1977 BMW R100RS Bing Type 94/40 Carburetor Rebuild-Refinish

This is the fourth set of Bing CV carburetors I’ve completely rebuilt. This is the link to the current work on the 1977 R100RS that uses the Bing 94/40 model of carburetors and specifically the 103-104 series used on the 1977 “CFO” engine version of the R100RS.

The previous rebuilds include the smaller 64/32 series used on the R75 series /5, /6 and /7, and the R90/6 bikes and the larger 94/40 series used on the later R100 model bikes. I documented the procedures of the earlier work in the following write-ups.

As is often the case, I found the o-rings were hard and brittle and in one instance I found two o-rings on the idle fuel jet! The internals were pretty clean so I someone cleaned the carburetors and for some reason added an o-ring instead of replacing it on the idle fuel jet.

I decided to shoot some short videos to demonstrate how I understand the way the Bing CV carburetors work. Each video covers one of the four major functions, or circuits, used in these carburetors. The operation of the model 64 and 94 CV carburetors is the same.

Constant Velocity Circuit Operation

Here is a short video showing how the constant velocity circuit works.

Main + Needle Jet Circuit Operation

Here is a short video showing how these components work in the main+needle jet circuit.

Enriching Circuit Operation

Here is a short video showing how the enriching circuit works.

Idle Circuit Operation

Here is a short video showing how the idle circuit works.

Here are some pictures of the completed carburetors.

Refinished Outside

Refinished Outside

Refinished Inside

Refinished Inside

Refinished Back

Refinished Back

Refinished Front

Refinished Front

Refinished Top with Added Rondel

Refinished Top with Added Rondel

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