After much thought I recently cut the black/white wire going to the TPS or butterfly switch as its also known as.
The bike is now much smoother when slowing down and I really prefer it this way.
BUT. Because the engine doesn't have the same engine braking the brakes need to be used a bit firmer and this is where my problem comes in. Have a touch of arthritis in my thumbs and after a hundred or so miles, my hands are getting a bit sore.
The intention was to install a switch to give me the choice of having it or not and was thinking about where to put the switch.
That's when I came up with the idea.
What if the black/white wire that was connected to the TPS was connected to the brake light?
If you were sitting at, say, 60mph and backed off the throttle but wanted a bit more engine braking. A light touch on either brake and the fuel shuts off and slows the bike down more. Below 2000rpm, no difference anyway.
Release the brake and back to normal.
I was thinking of running a temporary wire to try out the theory.
Unless I've sat up too late and someone can point out the bleeding obvious to me!

It has been discussed and ruled out elsewhere in the forum.

A preferable solution is to put the wiring back as original.
 Then, Re-set the idle switch adjustment so that with the throttle totally closed (as when slowing downhill) that the switch is just outside it's activation point, hence never closing in the off-throttle position.
In this way, you retain the OEM design on the wiring, you achieve your desired action & you maintain the wide open throttle enrichment on the switch.

There is an option in the BMW parts Frisch for a replacement front brake lever listed as "for those with smaller hands" that might be a good option for your arthritic issues????

32 72 1 457 058  HAND LEVER, BLACK, RIGHT   $53.91
Regards, Ibjman

Interesting about the brake lever but I'm not sure it would be a cure for me. The problem is in my thumbs and while the 8v brakes are effective, they do need a good squeeze to make them work.
Something on the lines of the two fingers jobbie on modern bikes would be the answer.
So the answer may be to reconnect the TPS and live with it or install the switch for situations where it would be helpful. I regularly do 300 mile plus days on mainly bendy roads and it can be a problem after a while. 
I don't remember the idea of connecting the brake light to the black/white wire on the TPS being discussed before.
Did anyone actually try it and why was it deemed to be a bad idea?
The only concern I have is that it mess up the ECU and maybe the fuel won't come on again when it drops below 2000 rpm or you release the brake.
In theory, it seems ideal, for me anyway. Slowing for a bend, need slightly more retardation, touch one of the brakes and the fuel cuts giving more engine braking. I notice that the brake light comes on with hardly any pressure on either brake.
Any other feedback?

Comberjohn wrote:Interesting about the brake lever but I'm not sure it would be a cure for me. The problem is in my thumbs and while the 8v brakes are effective, they do need a good squeeze to make them work.
Something on the lines of the two fingers jobbie on modern bikes would be the answer.
So the answer may be to reconnect the TPS and live with it or install the switch for situations where it would be helpful. I regularly do 300 mile plus days on mainly bendy roads and it can be a problem after a while. 
I don't remember the idea of connecting the brake light to the black/white wire on the TPS being discussed before.
Did anyone actually try it and why was it deemed to be a bad idea?
The only concern I have is that it mess up the ECU and maybe the fuel won't come on again when it drops below 2000 rpm or you release the brake.
In theory, it seems ideal, for me anyway. Slowing for a bend, need slightly more retardation, touch one of the brakes and the fuel cuts giving more engine braking. I notice that the brake light comes on with hardly any pressure on either brake.
Any other feedback?

 Hey Comberjohn,

You have a great idea about combining the brake light and the TPS.
I think that it's easily doable with the use of a relay.

I love the idea, and if you need help I could work with you on an auxiliary circuit.

CF

Thanks Bert. Was starting to think there was something wrong with my head.
After all, part of the fun of running the K is to tweak it in the never ending quest to improve it.
You are right about a relay. Hadn't thought of that. It would be the safest and easiest way to do it.
Power from the brake light circuit operates the relay and reconnects the TPS. Simple!
Was nervous about damaging the ECU but this would bypass the potential problem.
I have a couple of relays lying about. I'll rig up a temporary set up to see how it would work.

Ok, my memory isn't what it once was.......sorry for the mis-info.....must have been a different subject
Regards, Ibj....

Comberjohn wrote:Thanks Bert. Was starting to think there was something wrong with my head.
After all, part of the fun of running the K is to tweak it in the never ending quest to improve it.
Before I get too involved in it, do you think it do any damage to just connect a temporary lead from the black/white wire connected to the ECU to a point on the brake light circuit. Just to see how it would work.

Nothing wrong with your head other than thinking  

I have removed the TPS on my solo bike, but think that it would be good to re-enable it on demand.
You could put a switch/relay to enable it the normal way or use the brake light contact to enable it.
I will work on designing a flexible system and that should be easy.

