PER Notebook

Probably the most important part of your engine, at least to the life of it, is the engine governor. Without a way of controlling engine speed, the engine would destroy itself in short order. Never overspeed an engine, especially without a load attached to it, even for a short time. I recently received a Honda gen-set for repair in which the governor had failed and the centrifugal force of overspeeding blew the magneto magnet into 100's of little pieces. So, you can see, overspeeding is something that needs to be taken care of immediately, because it can be a real hazard with metal coming loose at high speed.

So, how does a governor work? Most governors used on modern engines are known as "mechanical governors". In other words they are mechanically linked to the engine crankshaft and use crankshaft rotation speed as a drive force for the governor. Some drive off the camshaft, but the camshaft drives off the crankshaft. The governor usually consists of a gear and fly weights pushing against a spindle and shaft. This transfers a rotation motion into a back and forth motion which can open and close the carburetor throttle. The governor shaft is connected to the carburetor by an arm and linkage. A governor spring is attached to a hole in the arm and gives a counter resistance to the thrust put against the governor spindle by the rotating weights. It is the calibration of this spring that makes everything come out right to maintain a 3600 rpm speed. On variable speed engines, a control cable is connected to this spring to control the engine rpm's by varying the spring tension. All in all, it's a pretty simple device and for the most part very dependable.

So, why doesn't it work right? Most governor complaints fall into two categories:

Before trying to solve either of these problems, you should do an inspection of the governor linkage and spring. Make sure everything is operating freely and the spring is not damaged or stretched. Also, check the governor static adjustment to see that all free play has been removed between the spindle and carburetor. The best way to do this is to move the throttle from idle to full open and note the way the governor shaft moves. If it goes clockwise, then loosen the clamp screw and with the throttle wide open turn the shaft all the way clockwise and re-tighten the nut. Make sure the throttle moves from idle to full open freely after making the adjustment. Your governor setup may look different then the picture, so refer to the engine repair manual for exact adustment procedures.

After making the above checks, restart the engine and see if the governor now operates correctly. With the engine at idle, move the governor lever with your finger to open the throttle and it should push the arm back toward idle if working properly. One way to do this test is with the governor spring removed. If it still over speeds or has no push toward idle, you probably will need to have the internal parts checked inside the motor or recheck the static adjustment. This is not a job for everyone, so see your local repair shop.

The other problem that often occurs is governor hunting or surging up and down. Many times this is not the problem of the governor, but a partially plugged carburetor, especially a plugged idle circuit or worn linkage. If you can rule out these causes and have checked the adjustments I talked about above, then you may have a governor that is set too sensitive. In other words it reacts too quickly and over compensates for the speed. Many governor arms have several holes in the arm to change sensitivity. By moving the governor spring to a hole further away from the governor shaft you will make it less sensitive. Before playing with this, check the repair manual for the engine you have and see if it has a way of adjusting sensitivity. Sometimes you have to change governor springs, etc.

One last thing on governors. Many of the smaller lawnmowers used what is called an "air vane governor". This type of system uses the air flowing through the engine to operate a vane back and forth against a spring, just like the mechanical governor does. The big problem here is debris in the system blocking air flow. When this happens the engine will overspeed. So, with an air vane system it is very important to keep the cooling fins clean so the proper amount of air can move through the engine. The governor spring is precisely calibrated for an engine that has full air flow going through it.

I hope this information has been helpful and if I think of something I missed about governors, I'll include it here. The governor is a very important system on your engine that often gets overlooked - Bruce Perrault