This relates to my new to me 1967 R50/2.
The throttle action is stiffer than I expect and does not spring back to idle when released.
The question, before I tear into all of it: Did bikes of this year have neutral return springs so I should expect the throttle to return to idle when released?
If it's working as original, it will not snap closed when you release it. There is a spring blade in the throttle assembly that holds tension against it and theoretically, it will remain open until you turn it back. I say 'theoretically' because in my experience, it will gradually close. Often, that spring gets lost or discarded. The fact that your throttle stays open suggests that yours is still in place.
Some owners (including me) prefer the /5 throttle/brake assembly, which has a stop screw that lets you lock the throttle. This is handy when cruising at a steady speed and can save you a lot of wrist fatigue. The /5 version also has a brake light switch for the front brake, which the /2s do not have.
Enjoy your R50!
It's the /2 version of a cruise control. Duane has a picture on his website:
My R69S throttle snaps closed...the PO must have removed it or it is broken...I wish I had it!!
I'm pleased that as I learn about this bike every single thing seems to be stock, with the exception of the 12 volt upgrade which I do not begrudge at all! The headlight is BRIGHT.
Are you using the 6 volt bulb?
Even though the throttle will never snap back by itself, you might want to take a few minutes to check the adjustment. Remove the throttle cover and observe the position of the throttle, the cam, and the chain. You want to make sure the chain has no slack in it when you begin to rotate the throttle which pulls the chain which begins to operate the throttle cables. If there is too much slack, it will feel sloppy and there will be a delay in activating the throttle cables. You might also want to remove the throttle cam/chain assembly, clean it, and give it a fresh lube. If this hasn't been done in awhile, it could be contributing to the throttle's stiff feeling.
Enjoy your R50. Isn't it a sweet little ride?
Adding to what R. D. said, lube the cable as well. If this has not been done in a while, it can get gummed up inside the sheath, and this will make the throttle response "sticky." It won't snap back, but it should operate smoothly in both directions.
Some cables don't need lubrication, especially if they're BMW cables. IIRC, the throttle cable is teflon lined...lubing will only serve to attract dirt and result in stiff action. Lubing can be done as a last resort, but in the end, it's better to get a new cable.
...and to think, I bought one of those nifty little cable-luber thingies. I guess it's a last-resort cable-luber thingy.
I still have a couple of cable lubers around somewhere from back in the day. I keep thinking they'll be useful for something some day but I haven't had need for them. At some point, BMW went to Teflon cables - - maybe along about 1980 or so (?). Some time ago, Richard at Bench Mark Works told me that replacement vintage BMW cables that have the white stock numbers on the sheath do not need lubing. Nice improvement.