I bought a 1983 K100RS in 2018 with 29,000 miles. It spent 17 years stood in a nice heated boat shed. I have since brought it to 56,200 miles.
All good.
But you will face the same issues. I have been in Ks for a while so I knew what to expect and as the saying goes, it did not disappoint. The purchase price was right and I had a budget.
So I am happy to share the list:
First do NOT try starting them. You will bugger up your fuel system.
Fuel System:Check the gas tank. If it had old gas left in it, you need to clean it out. Budget for replacing fuel pump, vibration damper, holder, filter, fuel lines inside the tank. IIn the short term you might get by keeping the pump and repalcing everything else.
Outside fuel tank:Replace the outside tank fuel lines. Honda ones are the same 8/13mm.
Injectors:These are likely to need cleaning but if you do all the other stuff first you reduce risk of problems.
Electrical:Check and clean connections, especially the ignition system. Earths in particular. Also the big plug connection into the unit under the seatFuel injection control unit [FICU] and the igntion control unit under the front of the tank [ICU]
Check all the fuses.
Check if you have neutral light. If you dont, clutch lever has a switch that will allow the bike to start, just pull the clutch.
At this point you might consider trying to fire it up.
Vacuum:Replace the vacuum pipe from the throttle body cylinder 4 back to the fuel pressure regulator. The throttle bodies have vacuum caps, should be replaced. If any of the bikes have 2 fuel lights on the clocks, you will find a vacuum pipe on no 1 cylinder. Just put a cap on instead.
Crankcase vent referred to a Z pipe will be cracked, replace it.
Brakes:These are going to need serious work.
Replace brake lines.
Probably need rebuild kits for calipers and master cylinders.
Brake pads most likely toast.
Cooling system:Fan is a weak point, check it is not seized or stiff.
Pipe from radiator to expansion tank is likely to fail so replace it.
Cooling system hoses generally seem to survive.
Check under the water pump for coolant or oil leaks.
Obviously fluid and coolant change is required.
Check your air box in case mice have been in it.
Tyres will be well out of date.
I had to do all that stuff on mine, but I had a lot of parts and it was a diy job.
Given the low miles things like brake discs should be ok and engines mechanically should be spot on.
A known K fault is sprag clutch [starter clutch] spinning and not engaging. Oil change for a good clenaing oil will help this.
I know my RS when I add what I paid for it to what I added since, I would be about covered.
Check out where to go for parts, I buy most on line but places like
www.kpartsholland.com will ship to you. There is a great range of generic, oem and non oem parts out there. As an example the fuel pump in a K was used in most European cars of the same ra, VW, Fiat, Lancia. Citroen, Peugeot and more. I pay about €45 for them. You can get a full set of injectors EV14 from kpartsholland. I think about €150 and they come with O rings.
Dont be afraid to ask questions or for parts. Most of us have lots of spare parts that we swap or sell on.
When you get a chance, pull out their VIN numbers and put them in your signature. There are significant changes and upgrades and this helps others put you in the right direction.