Just got my 1991 K100rs last week.  It ran rough due to a cracked throttle body boot and a bad fuel injector o ring. Fixed boot and it run good but not perfect.  Its super clean but has some miles 60,000.  Has a Ohlin shock which was icing on the cake. Im happy with the 2500$ purchase price.

Welcome to the forum Vannatta Looks like you got yourself a bargain there.

Problems I found so far.
Vibes kinda bad at certain RPMS.
pulls to the right a decent amount when i let go off the bars at speed.
Bad intake rubber boot. temp fixed with rtv until new ones arrive. MASSIVE VACUUM LEAK.
Fuel injector sucking in air.  Replaced all orings on the injectors.
Vacuum line from fuel pressure reg leaking fuel.  FPR ordered just need time to install. 50$ from amazon..
Handle bars too far for my reach.  Risers installed. Big help there
Temp gauge not working.  faulty sensor in water pump.  Dont know where to get one yet...
throttle cramps the palm of my hand BAD very quick.  Risers help its just a heavy throttle i guess.
Rear turn signal out.  New bulb installed
Fuel tank over flow always leaking a bit of fuel.  Should I cap it off??
rear brake just started squealing bad.  new pads i guess. part#?

Runs much better but smells rich.. I hope the fuel pressure reg fixes that but i doubt it will.

Need to.
Change coolant, tranny diff, and rear drive.
Replace any rubber hoses when i have it apart to change the rubber intake boots.

So far even though i have all these small problems i love the bike:)

Once the engine is running as it should the vives will just about dissapear. I have a K1100 and right on 4000 it tingles but keeping it well tuned does help. I am putting a 2.61 ratio drive in to get better fuel economy and get the revs lower so the vives aren't right on the speed I sit on.
The temp sensor,  try EME but they only list the ECU sensor.
As regards the heavy throttle check to see if the grip is binding on the housing its a common problem and of course the cable could be getting old and the teflon liner is cactus.
I know what you mean about the low bars, I love the RS models but cant ride them because of hand problems and one of the guys here is having carpal tunnel surgery very soon because riding was near impossible for him.
Some of the guys here have used the bars from a K75c which make things a bit better.
Pulling to the right, check the wheel alignment we have seen a bent and twisted swingarm here a while ago and tire wear can do it also worth checking the frame for true, they are a very strong frame but all the same can bend.
Check out this site it gives a wealth of info for the new owner http://www.verrill.com/moto/newkbike.shtml

I just read the temp sensor might need to be removed and cleaned. Corrosion will stop it from getting a ground. I checked the throttle and the resistance is in the throttle bodies and maybe the cable.
The tires are old and I should replace. Hopefully that will help. Thanks for the great reply

yep new tires ..makes a huge difference to just about all bikes we have on the forum

the old tyre compounds  have been revised in recent years ...all with positive results from the major brands

i replaced the FPR and went ahead and replaced the leaking intake rubbers.  I just went to the part store and used radiator hose cut to size to replace those pieces since the ones I ordered are going to take a long to time to get here.  It idles higher now and the vibes are hardly there.  The FPR solved the running rich issue.  Im happy!

Another win for the K Team!

Welcome Vannatta! 
It looks like the New Mexico sun has dried out the rubber bits. Also check the condition of the vacuum plugs on the throttle bodies as well as the "Z" shaped hose that leads from the crankcase to the air box. Vacuum leaks do find their way to the handle bars. 

When you say fuel tank overflow I assume you are referring to the drain lines. One of those allows water to drain from around the fill cap and the other is a vent. If you are leaking fuel from either of these I would say the fuel lines inside the tank need attention as well. 

You may just be best replacing all of the fuel lines as well as vacuum lines. The ethanol in the fuel really contributes to the degradation of the rubber.

The issue with the throttle may be the result of the friction screw that is located on the bottom side of the brake lever perch. It is a "poor man's cruise control". It has a knurled head about 3/4" in diameter. Try to back that off and see if the throttle frees up some.

The z bend hose is bad but I don't know where I can get a replacement? It seemed to stop leaking fuel after the fpr replacement so that's good at least now. I checked the throttle with the cable unhooked and its smooth as butter. Seems its just the throttle body return spring are just strong.

You can get the crankcase breather hose at most dealers or beemerboneyard

http://www.beemerboneyard.com/11151460480.html

Beemerboneyard is a good resource for parts. Fortunately these bikes are still very popular and dealerships still stock parts for them. Check out realoem.com to find part numbers and then copy and paste into Google to comparison shop.

Vannatta20 wrote:The z bend hose is bad but I don't know where I can get a replacement? It seemed to stop leaking fuel after the fpr replacement so that's good at least now. I checked the throttle with the cable unhooked and its smooth as butter. Seems its just the throttle body return spring are just strong.

had the same issue with a clutch cable ....unloaded was as smooth as ...but with even just a little loading was tight and grabby

lubricated it with lanotech (lanolin based lubricant ) and a cable lube adaptor  till I could buy a new one
good luck

Hi Venatta,
Good to have you with us, post your questions over in the technical section, not all of the gurus read the new member introduction section so they may miss your question.
Regards,
K-BIKE

Vannatta20 wrote:Its super clean but has some miles 60,000.

welcome to the beautiful world of the K100.

60,000mi,.... The bike is just ready for serious riding.

CF

Sounds like the bike is coming together nicely Vanatta, welcome to the Forum.

88KE

Planning on going on a month long rode trip start at the end of the month. Can't wait!