The DU6 carburetter

These dual choke carburetters of It in. diameter throttle bore were used almost exclusively on the Coventry Climax 11/2 litre twin cam engines. New units are not now available.

Whilst they work on the basic S.U. principle they have an additional full throttle - diaphragm operated weakening device. It was necessary to introduce this weakener to overcome excessive mixture spread between full throttle and part throttle conditions. Without this device it was found that correct part throttle tuning produced an over-rich condition at full throttle, and conversely, correct full throttle tuning resulted in an over-weak mixture at part throttle.

One other feature on these instruments was the positioning of the float chamber between the two chokes of the carburetter. This necessitated the use of a narrow rectangular doped cork float, which is satisfactory in petrol but cannot be used with methanol blends.