I've also posted this elsewhere, so my apologies if you've already seen it...

I have a 2002 RC51 that I purchased about a month and a half back. Recently, after adjusting the chain, I noticed that at times my speedometer would start acting erratically. For example, if I take off from a light normally, the speedo would read normal, and as i shifter up it would start bouncing around from say 40 to 34, then to 36, to 23 and so on. At times it will just go to 0 and stay there for minutes at a time.

The bike uses a hall effect sensor which I have read to be the same sensor used on the CBR600F3. On my bike it bolts in to the back of the crank case, runs up the right side seat frame and then into the computer. I originally made sure the original one was plugged in tight and I have since put in a replacement, to no avail.

I'm really trying to figure out what to look or check for next, as the sensor plugs in to the computer harness, then from there the computer wiring goes in to the dash panel. All other functions read properly on the dash panel. (temp, mileage - when the speedo is working, RPM, and trip distance as well as all the lights like fuel level, turn signals, neutral, etc)

FWIW I have thought that maybe some tight links in the chain are causing the sensor to get readings that jump around, confusing the computer, leading to the numbers jumping, and or reading 0. I'm ordering a chain to install to test the theory, but I'm not sure it will solve anything other than replacing a chain with tight links.