Why does my twist grip not return smoothly ? Polite words fail me !
   I would like to think this a more obscure reason why.

It looks like its been in a vice. It is out-of-round by just under one Mill. 
   Something else for me to play with.   Dale

One thing I have had a couple of times was the flange on the rubber grip would be pushing against the switch block due to it riding up the throttle tube. I ended up gluing one of them but the other time just pulling it back along the tube till there was 2-3mm clearance solved the problem. Also on some assemblies there is a screw in throttle lock under and to the front of the housing. It's an aluminium screw with a head about 5c piece size.
Often it is just the grease is old and hard and it all needs cleaning, the cable should not be lubed as it has a teflon liner and will bind up over time if it is oiled.

Also... when the cable gets old and worn it can bind and it'll be hard to wind it on as well. If after checking Rick's suggestions it's still slow to return, check the cable routing or replace the with a new cable.

Check the crown and pinion teeth. They can spall and shed small chunks, then gall badly where the broken parts stick. Net result is that two or three teeth do not mesh correctly. These are the teeth that are in mesh when the throttle is holding approx 60mph/95kph. In my experience this can cause the throttle to both not open or close correctly from this point.

One of BMW's not-so-good ideas, I'm afraid, despite the longevity of the system across various models. I fitted a brand new pair after the original galled quite badly, then 15,000 miles later binned them as they were in the same state as the originals despite me looking after both the crown-and-pinion and the throttle cable.

Dale, what grease are you using?

I have the same problem, I've traced it to the bar end weight rubbing on the grip. If I loosen the bar end, all good, tighten it, and it binds. I believe the grip had swollen over time and is now too long. Time to buy some new grips.

Without the chain and cam hooked up, does the cable return easily?

T3CNO1D

T3CHNO1D wrote:I have the same problem, I've traced it to the bar end weight rubbing on the grip.

Bar-end weight should be adjustable. It fastens to an expanding bolt. Just loosen the screw, tap to loosen the expander and adjust the bar-end to stop rubbing against the grip rubber.

I fitted bar end weights to the k75c - I like the look - found that even moderate tightening expands the tube enough to make the throttle bind. It means that I don't need to bother with the throttle friction screw which I would otherwise be using on all longish rides

My RT bars have the expanding bolt but the RS bars I've just installed have a threaded fixing inside which the bar-end weight bolts to. No adjustment. To stop it rubbing on the grip I just moved the switch block/throttle mechanism a few mm to the centre so I can screw the weight on firmly.

Kaptain Holister wrote:My RT bars have the expanding bolt but the RS bars I've just installed have a threaded fixing inside which the bar-end weight bolts to. No adjustment. To stop it rubbing on the grip I just moved the switch block/throttle mechanism a few mm to the centre so I can screw the weight on firmly.

I've got the welded threads too, so I will try moving the switch block as well, isn't there a a pin that hold the switch block in place and from rotating?

Thanks all for the areas to investigate. 
   At the present the Handlebars are disconnected from the steering-head as i'm replacing the bearings, 
      checking out the front fork stanchions & the front discs need replacing.
   "Grease" is there a specific grease to use?

T3CHNO1D wrote:I've got the welded threads too, so I will try moving the switch block as well, isn't there a a pin that hold the switch block in place and from rotating?

Just the 4mm socket head from the front side (back of the switch block)

DaleRT wrote:Thanks all for the areas to investigate.
  At the present the Handlebars are disconnected from the steering-head as i'm replacing the bearings,
     checking out the front fork stanchions & the front discs need replacing.
  "Grease" is there a specific grease to use?

I just use Penrite Molygrease EP for everything except splines