I have a ‘91 16-valve K100 which has sat for several years and which I have not yet attempted to start up. This thread has two purposes:

1) to connect with K-bike respectors in Las Vegas area to meet up with when I’m down there. Troubleshooting help, go for a ride once it’s running.

2) to document plans and results of getting a bike going again after it has sat for an extended period. I’ll use this thread as a to do list, and hopefully it will help others.

Will post more soon…

Several years? Not good. 
Expect:
- drain all fluids
- change all the tank internals: filter, pump, pump rubber damper, pump filter, hoses, and carefull drain and clean the tank. 
- the front master cylinder will leak if it's not leaking yet. Dismantle and check if there's no corrosion inside the cylinder itself: if not, you can change only the piston and the gaskets. If there is, change the whole master cylinder, for aprox 400$...
Pay attention to the front central brake line: it's prone to crack. If there's any doubt: change.
- the crankshaft rear gasket will leak soon after a restart. You can wait for it, or change it before the oil contaminates the clutch.
- of course, a new battery is needed.

A standard restart service for a K needs around 1000$ of parts.

Thanks jbt, appreciate it.
So it’s a slightly more expensive transient delight, fair days ahead!

Definitely figure on needing to flush the brakes and take a hard look at the front brake master cylinder.  If the bike has been idle for more than two years I would look at getting a new fuel pump and vibration mount.  There are places that sell a kit with the pump and the mount for a reasonable price.  I think EuroMotoElectrics has one. 

Of course, you are doing a fluid change, oil, filter, splines, coolant and gear oil.  Fork oil would be nice, but not absolutely necessary.  I would wait to see what the air filter looked like before changing it. 

Keep your fingers crossed that the ABS isn't throwing a code.  Depending on miles, the rear main seal may possibly be good, but I would plan on changing the o-ring as soon as possible. 

I don't think you need to spend $1000 to get it running.  I would figure about $150 for the pump and vibration mount, a couple bucks for the clutch o-ring, and about a hundred for all the fluids and oil filter.   Check the date code on the tires.  There is a good chance they need to be replaced.

Thanks .75
Very helpful
I’ve ordered from EME before, looks like they have the kit with pump for $240 or so. Will look into your post more soon

Firstle: don’t know. Last sticker appears to be Dec 2013, so let’s say ten years.

did you try new fuel and cranking the bike over ? BMW K1 restart after 12 years standstill - YouTube

Firstle: thanks for the video, that was a good watch. If I was in a pinch I would put in fresh gas and give 'er a go. Hesitant to do that, however. If the rubber dampener has gone to mush, it may be quietly falling apart in there, ready to clog up the fuel system 50 miles into the desert. Not really into that so much. I have the luxury of making a bit of a plan here.

NOTES (I'll research/expand on this. Opinions welcome): 
[removed and updated below]

I would skip the Beemer Boneyard "kit".  If the bike has less than 50k miles I doubt you need the expensive air filter unless it was converted to a mouse condo.  You can get the oil and fuel filters at any auto parts store for under $20, just avoid Fram.  NAPA 8032 fuel filter and a Carquest 85348 oil filter.  If you get the Endurolast fuel pump kit, you can leave out the fuel filter..

A set of NGK plugs should only cost about 15 bucks.  I've had 5 bricks with mileage as high as 120K and never changed a crush washer and only one oil filter o-ring which I got locally for $2.50.  Get a jug of Castrol GTX 10W50 at Walmart for $25.

I use Peak Long Life coolant and mix it with distilled water from the grocery store.

I use Walmart Synthetic GL-5 gear lube.  

If you have the time or ambition to do the forks, almost any Automatic transmission fluid will work in them.  It has the added benefit of having additives that soften up the seals.

It shouldn't cost more than $100 to do all the Maintenance items less the air filter.

I have a 1983 K100RS that sat for 17 years at 29,000 miles. I have it 5 years and it's now at 58,000 miles. It's not my only K.

So my experience with it:

1: Replaced everything inside the gas tank [pump, filter basket, filter, mount, damper, pipes].
2: Replaced all outside tank fuel lines.
3: Replaced all vacuum caps, vacuum pipes, Z pipe [crank case vent].
4: Replaced all brake pads, brake lines, both master cylinders complete and caliper seal kits,
5: Full fluids filter changes.
6: Replaced clutch cable.
7: Replaced gas tank, it had corroded from inside.
8: Sundry items: indicator relay, temperature sensor, fuel pressure regulator.
9: Tyres [Bridgestone Battlax BT46].
10: Wheels needed to be painted but I got a pair of used black wheels and fitted those instead.
11: Rear shock, I took a YSS one off my RT and swapped them.
12: Injectors [I had good spares].
13: HT leads

Although warned about rear main seal its still there, I have the full kit in my shed for the day it gives up. At this mileage I will do clutch and all the other seals.

I have travelled lots with this bike, its been to Spain France England and I love it.

I knew when I got it that I was facing this list so there were no real surprises. The price reflected it and with these jobs done it has been reliable.

Thanks again .75
Notes are updated below

Thanks Olaf, that is a good reassurance. At present I am concerned with getting the engine running, and being able to ride safely. Once that has been addressed, I'll move on to the bike at large and will reference your list. 

