'58 R50 Throttle Issue

First post. Qualifier: I have been working on BMW's for over 50 years and have owned, ridden and raced countless bikes during this time. For the last 25 years, I have been building National Championship Winning BMW Race Cars.

About 30 years ago, a friend gave me his '58 R50 as the original owner in original good running condition. Could have a hundred thousand miles on it from him.

When I rotate the throttle grip, it moves about half way prior to engaging the carb slides. The problem is when I come to a stop, I rotate the grip fully forward and the bike then stalls. However, I've gotten used to rotating it forward slowly to the point where it still has a normal idle speed.

I have 2 of the blue factory shop manuals and the original blue owners manual. I followed the instructions regarding setting up the throttle grip/gears/chain to the cables. There is the proper 2mm
setting on top of the carbs where the cables enter.

I'd love to have it so when the throttle grip is fully forward in the stop position, the motor idles there. This would also fix the dead space from full stop/rearward to actual engagement of the slides.

Appreciate anyone who could advise the fix for this. Rest of the bike is great!

Thank you.
Jim



OK, not sure if I'm doing this correctly, but here it goes.....

I disassembled the entire throttle grip throttle, including sliding the grip off of the handlebars. I pulled the cables out of the housing and confirmed smooth movement as well as good spring return action in the carb slides. I cleaned everything with brake clean and an air gun. Laid everything back on according to the instructions for timing. I noticed that the chain had some slack with the marks lined up and the throttle grip in the correct position. I started thinking what difference does it make if I rotate the gear rearward to take out the slack. Going with this thought, I looked at the underside of the gear and there is a mark scribed from the factory 1.5 teeth forward from the mark on the top of the gear. I scribed a mark on top of the gear where this mark is and laid the gear/chain on the assembly. Chain slack gone. Sooo, I removed the gear and the grip, packed heavily everything with wheel bearing grease, and did a final assembly and now when you move the throttle rearward it only moves the slack in the gears. I am now going to set the cable adjustments now then final carb adjustments when the motor is warmed up a little bit.

Thanks to all of you for being there, I'm sure I'll be back again.......

Welcome to the forum! Sounds like the throttle tube with the teeth are not properly meshed with the cam that is in the throttle perch. Also that cam with small chain in the perch needs to be started out in the right position so there isn't any slack. But it sounds like you've been down that path. Hmmm...you might look over Duane Ausherman's page on throttles...go down about half way to a section titled "Magura throttle gear adjustment" and see if there's any new info there. Let us know what you find.

There's nothing magic about the set up. It's all about getting things in the right position before that cover for the cam/chain is put on.

https://w6rec.com/bmw-motorcycle-controls-and-cables-adjustment-and-replacement/

20774 said:

Welcome to the forum! Sounds like the throttle tube with the teeth are not properly meshed with the cam that is in the throttle perch. Also that cam with small chain in the perch needs to be started out in the right position so there isn't any slack. But it sounds like you've been down that path. Hmmm...you might look over Duane Ausherman's page on throttles...go down about half way to a section titled "Magura throttle gear adjustment" and see if there's any new info there. Let us know what you find.

There's nothing magic about the set up. It's all about getting things in the right position before that cover for the cam/chain is put on.

https://w6rec.com/bmw-motorcycle-controls-and-cables-adjustment-and-replacement/

Click to expand...

thank you for your time with a reply. I went to the thread you suggested and have bookmarked it. Quickly perusing it, I "think" I've done everything properly but I have a better understanding on how it all works with the gears.

I'll open it up tomorrow and start from Square 1 using his instructions and looking at the pics in the factory shop manuals.

I really appreciate all of you for this resource. This is my first post in any forum.......

Jim -

You sound pretty resourceful, and you are doing just fine on the posting front! We'll be here!

20774 said:

Jim -

You sound pretty resourceful, and you are doing just fine on the posting front! We'll be here!

Click to expand...

Thank you, hopefully I'll be able to return the favors at some point......

Including your location in your profile could help if you need a second set of eyes. There might be a vintage BMW owner nearby.

