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My left Bing on the r100t is leaking fuel ever so slightly out of the overflow tube, and I presume this to mean that the bing's float bowl is being overfilled, which makes me think the Float arms need adjusting, or something is otherwise amiss with the needle?

If I understand the anatomy of these bings well enough, the float arm lifts based on the level of the fuel in the bowl, and the float arms adjust a needle that presses against the fuel intake line once the "full" point is raised.

Is there something simple I can do to check what part is wrong? If I'm gonna end up having to open the float bowl at all, is it imperative to replace the float bowl seal/gasket? Should I just go and do a full "rebuild" of the carbs if I have to get in there at all?

I don't know anything about the past work on the carbs, such as when it was last tuned, rebuilt, or any other types of service, but it's very clearly leaking due to being overfilled.

Thoughts and recommendations?

The first thing I would check is to make sure there isn't a bit of debris keeping the needle and seat from closing properly. What I have done in past is the remove fuel line from where it couples with the cross over and insert a HAND PUMP in line and blow the crap loose from the seat, sometimes that works rather than taking the carb off.
When I have adjust float levels, horizontal is a good place to start, but when I experience starvation at that level, I just fill each bowl as normal from the tank, close petcock, remove bowl and measure the amount a fuel in the bowl, I try to get each float about the same with that measurement.

jagarra wrote: ↑Fri May 14, 2021 5:05 pm The first thing I would check is to make sure there isn't a bit of debris keeping the needle and seat from closing properly. What I have done in past is the remove fuel line from where it couples with the cross over and insert a HAND PUMP in line and blow the crap loose from the seat, sometimes that works rather than taking the carb off.
When I have adjust float levels, horizontal is a good place to start, but when I experience starvation at that level, I just fill each bowl as normal from the tank, close petcock, remove bowl and measure the amount a fuel in the bowl, I try to get each float about the same with that measurement.

If I'm doing simple measurements like this, where removing the bowl is necessary, do I need to be worrying about the gasket for the float bowl? My original concern about the leak was that it was the gasket that was bad, causing the leak, up until I finally found where the leak was actually happening from.

Be very careful with those gaskets. They are small and thin. Be sure that the bowl fits into the slot with the gasket in place before snapping the bale to hold the bowl on.

Typically, the fuel level in the bowl is less than the depth of the bowl, so the gasket isn't necessarily the problem. If the fuel gets that high in the bowl, then the float didn't shut the flow off. And then if it is that high AND it leaks then it could be the gasket or it could just be the fuel going out the overflow tube.

Kurt in S.A.

Kurt in S.A. wrote: ↑Fri May 14, 2021 5:53 pm Be very careful with those gaskets. They are small and thin. Be sure that the bowl fits into the slot with the gasket in place before snapping the bale to hold the bowl on.

Typically, the fuel level in the bowl is less than the depth of the bowl, so the gasket isn't necessarily the problem. If the fuel gets that high in the bowl, then the float didn't shut the flow off. And then if it is that high AND it leaks then it could be the gasket or it could just be the fuel going out the overflow tube.

Kurt in S.A.

I've already confirmed that the "leak" is *solely* coming from the overflow tube to the best of my abilities to isolate it. I am pretty sure it is something pretty simple, as Occam's Razer tends to agree.

What is the simplest thing that could be preventing the flow from the tank to stop in this situation? Bent float arms? worn needle?

SteveD wrote: ↑Fri May 14, 2021 10:26 pm Taps off. Bowl off. Collection device under the carb. Taps on. Flush the petrol thru whilst jiggling the float up and down. Reassemble. Test.
Hopefully that flushes some junk caught on the seat which might be stopping the needle from seating and closing the flow.

You could use a pencil and lightly lap the seat whilst in there.

If that doesn't work.
Bike on centre stand. Bowl off. Tap on just enough for flow. Raise the float and see at what point it causes the flow to stop. It should be when the float is parallel to the carb body.


If it doesn't do what it should, then you'll need to adjust the float height.

Next step would be to measure float weight. Old and heavy might need replacement.

Thank you for the write-up! I'll give this a try and see if I can't spot an issue anywhere.

I'll have to give this a try when I can be on level ground. I realized probably too late that the only time I've tested the "leak" was on pavement that had a somewhat significant angle to it (our parking spot at our complex). Might have been *just* enough for a normal-working float to experience some "overflow" in the bowl, causing the float to lower just enough to let more in...etc. I don't know for sure if this is true or not, but I'd like to test the float overflow on flat ground, as well. Just to make sure.

Once confirmed that it is actually leaking, I'll give your steps a try and go from there.

I just ordered gaskets for my R100T from Max BMW. $3.58 each. Free shipping! Got them in a few days with a bag of M@Ms in the box. Does not hurt to have them in stock.

No, you do not have to change them each time. But that does not hurt either. I grease them to keep them in place before installation.

daz wrote: ↑Sat May 15, 2021 7:13 am I just ordered gaskets for my R100T from Max BMW. $3.58 each. Free shipping! Got them in a few days with a bag of M@Ms in the box. Does not hurt to have them in stock.

No, you do not have to change them each time. But that does not hurt either. I grease them to keep them in place before installation.

daz beat me to replacing the gaskets, especially on an old bike new to you.

I don't think anyone has mentioned hardening of the float needle seal. Red, I believe. Again, not real expensive.
Make two orders and get twice the M&Ms!

Also, the floats themselves are considered to be a "wear" item. Requiring replacement if/when they begin to absorb fuel.

Snowbum gives the details here near in the top of the page, without excessive verbage:

https://bmwmotorcycletech.info/bing-floats.htm