Anyone help please,
There is a small (6mm od) rubber pipe that comes off No1 Throttle body where does the other end go to I can't see even with the tank off. It looks past it's best where is attaches to the throttle body. Many thanks

Should have said K100RT 1886.

eastern_phoenix wrote:Should have said K100RT 1886.

That`s a really old model, you must search info elsewhere.

eastern_phoenix wrote:Anyone help please,
There is a small (6mm od) rubber pipe that comes off No1 Throttle body where does the other end go to I can't see even with the tank off. It looks past it's best where is attaches to the throttle body. Many thanks

Early models did have a vacum switch connected to TB #1, I think the switch was removed 04/85.

From what i have read on different forums, it can be disconnected w/o any problems.

Should have said K100RT 1886.

Isn't that the coal and steam version? ''

Dont let these guys take the mickey out of you e-p,
you just sent them looking in the back of the bookcase for text written in ink and quill. silly

eastern_phoenix wrote:Anyone help please,
There is a small (6mm od) rubber pipe that comes off No1 Throttle body where does the other end go to I can't see even with the tank off. It looks past it's best where is attaches to the throttle body. Many thanks

If by "No 1" TB you mean the TB closest to the front of the motor then see Inge's eggsellent 'splanation...but if you mean the back most TB then the vacuum hose goes to the fuel pressure regulator right behind the TB set. Plug off the other three TB vacuum stubs with rubber caps available at any auto parts shop.

Thanks Inge I had seen this diagramme in Clymers manual I think but it is not very clear as the hose comes of a tapping beside the closed off vacumn Guage (used for synchronising) and bends to the front and disappears behind the air box.
I have read Bertrand Vogels (Crazy Frog) excellent write up on the EFI and I see that the vacumn switch is normally open and when closed by the Vacumn it earths pin 15 of the Electronic ignition module but what for I can see no explanation as to what this does.
My recently aquired K100 had a few problems which I have irones out but on starting it miss fires (not badly) unless I keep the revs up until it warms up. Once warm it ticks over Ok (950 rpm) with an occaisional miss, It goes well and is giving 45 MPG when pushed hard 30 miles of 70 Mph + so there not a lot wrong but this small hose looks a bit grotty and suspect. So do I pull it off and plug it or replace the bit I can see (it is only against the TB that is a bit suspect) and cut it short and put a new piece in with a paralell conector.
Any advise welcome thanks

Oh I forgot to say that the bike will pick up in any gear from 1500 RPM.
Thanks

I should have said that the bike picks up smoothly from 1500 Rpm in any gear,

Have no experience with this vacum switch myself, but from what I have read on other forums...owners have disconnected the hose and not noticed any difference.

I suggest you do the same, and put a rubber cap at the stub....and it could be that it improves the engine cold running,,,if the tatty hose have a small leak.
But this could be tried first, and then we take it from there....

If I remember correctly the switch would advance the timing a few degrees to improve fuel economy, but it probably did close to nothing....since it was discarded after a short time.

Here is a picture of the switch (so you see where the hose ends):

+1 Inge

I had a bit of a rake-round on the net and as nearly as I can see that switch provides a bit more timing advance on a trailing throttle. Stops the exhaust banging and popping maybe?

On overrun the fuel is shut off anyway.

Small zip-tie on loose hose connections might help.

Best of luck

Thanks what you say makes sense i'll give it a whirl.

The switch in question activated a different advance curve for part throttle. It was effectly useless and discontinued. BMW runs surprisingly aggressive timing on their bikes. It is an area to which they devote more attention than is typical of motorcycle manufacturers.

You can put a TB plug over the spigot, remove the switch from the back of the TB rack, tape over the ends of the wires and secure them somewhere out of the way.

Themason wrote:The switch in question activated a different advance curve for part throttle. It was effectly useless and discontinued. BMW runs surprisingly aggressive timing on their bikes. It is an area to which they devote more attention than is typical of motorcycle manufacturers.

You can put a TB plug over the spigot, remove the switch from the back of the TB rack, tape over the ends of the wires and secure them somewhere out of the way.

That sounds like a great solution,I love taking parts off that have no purpose !!!!

You can do that, did it on my 84 K100RT then put it back, but my 83 K100RS also has this and I decided to keep it all original.

Thing is, my 83 RS has the engineering screws but seems to make a difference. My take is the early as in 83 has the earlier camshafts and valve timing and that may be the case as it is much more aggressive to ride. I intend to do a temporary disconnection to see if it makes a difference.

I do see the RS is the most economical of all my Ks, by a long distance regularly hitting 12.5/13 miles per litre, my K100LT doing 10 miles per litre, my K1100LT doing 10-12 miles per litre and my 84 K100RT about 10/10.5 miles per litre so there is a difference from 83 to 84..

Inge K. wrote:Have no experience with this vacum switch myself, but from what I have read on other forums...owners have disconnected the hose and not noticed any difference.

I suggest you do the same, and put a rubber cap at the stub....and it could be that it improves the engine cold running,,,if the tatty hose have a small leak.
But this could be tried first, and then we take it from there....

If I remember correctly the switch would advance the timing a few degrees to improve fuel economy, but it probably did close to nothing....since it was discarded after a short time.

Here is a picture of the switch (so you see where the hose ends):

Yup,took mine off and capped it but I am going crazyyyyyyy ! The bike ran about a week ago when I still had overheating problems.I got a new coolant sensor, a used cooling relay,removed the vacuum sensor and plugged the barb on cyl 1 on the throttle body.Bike won't start.No fuel getting to the fuel rail.open the tank ,took the fuel hose that goes to the top of the pump off the filter,pushed start... at this time I should have fuel squirting out of the hose,correct? but nothing.It's a new pump,it worked before,checked the fuse which seemed good,replaced it just to make sure.Even put the old cooling relay back in to make sure that is not the issue,but that shouldn't even have anything to do with the fuel pump,right? SOS !
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