Here are the pictures of the vacuum test of the governor housing. The text is also for the uninitiated.
How to test the pneumatic governor for leakage:
Do this test with the engine off. It can be done with or without removing the cable to the starter knob.
Here you see the pneumatic governor or the diesel pump. It is to the right of the red cap. The hose provides vacuum to the governor housing, the vacuum is produced by means of a venturi in the air intake. The housing must be air leak free, otherwise the governor cannot work properly and/or the engine will use more fuel.
Remove the air hose with a 17 mm wrench
Put the lever of the pump in the stop position, i.e. to the left (if you haven't removed the cable, put starter knob in the stop position, i.e. push in).
Now, while keeping the lever in the stop position, connect a vacuum gauge.
Release the lever to the normal position, the vacuum gauge should now indicate a small vacuum: 70-90 mbar or about 4 in Hg
This vacuum should stay constant.
If you haven't got a vacuum gauge, an easier test is possible.
Instead of connecting a vacuum gauge, put your thumb on the opening (while keeping the lever in the stop position:
Release the lever and keep your thumb on the opening
When you take off your thumb, you should hear a click. If you keep your thumb longer on the opening, you can check how long the vacuum stays.