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The Plunger
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VBMWMO #8356
Joined: 09/03/2012
Posts: 184

Hello, all. I've been meticulously going through my carbs and have come to learn something I didn't know regarding the air mixture screw and it's evolution over what appears to be a very short time frame. This may bore some of you, but for you OCD types, read on.
Early T117 body Bing carburetors circa 1951-53 had a simple, solid, air mixture screw with lock nut. In addition, there was the "schutzschraube" (33) literally, "protection screw" mounted on the small slanted pad below the intake. It's function was to let air into the carb. The earliest air mixture screw (11), seated itself into a threaded brass unit, "Leerlaufluftduse" (44) utilizing the same threads as the air mixture screw. Later, part (44) was deleted and the mixture screw was seated into the carb body pot metal from there onward. My manual states part (44) was used on R51/3's up to #526709 and R67/2's up to 611449, placing them into the late months of 1951 production. I guess they figured the pot metal was good enough as long as the screw wasn't overtightened.
The next change would be to the air mixture screw to it's final form we all know and love. That is, the longer, vented screw with the collar and cap which negated the job of the Schutzschraube which port was simply plugged on castings thereafter. My manuals, being early, do not state when the schutzschraube was deleted but I'd guess late 1952 or very early 1953. The Barrington book(page 251-252) says it was gone with R51/3 #528760 and R67/2 612861.
I purchased a pair of rebuilt carbs sight unseen from Germany with the schutzschrauben, which I favored, only to find they had the newer style air mixture screws and collars installed. Upon removing the airmixture screws I found that one carb has the (44) and the other does not. Are the BMW concours gods going to know? Doubt it.
So, I need to find a pair of old style air mixture screws. Anyone?

Brian

  • parts_11_and_13_luftregulierschraube_and_mutter.jpg
  • part_33_schutzschraube.jpg
  • part_44_leerlaufluftduse.jpg
  • bing_carb_crop084.jpg
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Brian
'52 R67/2, '53 R51/3

808Airhead
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VBMWMO #7677
Joined: 08/05/2009
Posts: 1010
Vech stocks the solid mixture

Vech stocks the solid mixture screws and lock nuts. I have one carb that runs richer than the other no matter what adjustment I do,I a going to see if it is missing #44. Thanks for this!

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Thomas M.
R69s - R60/2 - R67/2 - R51/3

The Plunger
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Joined: 09/03/2012
Posts: 184
Yup, Richard had to work to

Yup, Richard had to work to find them. They are used in R26 & R27 and R51/2 but not listed as parts for R51/3 or R67/2.

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Brian
'52 R67/2, '53 R51/3

jambo
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VBMWMO #9208
Long Island
Joined: 11/23/2016
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Benefits of either?

Brian,

This is very interesting. I purchased 2 x R27 carbs for my R27 restoration. One came with the air screw as in parts 11 and 13 and the other came with the new style with a collar. I do not believe the inside of the older one that had parts 11/13 had the part 44 inside (I am usually quite good at noticing those things) but now I will need to check that to make sure.

I wonder, whats the advantage or disadvantage to running the older setup versus the newer style with a collar?

Thanks for bringing this up, I figured someone just put the wrong part in the older carb!!

James

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James W.
1966 R50/2, 1963 R27 and 2018 R1200GS

The Plunger
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Joined: 09/03/2012
Posts: 184
James, The newer style air

James,
The newer style air screw with collar and cap will work in place of the old, you just have to delete the schutzschraube by plugging it. Coversely, if you don't have the schutzschraube, you better have the newer air mixture screw setup. The schutzschraube is the air inlet for idle but when Bing figured out that a hollow air screw could do the job it made the schutzschraube obsolete. One less machining step and less parts! For performance and easier maintenance I would go with the newer setup but I'm a stickler for period correctness so I'm using the originals.

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Brian
'52 R67/2, '53 R51/3

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