Nearly finished my K project, updating a '85 RS, was going well but had done 150,000kms, with the running gear from a low milage '88 RS that I bought written off, with only 26000 kms on it.
The old motor/box and diff came out easy, the new motor/box and diff in easy enough. went to start wiring it up, opps the engine loom where it connects to the main loom is different, and has a different number of wires. To the wiring diagrams to sort out which wire was the extra one. Turns out to be the vacuum switch which was deleted in late '85, no worries, leave that one off. Now for the different connectors, well I did not want to cut either loom, in case I want to ever pit the original motor back in at some stage.
Luckily I also have an old '85 loom and an old '88 loom in the shed, so I cut the required plugs off those looms and made a short connector lead to join the later engine loom to the early main loom.
Later I found that the gear indicator loom plug is also different, so out with the soldering iron again and make another short converter lead.
I also fitted the later model foot peg plates, with the later micro switch type brake light switch, that part was all straight forward, but of course that entailed having to fit the later model exhaust system to line up the mounts on the foot peg bracket.
Another days work should have it up and running again. Hopefully the new motor is ok, I have never heard it running, it has been sitting in a basement 10 years. I am hoping that I do not have to do the water pump in it, but I won't know till I fire it up if the seal is still ok.

I am a happy chappy, filled the gearbox and diff with oil, filled the radiator with coolant and tried starting it this morning. It did not want to start at first, then fired up on only 2 cylinders. Checked spark on the 2 non running cylinders, seemed fine, cleaned the plugs and back in. Tried again, this time it ran on 3. Took the offending cylinders plug out again, put one in from the old motor, still the same. Left it idling away on 3 and tapped the fuel rail close to the non running cylinder and all of a sudden it burst into life on all 4. It must have been a minor blockage in the injector, I will run injector cleaner thru it at the first opportunity. The motor is as quiet as a mouse, runs like a Swiss watch, or should I say a West German watch.
Now back to the shed and put all the body work back on.

Sounds like you are a glutton for punishment and also sounds like you have BTDT but the good news is she is running so look forward to the ride report.

Well done Robin, great job!
Regards,
K-BIKE

Just been out looking at the bike, got to thinking, what is left of the original tidy K100RS I bought 2 years ago, after the 2 rebuilds I have done on it it the last 6 months? The first one after a car tee boned me and wrote the bike off, and the last one to update it mechanically.The more I looked and thought, I realized the only original parts left now are the frame, wiring loom, tank, side covers, 1 Z bracket,one lower fairing,the radiator and surround, one mirror, the handlebars and the switch gear. So my next question, is it the same bike?
Parts I have replaced are front wheel, front forks (from a limited edition) front guard, fairing upper, 1 fairing side panel,complete instrument panel,(twice, I keep finding better ones) complete motor/gearbox and diff unit,rear wheel, seat, tail section, seat lower panel,fuel pump, 1x mirror and probably more that I can not recall at the present.
I have totally enjoyed the rebuilds, now look forward to putting a few miles on the old girl.

Revvvvvvvvvvvvvvv her up and head for the hills

And watch out for the dick head relatives of the last swine who ran into you.
Regards,
K-BIKE