Hello, I have owned a 1987 BMW "hybrid" 75C meaning it is titled as a "C" but has a K75T headlight surround.  (I believe this surround is identical to the one on the Naked K100).
I am joining this forum because it has a K75 section, and also because there is so much similarity between the K75C and the K100.  
I am 78 years old, and took up biking again in 2008 after being away from it since 1952.  I almost always ride alone, due to the fact that my schedule does not permit me time to take long rides with groups.....(I am caregiver for my good wife who is paralyzed and cannot speak as a result of a massive stroke in 2005).  I also have a 1994 Honda Magna VF750C, which has a V4 engine and runs almost as smoothly as the K bike..

I have had bigger bkes than these and sold them off as they were too heavy for me...I bought a nice trike recently and sold it within two weeks of buying it because it was too tame for me..

Thanks for allowing me to join in.

Bob

Hi Bob,
                  Welcome to the Forum mate. 

Nathan.

Welcome.

The K75T was a North America only model. BMW NA put a K100 headlight surround on them along with a handlebar mounted windscreen and RT handlebars to make them more suitable for touring.  They were all manufactured and titled as Cs.

Hi Bob and welcome to the forum too. Good to see you on the K75 and hope you get a few more years out of it. But, a big but, when it gets too heavy get a trike because the thing you will miss is the wind in your hair and smile on your face.

You are a bit far away from me to meet up but many years ago I had a good friend with a love of sailing but his wife felt it unwise for him to go it alone because of a bad heart. I stopped one morning to help him with a small car problem and having bled his clutch for him he said what a nice day and how he would love to go out in his lovely little 17 foot cruiser but the wife wouldn't let him. A quick phone call to the office led to the two of us going out for one of what was to become quite a few good sailing days and fishing for our lunch.

So if anyone is near you maybe you might get an occasional riding buddy because I am sure you have lots of stories to tell.

The forum here is a good sociable one too and we enjoy lots of nice banter and chat.

Thank you for your warm welcomes....

I hope to continue riding for a few years.....I plan to take a trip of a few days on the scenic Blue Ridge Parkway in North Carolina and Virgina sometime this year...Perhaps I can find a riding buddy for some of the near-home rides.....

I ordered a windshield this morning.....National Cycle N2595.....There don't seem to be many choices for the K75T or any other K75 for that matter....The wind does not bother me, but it makes riding more tiring..

I have a problem with the throttle.....Seems to be in the cable...Twice in the past few days it has just "stuck" and I could not "turn it off" and it made the bike go faster and faster and the throttle handgrip was essentially frozen.......the only thing I could do was hit the kill switch, then slow down and put the switch in the "on" position and release the clutch and the engine caught and ran ok again...This is scary..I'll take it to the wrench guy this week....I so not feel confident to address this on my own....The first time my mechanic pried the handgrip about 1/8" rearward and it was fine for a few days...yesterday it did it again despite the handgrip having been moved a bit rearward....Any ideas of the cause of this problem?  

All regards,

Bob

The cables have a Teflon-sh type lining in them which may be wearing or there may be too much of a bend in the throttle cable routing somewhere.
 
1)     If the throttle sticks open while riding then you can reach down with left left hand and push the throttle back down to idle.

2)     Do not spray lubricant in BMW cables as anything you spray in there usually degrades the cable ling and deteriorates it.

Thank you for tip on the cable...I tried a small adjustment to provide more slack today but it still sticks intermittently....when I force the throttle to close it takes a bit of time for engine to slow, whereas, when not sticking it snaps back and the engine slows quite rapidly....

In addition to seeing if I can find a shard bend in the throttle lcable, I will start to search for replacement cables..My guess is that cables might only be available as OEM   from BMW.....

Best,

Bob in North Carolina, USA

Hi Bob,
I had a similar problem with my 85 K-l00. Occasionally sticky throttle. When I blipped the lever at the the throttle body it was fine so I also suspected the cable.
While dismanteling the twist grip itself I discovered a previous owner had done a DYI cruise control!  A friction type washer thingy that decreased the twist grip spring return. What we used to call a "suicide throttle".
Never take anything used at face value! I only trust things I have wrenched myself.
Hope this helps,
Rob

Thanks for comment about Suicide washer....So far have not determined where the throttle body lever is.....(Color me dumb, I guess)...

I'll keep plugging along....

Regards,
Bob

Bob, there are down-loadable manuals on this site. Have a look at the twit grip drawing. The cable is indirectly connected to the twistgrip with a little chain piece and a cam wheel situated under the cover with the big screw just right of the front brake reservoir. If you open that and take the cam wheel off have a look if the handle turns easy or if the cable pulls/returns easy. That'll tell you where to go next. There are after-market cables, but the original BMW ones are the best (for me) and if you do it right you don't need to replace them too often.

Thanks for tip on chain thingy inside the right hand controls...I'll give it a try....

Another person said that I could reach down with my left hand and move the lever "gizmo" on the throttle body and I have looked and looked and see nothing that looks like that..

