R51/3 is leaking fuel from the idle mix screw

Begonnen von Michael Steinmann, 17 April 2021, 19:10:34

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Michael Steinmann

Hi all. The carb is a Bing 1/24/159, was bought new 5 years ago by p/o.
It went through a cleaning process by me, as the bike stood for some years BUT I did not touched this mix screw and left it in place. 
The cover plunger/needle valve system was checked and is ok, also the float.
Still, I get a massive fuel leaking from this mix screw on the carb's side as soon as I open the tank petrol tap.
I would be thankful if you guys could give me a tip of where to search, because I really don't know how to proceed.
It also occurs without the throttle cable attached.
Thank you very much in advance -
Micha Steinmann


Hello Micha,

may be that the "needle" inside the fload is not in the correct position - another possibility - the needle is hold tight in the lower "pinhole" of the housing because of deposits which are built up in the "off season"

Best regards


Michael Steinmann

Thanks Bernd.
The needle inside the float is turning freely and was not touched while cleaning procedure. It is in its original position.
BTW - I can't see any grooves on it. It do has this small washer with the 2 wires soldered to the top of the float.
In fact, float was just tested to be water tight and then put aside.
That well that the needle is entering was soaked with carb cleaner and even with vinegar, so I assume all is clean there.


Maybe you can make following tests
Check the fload-position of the both carbs by opening the petrol-tap. Close petrol cap and remove the lid of the float-chamber. Measure the positions of the floats - are both positions equal?
Then change the floats from the left to the right and the right one to the left carb.
Close lids and open the tap - what happens?



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