I have a mid year 1985 K100RT.
I read that late in 1985 BMW removed the Vacuum switch and the TPS.

Can I do the same to mine?

Anyone know why BMW removed them?

I read it on line at another forum but I understand that it is factual.
I don't have the actual link.

I just want to see if anyone else knows of the issue and resolution.

Yes, on reading again it does not say that the Idle switch was removed just the vacuum switch.

I guess the easiest thing to do is to just remove the hose that goes to the vacuum switch and plug up the ends of the tube and the port. Then essentially the switch is out of the circuit.

I'll give that a go.

Why would you remove it?

For adventure, Marshall. I'm now inspired to start removing engine components from my bike to alleviate ennui.

I just have a feeling that BMW wouldn't remove the vacuum switch unless there was some advantage to doing so.
THE EFI and fuel injection system is already complicated and I wondered if they thought this was a way to simplify it.

That could be.

I read your past posts about your engine stumbling at take-off, especially after long cruising stretches. Did you ever follow the advice about looking for air leaks, checking valve clearances and performing a throttle body balance, Gerry? If you haven't yet, now may be the time. It would be helpful if you put the outcome in that other thread for owners who may have a similar condition with their bikes.

It's also helpful to readers if you put the year and model of your bike in your profile so it will show up in each of your posts. Adding your general location is useful because willing helpers may live nearby, as far-fetched as that may seem.

You haven't checked valve clearances then balanced the throttle bodies?

According to notes on a schematic from Bert in 2009, the vacuum switch was used to adjust ignition timing at mid-throttle, but was removed by late 85.  It connects to pin 15 of the ignition control unit and opens/closes the circuit to ground. 

i can't imagine that signal would matter much in normal riding, except a cracked hose would be an unmeasured air leak and it would cause the idle to be low due to a leaner mixture.  The same would be true for the vacuum line to the fuel pressure regulator that is not visible without removing the air filter housing.

You said you changed all the visible vacuum lines--so i figured you didn't change the line to the fuel pressure regulator (FPR).  i'd bet that your line is cracked in the sharp bend where it exits under the regulator.  The line originates at the rearmost throttle body port and is covered with a coil spring wire, all the other throttles should have a rubber plug covering the port.

FPR operation:
The FPR maintains a constant difference between the fuel rail pressure and the intake manifold pressure just below the throttle butterfly valves.  This constant is the regulator set point which is 2.5 bar or 36 psig.  Internally the FPR has a spring-loaded safety valve to provide fail-safe operation in the event that the feed line is cracked and leaking, and the safety release pressure is 4.7 bar or 68 psig.  In addition the fuel pump has an internal relief valve at around 70 psig. 

This design ensures that fuel is always flowing in the rail at a pressure about 36 psi greater than the pressure in the vacuum tube line whether it is intact or leaking.

Another possibility is water or sludgy ethanol in the bottom of your tank.  Catch a slug of that and the bike will stumble for a few seconds.

It's fairly easy to drain the tank if you lift it up and back slightly to expose the front left fitting (return line), loosen the clamp and pry the hose off the tube and push it down and out the side into a catch jug of sufficient size.  Then remove fuse 4 and 6, and use a wire jumper from the right side of fuse 4 to the left side of fuse 6 to run the fuel pump and empty the tank.

Examine the contents at the bottom of the catch jug.  If it contains water with dirt, black floaters and jelly then that may be your culprit.  Remove the gas gap cover to examine inside the tank.  Clean, rinse and repeat as necessary.  Don't re-use all the old fuel--you don't want the junk at the bottom to get back in there.