black unit there is a dark brown magnetic coller about 30 mm deep it should have two brown lugs coming off it what happens the wheel has to metal pick ups that spin the coller round as it moves . on my bike they broke off i used liquid metal to build up the broken lugs it set hard put it back together it did start to work for about 20 miles plan A then broke off trying somthing harder now hope this helps
rattie
November 2009