Bob

Inge - Is that a carb'd K75?

  Hi Bob !

Very welcome to this place; you'll see: all 'good guys' over here.
I hope you enjoy your K as much as possible and get this throttle-problem fixed soon !
Enjoy !

Jos.

duck wrote:Inge - Is that a carb'd K75?

Red and lengthened induction tubes doeth not a carb make

Please note I did  not say "current progress"......  .  Stay tuned...

Thanks Inge for posting photo showing precisely where the fuel lever is located on the throttle body..

Thanks also for the information on removing the cover from the control just next to the twist grip..I did that and the innards looked quite good.....the teeth on the front end of the twist grip andas well as those  inside the "control box" looked fine...It was well lubed with moly paste.....I looked over the chain thingy and it was fine too, per my eyes..

Then I put it back together and fired it up...Engine raced at full throttle...whoops...my bad.....shut it off pronto and took the cover back off and noted that there were a range of options to line of the teeth and the twist grip and the inside of the "control box"....Gave it my best guess and tried again...this time I did not try to start the engine, but the twist grip only would go about half of the previous arc, and also stuck there......so I tore it down again.....I looked in the Clymer's manual to see if there were instructions on how to line up the teeth and found nothing....so, before doing any more, I am asking for info from this forum..

I am assuming that if I start the assembling with the chain pulled to its full length, but not any further, before seating the teeth together, that I am on the right track..if not, please advise...Other than that, I don't have a clue.

The good news is there is a BMW certified mechanic who works for a Honda Dealer where I trade and he may be able to come over on his off work time to take a crack at it...I have no way to transport the bike to the dealer so that is the option I am pursuing at the moment...

Meanwhile I do have another bike that I can ride...

Best,

Bob in North Carolina

Bob, there's a mark on the twistgrip and a mark on the cam. They should be aligned to get it right. Little line on the grip and the cam wheel should be quite obvious. I haven't got the bike any more otherwise would take a picture. Again, take the cam wheel off and then try the grip or pull at the cable to see where the issue lies??

What I've found works well is to clean all old grease out of the throttle gears and then give it all a good bath with silicone spray lubricant. Moly is good stuff but is not a panacea that you want to use everywhere.

Thank you for additional comments and suggestions...I cleaned up the "old" moly paste with silicone lubricant and found the two marks showing where to line up the twist grip and the thingy it goes into....

After drying things out I applied fresh moly paste..

I could lift the cam wheel off its axle but was unable to remove it completely....The parts "look" ok to me.

I did not try to remove the rubber boot that surrounds the cable at the front of the control box...

After cleaning and lubing the "works" again, I tried a number of times  to move the twist grip with my right hand while holding two fingers of my left hand down on the cam wheel, but it jumped out of its course repeatedly.   So I put the cover back on and twisted the grip and it took a heck of an effort to twist it....(Same thing happened after I took the cover off yesterday and put it back on and tried to twist it.).....(I tightened the keeper screw on the cover just snug even though it was very tight when I first dug into it a day or two ago..)

So I got the bike started and took it for a ride on a lightly-travelled road for about ten miles....I tried various things, opened the throttle all the way in fifth gear a few times and it almost always did not come back by itself..Sometimes it would decelerate when I twisted the throttle back to idle and sometimes it kept running at full throttle when I twisted the throttle back to idle....I used the kill switch to get it to shut down, and then coasted a ways and got it to start again by switching it back on.....Dangerous for sure and not acceptable to me......There is a significant binding when twisting the throttle to open or close it...At very low speeds in lower gears the throttle came back by itself about half the time. 


There is about a third of an inch in back and forth "play" when the twist grip is at the idle position and the twist grip moves back and forth very easily at that point.....(no binding).

Now that I have it running, I can take it to the dealer where the BMW certified mechanic can fix it.  However, I hate to give up without figuring out what is causing the binding, as it did not do that previously anywhere near to the extent it does it now...

Thank you for continuing suggestions..

Bob in North Carolina, USA

When you have the throttle tube off, also spray down the handlebar the tubes rotates on with silicone.  And the return springs down on the throttle bodies.

I conclude you have already tried the throttle rack manually and it snaps tight. If it isn't the grip itself, tested as Duck says above, the only thing I can come up with is that the throttle cable somehow is nicked. I don't know what bike you have, as it is not in your signature, but can you try to follow the throttle cable with your hand or hold one end above the throttle bodies and another where the cable comes out of the frame at the steering head and see if you can pull it around a bit.

Sounds to me like the gears are worn and riding over each other and binding.

Still more thanks for good comments...Bike is a 1987 BMW 75c fitted with naked K100 round headlight surround...I think that it is a USA only K75T.....

Twist throttle turned freely until I dismantled the twist grip and the control "box" adjacent to twist grip...

Intuition tells me that the severe binding at present is because gear teeth are misaligned somehow....They do not, however, appear to be worn............cover for control box adjacent to twist grip was very difficult to get back together....the little tab at the trailing edge of the cam cover makes for the difficulty...