CF

The problem of the throttle snapping shut and making it difficult to smooth out the ride can be sorted with the simple, quick (and cheap for 8v bikes. Not quite so simple of as cheap with the 16v models) addition of the throttle stop screw.





Just set it so that the throttle doesn't quite snap shut and slowly closes instead.

Yes, they're a great job. Had one on my last K.
Unfortunately, many earlier K's don't have the tapped hole to put it into.
It's a bit more than that anyway. The bike is generally smoother to ride without the TPS. Unplug it and try it if you haven't already.
Come over to the dark side.

just a thought

the front is used for pretty heavy breaking  and some trimming as well ....but I think all of us would be on the rear pedal when it comes time for slowing up and stabilizing the braking effect

the enigma in the tps ..is that it takes some time for the injectors to come back on throttle ...especially when trimming round a corner  with the front slightly pressed ( the deceleration whist on the tps function happens quite quickly in contrast  but not sure of the effect  without throttle roll back required and using a real quick switch on off activation ) and the jerkiness associated with this .

maybe there is a solution

unfortunately the front and rear brakes share a common circuit in parallel to the brake lamp

heres a suggestion  

 perhaps the rear brake circuit could be used for the trigger   what would be required is a double throw double pole relay

the first section of the relay could be used for the usual brake light activation ...but the second poles could be used for connecting the tps  activation (off the rear brake switch relay ) this would isolate the front brake activation of the relay and give a matter of selection between front braking alone and rear with the now tps injector cutoff function  in addition to braking
the circuit would need to the usual power feed to the switch and then relay but maybe a diode to stop the front brake switch  activating the relay as well ???


what im saying is to remove the activation of the relay from both of the switches ( usually in parallel ) on the way to the rear globe

does this make sense to some of you ? 

thought to add for the benefit of all

That sounds like a good addition, Charlie.
Would it be possible to take a feed from the rear brake switch alone that would activate a relay to reconnect the TPS?
Or maybe that's what you said anyway!
Come into a corner, light touch on rear brake and bike slows down when then fuel cuts out, leaving front brake for everything else.
Think the only way is to rig something up and try it out. 
Can't see anything dangerous as the brakes themselves are not affected.

yes in essence cj ....you would need to hold the rear pedal down for the duration though ...might be a bit tricky cause if you try to accelerate at the same time as the rear brake is pressed the injectors will be cut above 2000....  this I see as an unexpected fail on power when needed - expected  especially when taking corners above that magic mark of 2000  ...which is often the case ......whilst cruising rather than hacking ...no real issue I guess ...possibly an additional  switch in the dash for those modes huh ....with a nice clear led indicator for the "mode "


mechanical switch on down hills in the dash ... might work ......as said earlier

the beauty of the accelerator and tps control (as installed )  is that it is mechanically linked ...so when coming on throttle you have the switch already released

a very complex subject indeed

Comberjohn wrote:Yes, they're a great job. Had one on my last K.
Unfortunately, many earlier K's don't have the tapped hole to put it into.
It's a bit more than that anyway. The bike is generally smoother to ride without the TPS. Unplug it and try it if you haven't already.
Come over to the dark side.

 It's listed for bikes as early as 1983. I've not looked at the earliest Ks but as it also fits the R models that share the same handlebar controls, I'd have imagined that the hole is there, just still fitted with the plastic blanking plug. 

The bikes I have in my garage are a 16v and a K75S. I have set the TPS on both with a multi-meter and I cannot for the life of me understand the desire to disconnect or otherwise by-pass the TPS as neither could be smoother.

16 valve doesn't have the same tps and issues mike ...just the 8 valvers with the jetronic
not sure of the 75 s though .....is that the early or late model ?  and did the those later models have a modified motronic ?

charlie99 wrote:16 valve doesn't have the same tps and issues mike ...just the 8 valvers with the jetronic
not sure of the 75 s though .....is that the early or late model ?  and did the those later models have a modified motronic ?

 Yes I know that the TPS operation is different for the 16v but I've never found an issue with the TPs operation on any pre-16v models (three or four cylinders).

The K75 has L-Jetronic. 

The issue seems to be that the abrupt shutting off of the fuel delivery when the throttle is released makes it difficult to modulate deceleration and braking.

This isn't much of a problem when braking to a standstill but when road conditions require braking before a lower gear selection, closing the throttle (to the point where the TPS shuts off fuelling) results in more deceleration than is either desired or necessary. The same thing affects 16v bikes.

The simple fix is the throttle stop screw. Set it so that the throttle action is slowed by the friction of the nylon tip or set it so that it is a "positive close" action. I know that many people don't like the sensation of a "sticking" throttle. It used to be the norm and it is quite easy to get used to.

