fuel level in the carburetor bowl

Mine measures 12.5mm so you are not far off and I doubt that 0.5mm will make a huge difference.

Thank you Kevin, you are among the opinions that I listen to

Thank you so much 

Jacques ( James for you ! )

The floats and the float bracket determine the amount of fuel allowed in the float bowl by opening and closing the float needle valve- Please see the Rotax HMM for float bracket height adjustment https://www.rotax-owner.com/manuals/MMH_912-914_Series_ED1_R6.pdf section 73-00-00 Page 30

If the floats are not "heavy/sinking" and the float bracket is adjusted correctly and is within spec, the level of fuel within the carburetor should be correct. Rotax does not provide information regarding the height of fuel in the float bowl.

Can you provide reasons for you wanting to know this information as it may help with further answers to your question? 

There are 5 engines , in my club , that have been running with Bing Moto BMW R 100 floats for 150 hours over three years

these floats cost 24 € ...

We did not notice any problem with this adaptation.

To adjust this type of float, I need to know the fuel level in the carburetor bowl.

Yes, I know, it is not good to put in anything other than Rotax parts, but after several float problems, I am looking for a way out to have a solution.

Be careful, I don't want to encourage anyone to use this type of float, but after 3 changes, I try.

I know it works (however removing the guides from the old floats)

Anyone who provides you with information regarding the level of fuel in the float bowl would have to make sure their float bracket is adjusted as per the HMM and have floats that are within the proper weight spec. If any of these are "out-of-spec" could provide you with the incorrect fuel level (Just an FYI)

With that said, we have not seen/heard any issues or complaints regarding the newest floats that ROTAX released that have R stamped on the side.