I do not believe the twist grip is binding on the handlebar...it is nicely lubed...
 
Prior to this past few days the throttle posed no problem since buying the bike a few weeks ago..I rode enough that I used up 3 or 4 tanks of fuel.....Then a week ago I had the dealer switch the more sporty handlebars for the RT closer-to-rider handlebars that the previous owner said were on the bike when he first bought it.....Cables seem to have plenty of room, although throttle cable looks like it could have used another inch or so...I am guessing that there is a kink in the cable somewhere..

I checked the throttle release lever down by the engine and it worked fine the other day...However, after dismantling it and cleaning and lubing the gears in the "control box" yesterday the lever at the bottom of the cable does not return, although it can easily be pushed to the closed position by my finger....

BMW certified mechanic is coming to the house on his day off from the shop on his day off and I hope and expect he'll be able to solve the problem...

Regards,

Bob

OK, well, let us know? If you would have told us about the changes to the handlebar..... I think they janked the cable out to get the space needed to fit the other handlebar and now the cable is nicked or with a harp curve.

Well I found a tutorial  on sticky throttles on one of the BMW  forums and realized I hadn't taken the "works" apart properly..
Now I have done that and have gotten the cam wheel and chain out of the place where it was installed.....cleaned them up a lot better....Three teeth on the cam wheel are somewhat worn, although not all that badly  it seems to me.  The teeth on the front of the twist grip seem to be in very good shape..

I ran out of energy just a bit ago and so have not buttoned it up.....it is a bit of a struggle to get the top end of the cable attached back to the end of the chain "keeper"....I'll jump back in tomorrow...

Question, where should the little O ring be placed?

Thank you,

Bob

Which little o-ring???



There is no little o-ring in the throtle cable assembly  

Before you button it up first check that the cable snaps back, using  a pair of grips pull the exposed cable end lug out as far as you can (no force) then let it go, it should snap back, if not your problem is with the cable routing or down at the throttle bodies. If it does then look at how the accelerator grip assembles, it should rotate smoothly. 
 

Thank you for additional comments..

On my bike there is a small oring on the throttle cable assembly and it does not seem to be a "fit" anywhere among the other parts.....thanks for drawing..

I tried pulling the cable out with a pair of pliers and got mixed results...Thus I suspect the cable is nicked somewhere and sticking.....by "mixed" results I mean that the cable sometimes seemed to resist being pulled out, and sometimes would snap back, and other times not...I also opened the throttle lever on the throttle body at the bottom end of the cable and it snapped back with alacrity when opened all the way, and now and then not so briskly when only pulled part way out..

As mentioned in an earlier posting I have a mechanic with a BMW certification coming over on Tuesday afternoon to jump in.....I may try to button it up before he comes and see how/if it works, but may just leave it disassembled....

I very much appreciate all the tips and questions and comments..

Bob in North Carolina

Well, energy started to flow again this afternoon (it sometimes stays dormant at age 78) and I cleaned up the controls inside the throttle box again, oiled the parts with a light lithium grease and put it all back together......took for brief spin.....it still is sticky but did not stay stuck.  I only rode three miles or so and it probably could use a longer test...In any event, this condition is not gonna make it, and I am going to have it repaired with whatever new parts may be needed...Again, BMW qualified wrench is coming over in a day or two to have a look and so it should not be too long before it is in the shape I want it to be..

I'll let you know what all needed fixing when it is all done...

Again, many thanks,

Bob in North Carolina, USA
1987 BMW K75.

Happy to report bike is fixed..it was a puzzler.....the wrench is a very perceptive mechanic....turns out there was a plastic coating on the outside of the steel throttle cable and it is impregnated with Teflon to allow it to slide inside the loose plastic sheath that covers the cable top to bottom...after my false starts and his false starts he finally figured it out and fixed it..
(You can see a photo of the wheel on reply number 12 from Inge)

Picture this....rope going through a pulley of substantial diameter so that the rope can wind up on the pulley..


Ok:  At the bottom end of the throttle cable there is a wheel reminding me of a pulley and the cable is pulled onto that wheel when accelerating....upon letting off on the slight pressure needed to hold the throttle open, there is a spring that unwinds the cable from the "wheel" I mentioned and it returns the throttle at the handlebar to idle.....


It turns out that  the Teflon coated cable was getting wound onto this wheel about 5/8th of an inch and upon releasing the throttle twist grip on the handlbar the slight width of that coated cable was binding against the inside of the wheel......


The wrench guy pulled out a knife, skinned off the bottom 5/8th inch of the plastic coating and the throttle now returns to idle every single time I release it...

I am very pleased with the results....Yes, there was normal wear on the mating surfaces of the "works" of the throttle gears at the top of the cable, but they did not cause the problem...

All's well that ends well.

Bob
1987 K75C

I had that happen and ended up having to replace the cable as it will happen again as the inner Teflon continues to slide down the cable.

Good work Bob and The Wrench.

I won't say it is something 'new', but it certainly is something I have not heard of before.

And now you know all the 'other ways' to fix your throttle if it sticks again.