So here I am drivin down the road..speedo is dead...yay, then every once in awhile when I would rev the engine for a downshift the speedo needle would hop..go up to correct speed only to fall back down again. Fixed itself after 2 miles and all seeme dok. Any quick things I should check or shoud I wait till it does all the way?
Mine did the same. Cleaned up the speedo sensor and it fixed the problem - for a few weeks and it was back again. Cleaned up the sensor and the speedo would not work at all! Decided it was not the sensor. [ .... .... .... ] <- making a long story short.
In one of the 12-wire Deutch connectors inside the headlite housing one of the wires [orange with white] was loose on one side of the connector. I have been unable to dismantle that type of connector so i jammed a piece of toothpick in there to tighten up the connection.
Not very happy with it but i have put on several hundred miles since with no problem.
Does the speedo light go off or stay on? if the light goes off [easieast to tell at night] then the problem is not the sensor.
Since the light stays on it is probably the sensor. The hard part is: i can see the sensor bolt. It uses an allen key socket. But it is at such an angle that i cannot get the socket into it.
I remove a oil hose bracket; helps a little but i lost the nut; have never found it. I think i removed the rear exhaust; then i was able to do it, getting very sore fingers in the process. I think it is easiest if you remove more stuff so you can actually get at it with a socket. Remove the rear brake master cyl and possibly the sprocket cover. I do not remember exactly off hand, but it is more than what appears at first. It is easier to get everything out of the way first than to fiddle with not enough space to work.
I also had this problem, intermittent speedo. The cure for me was to make sure that the engine light was 'out' BEFORE hitting the start button. It seems that every time I rushed the start sequence this problem occured. It only happens if I forget to let the 'Engine' light extinguish before pressing the start button. Apparently, the 1200S models don't like it when you interrupt the test sequence prior to starting the bike. I believe the '04 and '05 models have the same type of ignition/electronics test sequence but I am not absolutely sure it will cause the same problem as the 'S' models. Don't know if this helps you, but it worked for me.