Many times the cause of K bike speedometer flakiness is poor connections inside of the instrument cluster. This is especially true for 88 and earlier model years. Here's how to correct the problem:

1) Remove the instrument cluster from the bike. Exact mounting varies by model but all of them have four 5mm Allen bolts in recessed holes in the back of the instrument cluster. (Info on how to remove the instrument cluster from various different models can be found here.)The wiring harness connector is secured to the back of the instrument cluster either by a Phillips screw or 3mm Allen bolt.

2) Place the instrument cluster face down on a towel on a table. Remove the nine (seven on 85 and earlier K100s) Phillips screws from the perimeter of the back of the instrument cluster to remove the instrument cluster's back plate.

3) Once the back plate is removed you will see a three terminal connector on the top middle of the back of the speedometer. It has three long pins on it. That's usually the culprit. Pull it straight up. A small screwdriver can be useful to pry it out.

The picture below shows the inside back of a later cluster that had small screws to hold the connector in but this is the general location of the three pin connector.

4) Clean corrosion of of those pins with some steel wool, fine sand paper, whatever. Then, before reinserting it into the back of the speedometer, twist each of the pins slightly. That will help to ensure that they maintain good contact when they are reinserted.

5) Put everything back together and go for a test ride to see if that fixed the problem.

© 2013 Drake Smith - Please do not use or reproduce this elsewhere.  Feel free to link to it though.