Velocity Governors governors are the simplest. They run on vacuum and mount between the carburetor and the intake manifold. They are compact (usually no more than an inch or so in thickness and only as wide as the carburetor's mounting flange), easily installed, and adjusted with just a screwdriver. These governors just limit the maximum RPM an engine will run and so act as protective devices. Years ago they were commonly found on engines in taxi cab fleets. Today they are found on Chrysler Industrial LH 318 and Ford V8 industrial engines.