All the Ks (and Boxers before them) I used to ride at work had the screw as standard. I soon learned that it was worth the five quid to fit them to my own bikes (nearer 50 quid and much more work to fit to 16v bikes).

I'm just suggesting that the 8v bike version is worth trying before modifying the TPS.

I certainly would not use it in conjunction with the brake as I will feather and drag the rear brake coming out of a corner hard on the throttle and that is the very last situation I would wish to suddenly lose power.

RicK G wrote:I certainly would not use it in conjunction with the brake as I will feather and drag the rear brake coming out of a corner hard on the throttle and that is the very last situation I would wish to suddenly lose power.

 Sorry. That's lost me completely.

Use what? The throttle stop screw?

All it does is decrease the speed at which the throttle closes. It can be set to no effect or so that the rider has to close the throttle instead of allowing it to spring closed. The latter is variable according to need or preference.

I don't want to hijack the thread but why on earth would anyone one want to drag the rear brake when exiting a corner?

Seems to me like the switch on the dash is the way to go..Idle switch on or off..simple

as for the throttle stop screw, that's an idea too..I was rising a friends old R900 ( I think it's called) with no return spring, and it was weird, but I kind of liked it..

My K75s has a small white nylon what looks to be a screw, where this throttle stop screw would be..It's flush with the housing..What's with that I've been wondering for months?

Jim Miller wrote:
My K75s has a small white nylon what looks to be a screw, where this throttle stop screw would be..It's flush with the housing..What's with that I've been wondering for months?

 That's it. Hoik it out and in goes the screw.

Motobins part # 61183 £6.50 to those who don't have to pay the dreaded VAT.

MikeP wrote:

Jim Miller wrote:
My K75s has a small white nylon what looks to be a screw, where this throttle stop screw would be..It's flush with the housing..What's with that I've been wondering for months?

 That's it. Hoik it out and in goes the screw.

Motobins part # 61183 £6.50 to those who don't have to pay the dreaded VAT.

 Oh ok..thanks...Yould think that could come with the bike...how about a metric bolt and a spring..lol

If you look at that part, it has a nylon/whatever tip. Not sure what a steel bolt would do to the twistgrip mechanism...

RicK G wrote:I certainly would not use it in conjunction with the brake as I will feather and drag the rear brake coming out of a corner hard on the throttle and that is the very last situation I would wish to suddenly lose power.

I would not use the brake switch to operate the fuel cut out.
If I am riding hard and I mean 10/10 I drag the rear brake comming out of a corner as I turn the throttle on to full, it makes it far less likely to step out at the rear when I suddenly give it a handfull and then release the brake slowly. Doing it that way means you can get on the throttle a bit earlier than the rest of the gang.
I was taught how to do that by one of Australia's great riders the late Greg Hansford.
It works for me as that is where I have always gained a few meters on anyone trying to keep up or get past on a racetrack or when having a bit of fun on the road. I dont indulge quite as much nowdays as I have a bit more respect for my hide but sometimes I get a bit carried away.
Mind it is a bit unnerving for anybody behind to see a brake light come on as you exit a corner.

I knew that I had seen a reason why the brake switch trigger idea might not have been a good idea, discussed before. 
It may have been in another context.....
Regards & thanks Rick......Ibj...

Hey Rick, when you are on the gas the TPS will be operating as normal, as in connected up ie no fuel cut 'cause you are on the throttle.

Ghost who rides wrote:Hey Rick, when you are on the gas the TPS will be operating as normal, as in connected up ie no fuel cut 'cause you are on the throttle.

You are quite right there Gordon when I analyse it. As soon as I open the throttle it overrides the switch doing anything.  I was looking at it as if the TPS closes the switch when the throttle opens,when it actually closes the switch when the throttle closes.
But what I do still stops it sliding around as I give it the noise.
I wont say try it because till you get the knack of timing it right things can get a bit hairy.

I can't say that I have ever had a real problem with the TPS cutting in and out but I don't do much stop start riding in city enviroments any more, there isn't even any traffic lights in Stanthorpe and that's why I like the place.

Agree Rick, it's a "first world " problem. We in the sticks say... HUH? Only joking.
 
I have followed these threads for about three yrs now and realise what everyone is on about, however

I haven't been tempted to do the disconnect as yet. Maybe it's because I have the triple and you guys are

riding the greater torque of the K100? I learnt to keep the revs on when downshifting and the box rewards me 

with slick (relative) shifts. I'm not talking boy racer here 'cos i'm far from that. I do luuurv the feeling when 

the engine braking kicks in, and the sound!

Mike P is saying the same thing I think but I want the throttle stop for long distance riding as on my old girl.

