Hey everyone, I’m in the final stages of my ‘83 K100 restoration and finally fuelled her up and got her running. Problem. I noticed the speedo needle was occasionally flickering or bouncing, sometimes as high as 40 or 50 kph while at idle and in neutral. I popped her into gear and there was no speed registering on the gauge. Nadda. I removed the sensor and did the soldering iron test, and it was perfect, showing around 60kph as expected. The pick up is spotless and the FD oil is fresh. Any ideas where to go next? 
Thanks in advance

i also have a bike that does that ....

not sure of the fix just yet but it could be the power supply line to the meter movement being slightly dry joint 

im thinking on the backing ribon circuit between the input pins on the lunchbox connector and the actual speedo amplifier , then onto the motor .
on gerty i had duplicated the wiring with solid cables soldered to the connectors going to the pins to the electronic boards .
 which solved several issues including the meters dropping out occasionally ...requiring the bump the instruments fix ...till the next big pothole .
remember ... support the loom cable before it gets to the instruments connector .so that it doesnt pull on the pins in the lunchbox .as it hangs , wearing out the plating coating of the pins 


hope that helps 

I had an instrument panel where both the tacho and the speedo did that. Turned out to be the coil springs that return the needle to zero were displaced - a quick ping with a small screwdriver fixed that.

Thanks for the replies lads. I do have a spare instrument cluster, so wondering if I should rape it for parts. Maybe I’ll just swap it over to see if that fixes the problem. Only issue is that I want to maintain the odo reading on the original cluster as the mileage is verified

KiwiK100 wrote: Only issue is that I want to maintain the odo reading on the original cluster as the mileage is verified

Easy done. The very early versions of the instrument cluster actually dismantle completely, so it's easy to set the numbers where you want them. The later ones don't, but a thin jeweller's screwdriver inserted between the drums disenages the ratchet and enables you to rotate the drum. By 'the later ones' I'm still referring to the '83-'85 K100s that have the dual fuel level indicators on them, but it also applies to the '85-onwards single fuel indicator versions.

Thanks Dai, not sure about the integrity of the rest of the cluster however I’ll hook it up if only to see if the speedo works, and what other bits do or don’t. Know the GPI screen is toast. Both clusters have the dual fuel level indicators, so that’s a good start

I’ve swapped the instrument cluster for my spare unit and the speedo works fine, so where do I start… I took the back off, and the the screen, and when I went to carefully prise the needle off, it literally fell off. Squeezed it back on, put it all back together and presto, all working now. That’s a lucky break! 
Thanks to Dai and Charlie for your input.

Ah! Good catch! (Literally, I guess! )