What is the leaning procedure for the Stromberg Carburetor?
A30: This carb “automatically” leans due to the methods employed internally. Saving 10% of your fuel in a 4GPH aircraft could be very expensive when you start burning metal parts. The mixture control on the Stromberg carburetors does not work in the same fashion that more recent mixture controls work, i.e. later ones completely cut off fuel flow at idle in the mixture full lean position via a mechanical equivalent to a shut off valve. The Stromberg carbs are fitted with a method of putting slight vacuum on top of the float bowl in the carb which has the effect of reducing the fuel air ratio (leaning) when the engine is running at cruise power. It has minimal effect at idle and is not intended to shut down the engine. This back suction mixture control is not highly predictable and should not be used without an EGT. The concept of never leaning below 5000 (or 6000) feet is a corruption of the intent of the comment and generally applicable to the later Marvel Schebler carbs. The original
