Hi Team, just wondering if one of you has seen this before (I haven't). I was looking at a bike to buy (YES!! '85 K100) and as soon as the contact is switched on the speedo goes to full scale without the bike running. I wonder if the problem would be in the speedo or in the loom. Any thoughts/experience? Thanks!

Congrats with a "new" bike!

Remember similar issues from other forums.......then it have been a ground problem......don't remember if it was at the multiconnector or inside the instrument.

If its the yellow K either RT or LT 4,000rpm will give you 100kmh or 60mph and you can do the math from that.......

Thanks both. Re last, the bike isn't moving whilst showing full scale :-) So it isn't a problem of the adjustment. Thing is if it is the speedo I'm OK with that. Having to chase a fault in the loom is something else..

I had the same problem with speedo fluctuating when stationary when the battery was below 11 volts. A couple of days on a slow charger made the problem go away.

Did you end up finding the issue?

i think inge is on the money rene ...

the typical issues with electronic drivers are that without a good reference (earths and supply voltages ) ...the electrical offset can be quite wild in outcomes

have seen some early tackos do similar with overshoot and lag   strangely the later series after 86 perform really well n such things

i suspect a circuit or parts - component change solved these issues

deoxit mate ...and test the connections

good luck !

Cheers team, finally brought the bike home today after all kinds of shenanigans with registration etc.
First time the opportunity to have a proper ride (from seller to home - about 40 miles), after a quick up and down the street during purchase discussions. Bike steered like a pig at that time and was wondering about the head bearings, forks etc. Today brought a compressor and found front and rear tyres with little air..... So she got some fresh air in her :-)
At the time we wanted to get the bike home, now two weeks ago, I brought a container with super unleaded with techron, as the owner kept the tank very empty. Filled her up and started easy. Fuel looked good (clear) before I put my lot in. Added a bit extra techron and blipped the starter a few times to 'flush' and then started her in honest. All good, no problem. Fitted a spare tacho and it worked good, no full scale anymore, so the original tacho needs some work.....
This morning, after getting the tyres on pressure, decided to bring here home. Barely around the corner she started lurchin and a 100 yards later she quit on me. Lights OK, bright enough, but a few times not turning over/not running the starter. Had brought some tools and quickly determined that the battery was OK, fuses OK, pump could be heard running when you blipped the starter..... Hmmm, meantime 100F outside and inside the helmet serious boiling point was reached! Looked in the tank and found some sort of milky liquid. WTF?! Where did all my fresh expensive fuel go? With the cleaner? Of course I stood there without container and no fuel pump in sight......
Called the seller, explained the situation, told him I needed to get a hose, drain the tank and get some fresh fuel in her. He was good and showed up a bit later with two containers and a hose. We drained the tank as much as possible and filled her up with the fresh fuel. Bike started readily (thank god!) And I was ready to continue the 39.9 Miles.
As My previous bike was a RT and before that a Honda with fairing I had completely forgotten how much wind pressure you get on an unfaired bike. With the temperatures here in Florida not completely unwelcome ;-)
Bike did well, had her up to 80 and she was steady. Rattling muffler shield of course and initially a bit hesitant on the throttle, but the closer to home the better it got. Have her home now. Noted that when using the indicators sometimes they both got on, blinking out of sync. Also the gear indicator went blank, not allowing to start without the clutch pulled, no all the usual issues displayed :-) With the starter issues etc a deep dive in the electronics is required, lots of cleaning to do. Luckily Deoxit on hand and lots of other sh!t.
Anyway, happy to have a bike again!

woohoo .!!

have fun with the fix up rene