BMW K bikes (Bricks)

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roach374

roach374
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Silver member
So I *finally* picked up my '93 K75, and noticed that the throttle doesn't return. That is, when I accelerate, I can't just let go of the throttle and have it snap back. I have to twist forward to come off the throttle.

So my question is: a) Is this normal? (I assume not, but want to be sure). And b) the parts fiche offers two different "Bowden cable" options (with two different lengths). Is one for throttle pull, and the other for push? what's the right part number to have the throttle return normally?

(I've already looked at the sort of "cruise control" screw underneath the throttle, removed it completely, and it has no effect.)

    

robmack

robmack
Life time member
Life time member
When you twist the throttle, it should return quickly when you let go.  There should not be any drag.  There are several possible causes:
- bind in the Bowden cable.  Check for kinks and sharp curves in the cable routing.  It should be a smooth run from the throttle to the actuator cam.
- dirt in the gearing mechanism on the control assembly.  Open the cover to the gear assembly and clean out any old grease.  Regrease and check for any gear binding
- dirt between the throttle tube and handle bars.  Remove the throttle assembly and check for dirt.  Clean the handle bars and clean the inside of the throttle tube.  Check for any burrs and smith them down if found
- the bowden cable has been lubricated by mistake.  If possible disconnect the bowden cable and check for easy movement of the braided cable.  If it is stiff, then replace the cable.  Never lubricate the throttle cable or the clutch cable.
- sticky throttle body arm.  Disconnect the bowden cable and check the throttle body actuator for free rotation.  Sometimes the TPS switch is misaligned and binds the actuator.  Make sure the TPS is adjusted properly

There are two Bowden cable lengths - one for RS models and one for RT/LT models.  The latter is longer than the former


__________________________________________________
Robert
1987 K75 @k75retro.blogspot.ca
http://k75retro.blogspot.ca/
    

Dai

Dai
Life time member
Life time member
One more: the handlebar weight may be hard up against the throttle tube. If it is, slacken off the allen bolt and pull it out very slightly.

I'm not entirely in Robmack's 'don't lubricate it' school but with a very narrow proviso. The standard cables have a teflon lining which will swell and stick if a normal cable grease is used. The downside of not lubricating is that the bottom end of the clutch cable will grab dirt and pull it up inside. That can form an abrasive paste that will stiffen up the cable action and will eventually grind through the inner cable. Flush the clutch cable with an inert silicon-based lubricant. The thottle cable doesn't suffer in the same way because the operating quadrant is hidden away from flying crap.


__________________________________________________
1983 K100 upgraded to K100RS spec, 1987 K100RT
Others...
1978 Moto Guzzi 850-T3, 1979 Moto Guzzi 850-T3 California,1993 Moto Guzzi 1100ie California
2020 Royal Enfield Bullet 500
    

Laitch

Laitch
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Life time member
If the throttle grip has been pushed too far onto the throttle tube, the flange on the grip will rub against the switch housing inhibiting quick return of the throttle. Check that too. The grip can simply be pulled slightly outward along the throttle tube so its flange quits rubbing.


__________________________________________________
1995 K75 81,000 miles
Question about throttle return cable on a K75 Usa-lo10
    

MartinW

MartinW
Life time member
Life time member
I was still on my original cables until this year when I had to replace a throttle cable. The OEM clutch cable 170,000 K's is now 28 years old. As per Dai don't use cable grease or WD40. I have been lubricating my cables with a PTFE based lubricant called Tri Flo for the last 22 years. I lubricate it every 12-18 months flushing out the cable with Tri Flo until it runs clear. It is also important to lubricate the clutch and brake lever pivot points and nipples with suitable grease. The clutch shaft has also been fitted with a grease nipple and is greased once or twice a year. My 75 is fitted with the clutch activated side stand retraction, which if used can put extra strain on the clutch cable, I avoid using it. I've always carried spare cables and I've used them twice both on mates bikes.
Regards Martin.


__________________________________________________
K75s Hybrid
    

roach374

roach374
Silver member
Silver member
Thanks everyone for your help! Sounds like there's only the one cable to worry about, so I know where to look now.

    

roach374

roach374
Silver member
Silver member
So after taking apart the throttle assembly, it looks like the assembly itself is a bit gummed up with 30-year-old grease and grime. I'd like to take it all apart and clean it, but the throttle tube doesn't want to come off. I think there are wires running inside it for the heated grips, and the shop manual (which is dated 1988) doesn't talk about how to disconnect those, to be able to take the throttle tube off.

Anyone got an updated shop manual for '93 models or later that might show those steps?

    

Laitch

Laitch
Life time member
Life time member
roach374 wrote:Anyone got an updated shop manual for '93 models or later that might show those steps?
What you'll need a shop manual for is removing the tank. Laughing The grip wires are plugged into connectors beneath it. Then, if your heated grip setup is OEM and you want to remove the whole shebang to clean the end of the bar under the tube, I think you'll need to snake the wires up through the hole in the bottom center of the bar, which means you'll might need to remove or loosen the bar so you can see what you're doing. You won't need to pull the wire ends into the bar if you're just trying to clean the throttle gear itself. The throttle gears couple as described in the '88 manual. The procedure offers a great opportunity to clean both sides of neglected 30-year old electrical connectors wherever you encounter them.  cheers

Here's what's at the end of the trail. The wires in the grip and throughout could be tender so don't treat them like hawsers.
Question about throttle return cable on a K75 Heated10Question about throttle return cable on a K75 Moorin10


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1995 K75 81,000 miles
Question about throttle return cable on a K75 Usa-lo10
    

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