Quite a few stationary and old school truck diesels run a throttle butterly . They act as a cheap engine governor for fixed speed running and also reduce the overall noise from the inlet . Open the throttle and the rack in the pump is pulled back by a spring to give max fuel , close the throttle ( vacuum ) and the diaphram will pull the rack back to the fixed speed. With these engines its very hard to stall them because as the engine revs drop so does the vacuum and that in turn opens the pump which resists stall. The only way you are going to reduce the smoke on snap throttle response is to suppress the vacuum signal because as soon as you dump the vacuum you are on max fuel. Some road going early diesels ( merc and Bmc ) ran a throttle butterfly in the inlet to get vacuum for brakes, these used ordinary injector pumps . I know all this shite because I am old.
Bob