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Beemer100
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Germany
Joined: 05/15/2018
Posts: 28

here we go, first help needed ...

Its about my R69S (w Hollandia) which I use in Canada. It is all stock (26/91-91 carbs with large filter). Original magneto. The bike was restored by Barrington a while ago and has now roughly 1000 miles on the new engine.

The bike starts nicely (2nd kick after winter hibernation) and also 1st/2nd kick when hot. S shows in window at idle and goes up to stable F as from 2800 revs (bike is equiped with a tach). Now, what I see is when I rev the engine higher, starting at 6200, the F moves out of the window (to the top) which would mean that the bikes fires earlier than the 39 degrees at full power (42HP/7000). Can this be right?

The result is that after roughly 30miles the bikes gets horribly hot (feeling, compared to all my other airheads since I don't have a temp gauge), in particular on the right side. When getting to a junction the revs return very slowly to idle once I shut the throttle. After shutting off the ignition I hear 1 or 2 metallic knocks in the end.

I am running the carbs with 135 main jet and the idle jet is a 35. Needle hangs in 3 position (which would be too fat according to the book). The plugs are pretty white. Carb cleaner test shows no leaks.

Any help or direction is highly appreciated. I will get there (Canada) in fall and I would love to ride this biest rather than spending another couple of weeks sitting in front of it not knowing how to get it run properly

best regards
Klaus

Daves79x
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VBMWMO #9030
Joined: 08/09/2015
Posts: 304
Off The Top

Without actually looking, I think you are actually running too far advanced at higher revs. You likely have a broken advance stop spring or a broken weight spring. Easy to check and should be done before much more running. As I said, this is just off the top of my head without thinking it through too much.

Dave

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Dave

schrader7032
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VBMWMO #7032
San Antonio, TX
Joined: 10/27/2006
Posts: 6540
Dave beat me to the punch!

Dave beat me to the punch! The F-mark should never leave the window...too high of an advance can hole a piston. You didn't say what year your R69S is. There were two different advance stop mechanisms shown on Duane's page:

http://w6rec.com/duane/bmw/advance/index.htm

PS...don't click on the link below the images of the advance unit...leads to a malware site...I'll let Duane know.

The second version is better. If you have the second version, there is a feature that can make it even better. It's anecdotally called the Caro stop screw. It replaces the curved spring with a screw that can dial in the amount of advance. That and other things are covered in this thread:

http://vintagebmw.org/v7/node/12639

I thought that Vech sold them but didn't see it on his online store.

Looks something like this:

https://www.flickr.com/photos/roundel/16498718/in/photostream/lightbox/

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Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

Beemer100
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Germany
Joined: 05/15/2018
Posts: 28
thanks Guys, it is the latest

thanks Guys,

it is the latest version (U-shaped spring). Question is, why did they put there a spring in the first place if ignition should not be advanced before 39 degrees?
Funny is, I tried the same procedure with my R50/2. Same thing: S @ idle, F @ around 2.500 (don't have a rev counter on that bike, though) but when I rev it higher, The F mark disappears. Now, the R50/2 obviously doesn't get to that high revs and for that reason the engine runs very nice at very nice temps.

What idle jet do you guys run in your R69S? Is it a 35 or a 40?

thanks and best regards
Klaus

schrader7032
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VBMWMO #7032
San Antonio, TX
Joined: 10/27/2006
Posts: 6540
The spring actually serves

The spring actually serves two purposes. It's a crude advance curve device...it slows the rate of advance as the advance peg pushes against the spring. Then at some point, the spring is supposed to completely resist the further movement of the peg and weights. Could be that your springs are weakish and they allow some deflection past the full advance point. That's where the stop screw can be helpful.

According to the Bing manual, the 26/91-92 carbs take 35 idle jets. Further info here:

https://w6rec.com/bing-carb-specs/page1-7/

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Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

Beemer100
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Germany
Joined: 05/15/2018
Posts: 28
Thanks Kurt I brought the adv

Thanks Kurt

I brought the adv mech and the carbs back to Germany so I will check them according to the info I got here. Hope I will be successful in fall when I return to Quebec.

I think I read that in NA these idle jets were changed to 40 to adjust for the gazoline. Not sure where I read this, though. I was thinking the metal knocking after turning off the ignition would come from a too lean idle mixture ... also the fact that the revs don't react spontaneous when I close the throttle (@ hot engine).

best regards
Klaus

schrader7032
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VBMWMO #7032
San Antonio, TX
Joined: 10/27/2006
Posts: 6540
I've not heard of any NA

I've not heard of any NA versus Germany adjustments. Basically, you start with the Bing manual numbers and evaluate from there. Nothing cast in stone...just how does the bike perform.

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Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

Beemer100
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Germany
Joined: 05/15/2018
Posts: 28
Thanks for your help and

Thanks for your help and advice,

I will let you know in fall how the biest is behaving

best regards
Klaus

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