The BMW R12 was fitted with two different types of Carburetors during its production run. It was the SUM and the AMAL carbs or in German, “ Vergaser”. For the Tour version which was dual carbs (Zivil) we had the AMAL Typ 6/406 SP and the 6/407 SP. As you can see below the photos of this carb. When you had the only the single carb it was the SUM CK 3/500F. Both carbs work great and are reliable. You see many Wehrmacht motorcycles equipped with the SUM.
Below are technical drawings of the SUM CK 3/500F Carburetor
Above is the metal ID plate often seen on the BMW R12 SUM carb. This plate says at the top for 1940 for high octane 74. The next line says Muster 769 Werk Nr. The last line is all the needle s that are on the float. Lfd stands for Leerlaufdüse it is the idle jet at 35. Ud stands for Übergangsdüse it is the middle jet and it is a 65. The last jet is Hd and this is the Hauptdüse at 70.
Below are photos of the AMAL dual carbs for the R12 civil models.