Is it an early or late B275? Early has a butterfly valve in the air-intake pipe that can get stuck open. Mine got jammed closed once with mud-wasps.
Early BD-144 has a CAV in-line pump box with four injector pumps riding on a camshaft and an air-governor like a old Ford Major uses. Governor hooks to linkage to a butterfly air-valve flapper in the air-intake pipe.
Later BD-144 has a CAV rotary-distributor pump with an internal centrifugal governor.