Bing Type 53 Carb Question

[RPGR90s]

I'm helping a buddy with the stock Bing Type 53 carbs on his '72 R50/5. We're rebuilding the carbs and I see there is an accelerator pump as part of the main jet/mixing tube assy.

I'm curious how this actually works so I can verify it's operation when re-assembled. I'm very familiar with Dellorto PHM carbs (R90s) and their accelerator pumps, as they use a specific jet to squirt fuel when the throttle is opened, via a small lever that slides on the carburetor slide. So its easy to verify a stream of fuel being squirted when the slides are raised.

But the Bing's have a much different setup, using a small spring loaded wafer/disc inside of the mixing tube.

Thanks for any guidance/explanation.
RPGR90s

 

[69ZEFF65]

I have no idea how it works but I just did a deep dive into one of my R 50/5 carbs 113 & 114 to address a stumble on acceleration. I replaced the coil spring and those little tiny wafers in the mixing tube and the stumble was gone. Eruomotorelectrics (maybe misspelled) had them for a couple bucks and they that took care of the stumble.

 

[AntonLargiader]

When the needle drops, it pushes the plunger down and fuel fills the space on top of the plunger. When the throttle is opened and the needle lifts, that fuel is squirted up into the air stream.

The wafer is part of the check valve that allows that area to fill but not drain back downward.

 

[RPGR90s]

When the needle drops, it pushes the plunger down and fuel fills the space on top of the plunger. When the throttle is opened and the needle lifts, that fuel is squirted up into the air stream.

The wafer is part of the check valve that allows that area to fill but not drain back downward.

Thanks very much Anton. I wasn't certain if the needle was involved, but that makes sense now. So I'm assuming that if I remove the air cleaner tubes and twist the throttle, that I would see the fuel being sprayed via the needle jet tube?

 

[AntonLargiader]

Yes, you can. Just verified. You can also hear it.

 

[RPGR90s]

So I was able to fine tune the carbs after my buddy came over with his R50/5. And yes, when the slides are raised, there is a noticeable spray of fuel coming from just below the needle up into the venturi of the carburetor. The flat spot off of idle is gone and the bike runs as near perfect as you could expect.

I never quite knew how these worked as I mostly work on Bing CV's and Dellorto's, so thanks for educating me on these fine little carburetors.

 

[69ZEFF65]

Thank you for the explanation Anton and thank you for the follow up RPG90s.

 

[RPGR90s]

Thank you for the explanation Anton and thank you for the follow up RPG90s.

Absolutely.
The symptoms were similar to yours. A stumble just off idle. I remembered something about these carbs having an accelerator pump, so that peaked my interest. The Dellorto's on my R90s have a very specific jet stream of fuel that squirts like a modern automotive carburetor, but the Bing has more of a "deposit" of fuel that comes up through the slide needle as the slide is raised. Different, but the effect is the same. Very clever engineering IMHO and it solved the problem.