NOTES (I'll research/expand on this. Opinions welcome):

Maintenance notes: If the bike has less than 50k miles I doubt you need the expensive air filter unless it was converted to a mouse condo. You can get the oil and fuel filters at any auto parts store for under $20, just avoid Fram. NAPA 8032 fuel filter and a Carquest 85348 oil filter.  If you get the Endurolast fuel pump kit, you can leave out the fuel filter..
It shouldn't cost more than $100 to do all the Maintenance items less the air filter.

Complete In-Tank Fuel System Replacement - Including All the Fuel System Parts required Inside your Tank
52mm Fuel Pump Kit - BMW K1, K75, K100, K1100 (to 01/93); 16 12 1 461 576 / EnDuraLast
Part #: FPK-576EDL
https://www.euromotoelectrics.com/product-p/fpk-576edl.htm
(Will also replace all fuel lines, with proper FI clamps)

Spark plugs
A set of NGK plugs should only cost about 15 bucks. (use NGK DCPR7E)

Oil change
Jug of Castrol GTX 10W50 at Walmart for $25. Filter: Carquest 85348

Coolant change
Peak Long Life coolant and mix it with distilled water from the grocery store

Gear Oil change
Walmart Synthetic GL-5 gear lube

Spline maintenance
I'm sure there's a good post covering this job somewhere...will look
This stuff may be good?
Enduralast 477 Spline Lube, 15 Grams
spline lube for use on all transmission, driveshaft, clutch and final drive splines on BMW motorcycles.
https://www.beemerboneyard.com/endura477splb.html

Brakes
- Definitely figure on needing to flush the brakes and take a hard look at the front brake master cylinder. 
- Keep your fingers crossed that the ABS isn't throwing a code.
- The front master cylinder will leak if it's not leaking yet. Dismantle and check if there's no corrosion inside the cylinder itself: if not, you can change only the piston and the gaskets. If there is, change the whole master cylinder, for aprox 400$...
- Pay attention to the front central brake line: it's prone to crack. If there's any doubt: change.
Master cylinder reading:
https://www.motobrick.com/index.php?topic=343.0
https://www.k100-forum.com/t18611-front-master-cylinder-leak
https://www.k100-forum.com/t2516-front-master-cylinder-fluid-leak

Rear Main Seal
- Depending on miles, the rear main seal may possibly be good, but I would plan on changing the (clutch) o-ring as soon as possible. 
Reading: 
https://www.k100-forum.com/t9812-replacing-k100-rear-main-seal
https://www.k100-forum.com/t15405-k100-rs-clutch-housing-removal

Tires
Definitely going to be changed
I was originally leaning towards Bridgestone Battlax A41, however
I'm sure I'll end up getting into some desert riding, coarse sand, loose gravel
I know it is not the K100's forte, but I also know this will end up happening... Battlax's aren't going to work so well
I have Shinko 705s on the '85, and I'm happy with them... but I'd rather try a different tire, gather empirical data

Battery
Replace. Will probably get a lightweight unit, small as will be reliable.

Fork Oil
- Fork oil would be nice, but not absolutely necessary.
- If you have the time or ambition to do the forks, almost any Automatic transmission fluid will work in them.  It has the added benefit of having additives that soften up the seals.

Some more reading:
https://www.k100-forum.com/t15884-k100rs-16v-putting-it-back-on-the-road

k100ing wrote:Tires
I'm sure I'll end up getting into some desert riding, coarse sand, loose gravel

At least half my riding is on irregularly-maintained gravel roads throughout Vermont. I use the Continental TKC70—110/80 on the front, 130/80 on the rear. The TKC70 provides an extra measure of traction on freshly graded gravel/stone surfaces, and loose gravel on the corners; road tires will wear out faster on those surfaces. The 70 also has good traction on wet pavement and isn't too noisy at high speed, but if you focus, you'll hear them howling like distant coyotes. 

The 70 also comes in the Rock model which is noisier on pavement and more for off pavement; however, a K100 has navigation limits regardless of tire choice that I'm sure you'll discover. I doubt you'll take your K100 through deep sand, gravel, mud, or moonscapes of potholes very often after you've done those excursions once but when you do one, please report back here with photos. 

I really should have an F650 or a DR650 but the K75 is so good at speed on the highway, I'm sticking with it—primitive Jetronic, good fuel economy, and all.  Multiple motos aren't in my program.

Just so you know, over here at least, you will get the following items that are common to Hondas in a Honda dealer at much better prices than BMW dealer.

Fuel lines
Oil filter.
Oils.
Coolants
Spark plugs [also NGK DR7EA or DR8EA will work too but for those you need the bobbins]
Final drive grease/lubricant
Tyres.
Exhaust studs.

Another item I did not mention but it will die, the pipe from the radiator cap to the coolant expansion.......cheap so do it straight off.

92KK 84WW Olaf wrote:Just so you know, over here at least, you will get the following items that are common to Hondas in a Honda dealer at much better prices than BMW dealer.

Fuel lines
Oil filter.
Oils.
Coolants
Spark plugs [also NGK DR7EA or DR8EA will work too but for those you need the bobbins]
Final drive grease/lubricant
Tyres.
Exhaust studs.

Another item I did not mention but it will die, the pipe from the radiator cap to the coolant expansion.......cheap so do it straight off.

Over here, no one beats Walmart or the big auto parts chains.  You need to buy a new bike every couple years to get a break at most dealer parts counters.