Comberjohn is right on the money in my humble for the best compromise, good luck with it. Between you, 

CF and Charlie it should be the Bee's.

I was thinking about this problem for few days and read the pro and con.
I have removed the TPS on one of my bikes. I found the riding smoother, but sometimes I miss the engine brake.

One of the problem pointed about wiring the TPS with the rear brake is that you will not be able to get any power if you apply the brake.
The other problem about controlling the fuel injection with the brake light is that if you don't shut off the throttle, you will cut the injection, but your engine will still suck the maximum of air and next to no gas.


My solution is as follow:
Having the TPS working normally ONLY when the brakes ARE applied.
Being able to have the TPS working normally even when the brakes ARE NOT applied.

You will need a relay, a rocker switch and a diode.
The black/white wire of the TPS has to be spliced and each side connected to the contacts of the relay.
The coil of the relay is energized with the rocker switch or the brake light. (You need a diode to avoid having your brake light ON when you want to have the TPS active.

If the manual override switch is ON:
The coil of the relay is energized and the TPS will work on normal mode. The Diode will prevent the power to turn the brake light on when the relay is energized. Braking will not have any effect on the system since the TPS is already active.

If the manual overide switch if OFF:
When applying the brakes (front or back), the relay's coil is energized and the TPS will work as normal. The FI will be cut ONLY if you shut off the throttle.
Braking will not affect the EFI if the throttle is slightly open.

If you really want to turn the TPS off, you will need another switch on the wire coming from the brake light.
In this case, the system will become complex to operate.  Why would you like to shut off the TPS if you are shutting off the throttle and trying to stop

The other point is that controlling only the relay's coil with the brake light will not draw enough power to affect the bulb monitoring unit.

With this system, the full throttle switch is always working as intended and the engine brake (idle switch) can work as normal or only when you brake and shut off the throttle. .

I am waiting for your comments.

CF

a good solution bert

maybe I have been over thinking it .

in addition to your thoughts possibly a double pole double throw centre off switch (if such a thing exists ) .....up position = tps with braking ....down = normal operation .... centre = off all the time ?

Why not put the over ride switch where you have cut the wires?

nboogie wrote:Why not put the over ride switch where you have cut the wires?

The switch has to be easily accessible. You install it where ever you want but the dash would be the best place.

You got it Charlie  

Here is a different circuit with the same principal. Replacing the switch to a single pole double throw with center off, eliminate the need to install a diode. You also have full flexibility for controlling the TPS.
 
To cover all aspects of controlling the TPS, you should buy a

SPDT with center off switch (Look for model K103 SPDT C/Off)

Top position would be TPS working as normal.
Center position would be NO TPS
Bottom position would be TPS working only when you brake.

This should makes everybody happy.

nboogie wrote:Why not put the over ride switch where you have cut the wires?

The switch has to be easily accessible. You install it where ever you want but the dash would be the best place.


Did not mean it literally; connect switch to where wires are cut.
The diagram shows the bypass connected straight from the battery unfused/unswitched. If the bypass is not switched off the relay will be energised 24/7.

Rnboogie wrote:

nboogie wrote:Why not put the over ride switch where you have cut the wires?

The switch has to be easily accessible. You install it where ever you want but the dash would be the best place.


Did not mean it literally; connect switch to where wires are cut.
The diagram shows the bypass connected straight from the battery unfused/unswitched. If the bypass is not switched off the relay will be energised 24/7.

You are perfectly right  
 I modified it on my latest schematic. You should use a switched/fused power source.
It's easy to pickup the power from the tail light or the parking light.

I was originally trying to work on the principal, and as expected, somebody (Charlie) came with an improved idea. This is why we are successful: Everybody question and come with corrections or improvement.

o.k ; thats sorted, what next?

Rnboogie wrote:o.k ; thats sorted, what next?

 Who will try this solution first? ComberJohn?
This maybe one of my winter project, but for now my priority is to ride. (We had an ugly spring + I spent a month driving in Europe. I rode only 5K on the bikes this year).

CF

I'll plan to install this circuit on my K75 rebuild.

BTW, I think the diode and SPST switch circuit is more elegant than the SP3T switch circuit.  That's just me.

That's what I like about this forum. We can discuss 'off the wall' ideas and look for solutions or drawbacks.
I like the ideas put forward. Very elegant.
Just hope Ducati don't steal the idea for next year's model.
Agree with you, Bert. This isn't the time of the year for fiddling about when the sun is shining.
I would like to try out the basic idea soon, though. I think I may rig up a temporary relay to bring in the TPS when the brake light comes on.
Might make it a pig to drive and would rather try it out before going too far down the road of modifications.
I'll post what happens when I try it out unless someone else does it first.