How do you disable the governor on a 16 hp onan?

First off, why do you want to do it? The governor serves two purposes, depending on the application. On generators it maintains the proper engine speed for the desired voltage output. On a tractor it allows the operator to set the engine speed to match the task at hand, such as running p.t.o. driven machines or maintaining a steady ground speed for mowing. On equipment where the operator adjusts the engine speed the governor also prevents over-speed which can cause the engine to self destruct.

Disabling the governor is simple. Just disconnect the governor linkage at the carburetor and connect your throttle control directly. I'd suggest leaving the governor connected, though. It's there for a very good reason.