how does a governor work on a small gas engine?

This may have a classic flyball governor, often mounted on the camshaft. At the speeds these engines run, the weights don't need to be very big at all. So, you have a balanced pair of weights on a linkage between two collars on the camshaft. One collar is fixed, the other can slide axially on the shaft as the weights move in and out. There might be a hole in the center of the camshaft that allows a rod to be pushed out by a spring. There are a number of different arrangements of bringing the linear movement of the collar out of the engine. Some have a little shifter fork arrangement, some bring it right out the center of the camshaft, etc. This could be builton the crankshaft as well, but must engines I've seen with mechanical governors hat them on the cam, as it is higher, thereby closer to the carb.
Smaller engines usually have pneumatic governors that work based on air pressure from the flywheel-blower.
Jon

My Kohler 12hp K301S is exactly as you describe. I'm sure Grant's 16 is the same.
Karl

Go to the Kohler engines web site, find the "contact us" link and send them email with the model / serial number info from the engine and ask about owners and service manuals. I did that a few months back for the 10 HP Kohler in my old Deere mower and the next morning had an email from them with links to the full PDF owners and service manuals to download as well as links to the parts site and a note to watch out for part number that may have been superseded more than once... and this is a 32 year old engine (still runs great).

In an aside, I have seen many publications that credit James Watt for inventing the flyball governer. But I have seen good, reputable publications that claim the flyball governer goes back further, and was first used to regulate gates for water wheels. What Watt apparently did was adapt it to steam engine. And then, of course, someone later adapted it to internal combustion engines.

Grant,
Like other posters said, it it is typically a centrifugal with weights or (the only ones I have ever seen) driven by airflow around the engine. From your description, you might have the former type.
Please note that caution is required when repairing governors. If you get it wrong, the engine can run out of control and turn into a small bomb. So far, the best I have been able to figure out is to not bend any of the springs. If there is a secret to it, it is lost on me. Note that I have never actually replaced governor parts; so far, I have found them in good condition, and merely in my way when rebuilding carburetors.
Hopefully someone can enlighten us both on ways to sneak up on it safely.
Bill

A few years back my wife and I visited the Kohler factory in Wisconsin. The factory tour does not include the area in which the engines are made but it was super interesting anyway. To see how bathtubs are cast, toilets moulded and sinks decorated is completly fascinating.
If you are anywhere near Sheybogan WI take th etime to do the factory tour. Reservations are required so plan ahead.
Errol Groff

Do they still sweep-mold plaster molds to slipcast the fixtures? That's the old method, and I've been awed by those sweep-mold craftsmen. It really takes a perfect touch.
-- Ed Huntress

He doesn't. He has the Lt. Governor get it fixed.

If I understand the question the answer is yes. There was a great deal of hand work done on the molds that we saw.
Errol

Most of those shapes in toilets and sinks *look* like they're fully compound in three dimensions, but they're not: they're two-dimensional curves swept through the third dimension, like the shapes on some plywood boats. It's sort of 2-1/2 D. They can be swept with two-dimensional templates, usually guided by a line or a stop that produces the third dimension. If that stop is not a straight line or a circular arc, the result looks like it's 3D-compound.
It requires a lot of practice and finesse to get smooth shapes with that process. We had some of those people here years ago (they were Italians and Hungarians) who worked in the bathroom-fixture manufacturing business in Perth Amboy, NJ. My uncle hired some of them to make sweep molds for industrial insulation covers. It was fun to watch them work.
-- Ed Huntress

Think of governors as servo loops. In the fly ball type, the moveable member consists of balls raised against the force of gravity. Centrifugal force moves the balls. In the air pressure type, the moveable member is an air vane operated against the force of a spring. Air pressure is usu. created by a fan consisting of fins on the flywheel. In both types the moveable members are linked to the throttle of the engine. As engine speed increases or decreases the moveable elements act to vary the throttle position accordingly.
In other types, a weight attached to the side of the flywheel is moved against the force of a spring to vary throttle position. In some types, the weight's position, or the balls position, effects the latching - unlatching of some engine component such as the exhaust valve.
In each type the throttle is connected to the moveable element by appropriate linkage.
Bob Swinney
I have looked at several small gas engines over the years without understanding one basic thing: how does the governor work? I see a lever on a shaft, and on one end of the shaft is typically some kind of spring which applies tension which can be modified to change the set point of the governor. The other end of the lever is usually connected to the throttle.
Clearly what's going on is happening inside the engine itself. Can anyone explain what happens there? FYI the current beastie under consideration is an old Kohler 16 hp one-cylinder 4-stroke enginer.
Grant