I recall there were lines to use for aligning things in the throttle mechanism. Ran across this post on the Vintage BMW forum which illustrates the point:

https://vintagebmw.org/forum/viewtopic.php?p=82769#p82769

jposig said:

I have 2 of the blue factory shop manuals and the original blue owners manual. I followed the instructions regarding setting up the throttle grip/gears/chain to the cables. There is the proper 2mm
setting on top of the carbs where the cables enter.

I'd love to have it so when the throttle grip is fully forward in the stop position, the motor idles there. This would also fix the dead space from full stop/rearward to actual engagement of the slides.

Click to expand...

Did you mean 2mm or .2mm? 2mm is a lot of free play on a carb cable and when coupled with the normal play in the throttle gears could result in excessive take-up slack at the handgrip. Just a thought…

Best,
DeVern

DeVern -

The 2mm doesn't bother me and I think it's the right value. You need some slack to allow for changing dimensions due to heat, etc. My /7 also has a similar value for slack where the cable enters the ferrule on the carbs.

20774 said:

Including your location in your profile could help if you need a second set of eyes. There might be a vintage BMW owner nearby.

Click to expand...

I'm pretty computer "challenged" and don't know anything about filling out a profile page. I'm located in rural NC on the VA border 8.5 miles from VIR, and work in my shop here on our Farm where we live in the middle of over 1000 acres.

I've seen another Vintage BMW bike like mine on the road in town one day a couple of years ago, but didn't chase the guy down. And I heard there is another guy with a couple of Vintage bikes about 5 miles from me, but I think he checked out.

For sure I'm not afraid of another set of eyes on this issue. I have the marks lined up, the slot is in the correct position, the chain is tight. And yea, 2mm is the factory spec for that clearance where
the cables enter the carbs.

thanks again......

Glad you have some vintage owners in the area. You might check the Anonymous book to see if any listings near you mention vintage bikes.

I'm scratching my head as to what you're saying. Sounds like you're doing everything right in terms of alignment. Something else must be wrong. Is the cable new?

Kurt is right on and 2 mm is not much......If you remember the nickels that used to rattle around in our pockets before debit cards.........Anyway, think of one of them....Not quite 2 mm but close enough.

DennisDarrow said:

Kurt is right on and 2 mm is not much......If you remember the nickels that used to rattle around in our pockets before debit cards.........Anyway, think of one of them....Not quite 2 mm but close enough.

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thanks for the offer. I've been to Road Atlanta a lot and Blue Moon Cycle saved me when I was down there and ruined an exhaust on my R75/5. Sad they are done with BMW parts department.

Cables could be original. However, when I have them removed from the throttle grip housing, I pull each one and the slides move right away and are smooth. Now I know the gears are cut to be progressive and that system also acts as "cruise control".

I'm off to VIR to test a BMW race car today but will be back on this issue tomorrow. Weather has been beautiful and I'm anxious to get back out to ride after about a 3 year lay off due to medical crap.
Getting old is over rated.

I filled out some stuff on the profile area, not sure if I did it right though.

Looks good! Enjoy the track!!

Random thought....is there a "return" spring inside the carb? There's supposed to be a spring at the end of the cable that hooks to the bottom of the slide. It's grayed out in this picture but it is #6:

https://www.realoem.com/bmw/enUS/showparts?id=0211-EUR-04-1958-T50-BMW-R50&diagId=13_0829

'58 Throttle Issue

20774 said:

Random thought....is there a "return" spring inside the carb? There's supposed to be a spring at the end of the cable that hooks to the bottom of the slide. It's grayed out in this picture but it is #6:

https://www.realoem.com/bmw/enUS/showparts?id=0211-EUR-04-1958-T50-BMW-R50&diagId=13_0829

Click to expand...

Please read my original post that I edited with "THE FIX"......

I can't seem to figure out what you changed and what the fix it. Could you post again with specifics as to what you did? That way we have a beginning, middle, and end to the situation!! Thx....

20774 said:

I can't seem to figure out what you changed and what the fix it. Could you post again with specifics as to what you did? That way we have a beginning, middle, and end to the situation!! Thx....

Click to expand...

Facing the rear of the bike, I rotated the gear and then installed the it 1.5 teeth rearward from the marks which took out the slack in the chain, which was there when using the factory timing marks for initial set up.

Make sense?

Thanks for that. It does make sense to over rotate one direction that as things slide into place, it rotates back to where it is supposed to be.