In our state the governor would first pick a fight with the legislature to prove it was their fault. The argument would go on so long that it never would get fixed.
Karl

If you are talking about a small air cooled engine (think lawn mower) the governor is probably just a small sheet metal vane pivoted in the airstream from the flywheel fan. A short arm is connects the vane to the carburetor linkage. The faster the engine runs the more air is blown and the more force is applied to the vane. The movement of the vane is opposed by a spring. The spring tends to open the throttle while the vane tends to close it. Depending on the relative force of the spring and the vane the engine will be governed to some specific R PM. Note: These are very rough and ready governors and are not highly accurate.
Higher end engines use some form of fly weight governor, usually in side the crank case which is much superior to the vane type.
Bruce-in-Bangkok (Note:remove underscores from address for reply)

consists of balls the air pressure type, pressure is usu. moveable members are linked moveable elements act to the force of a spring position, effects the If you are talking about anything bigger than a one-lung motor with an "internal" governor hidden in the crankcase, the external flyweight governor is probably driven by a fan belt - and belts can break. And most prime mover engines can accelerate to destruction when the governor fails and the throttle control slams to Full Open.
Any engine running unattended should always have some sort of a secondary rev limiter on it, and even an attended one if it can spin up and grenade faster than you can run there and slap the STOP switch. Either a "velocity governor" between the carburetor and manifold on a spark-ignition motor that cuts the airflow, a rough flyweight system inside a diesel injection pump that cuts the fuel, or a tachometer sensing system that cuts the ignition/fuel/air.
The secondary system doesn't need to be balanced or accurate, since the primary flyweight governor is supposed to do all the precise work. The secondary governor just has to kick in at or near the redline of the engine or the driven equipment (whichever is lower) and avoid a catastrophic failure - hunting and surging while running on the secondary governor will provide an alarm function of sorts.
Had to replace both governors on my PE-95G. The primary was worn out and sloppy enough to not hold a solid 1800 RPM - instead of a clean sealed oil supply, some brilliant person ran the Purolator Junior crankcase oil filter return line through it via the top 'Fill' hole, and rigged an overflow drain from the side 'oil level' plug to the timing cover that more likely kept it overfilled...
And the velocity governor was missing - removed by someone who didn't understand why it was there, ergo it was excess baggage.
-->--

I think that you are letting nomenclature get in the way. A diesel engine has a governor that controls the engine RP M. Full stop!
However, many commercial engines that may, or may not, run unaccompanied have a "shut down system" that senses various abnormal conditions such as low oil pressure, high water temperature or overspeed and shuts the engine down if one of the settings is exceeded. The old 71 series Detroit diesels had one of the best systems with sensors all over the engine connected to a butterfly in the intake. If any sensor was actuated it triggered a solenoid that shut off the air supply to the engine.
Bruce-in-Bangkok (Note:remove underscores from address for reply)

Lots of ways to do engine control, some a lot simpler than others. Basic Briggs governor is a fan on the flywheel blowing on a vane. Other end of the vane is hooked to the carb butterfly with a wire linkage and a spring. Engine shroud covers all but the outer end of the vane with the spring on it. Cheap, simple and it works for lawnmowers. For tighter speed regulation you start getting into centrifugal weights and linkages. Thousands of designs for that. Get the tech manual for the engine and see what you've got.
Stan

Some newer engines, e.g. B&S industrial in that power range, are going to electronic speed control: sense speed from magneto, solenoid-controlled throttle.
They'll get it right eventually.
Meanwhile, possibly of passing interest re background content: