Some of us when we are looking at an engine we get scared. We see springs and levers and linkages coming out from who knows where; we know they’re important for the operation of the engine.
As an example I was doing a little wood splitting this weekend and if it wasn’t for the governor on the engine things would have been a lot worse or different. The engine would have been either not delivering power when I needed it or would’ve been running out of gas constantly and the engine would have been screaming the whole time. Then to make matters worse the engine itself probably would have overheated and then rendered useless at the end of the day.
Governors are important for regulating speed on engines especially on engines such as lawnmowers, log splitters, generators, water pumps: any engine that requires speed regulation for its operation. It might not be readily apparent why you would need the speed regulated so let’s go into that for a few seconds.
An engine has a power band to it. A power band is the range of power that an engine will give out from low RPMs to high RPMs. When an engine is given a horsepower rating it typically is at the top of the power band. For example an engine will be given a rating of 5 hp at 3600 RPMs. Well below 3600 RPMs the motor will only have three and half horsepower at 1200 RPMs. The full brunt of 5 hp will only come at 3600 rpm. The whole idea is to have the horsepower available when you need it. If the engine were giving out 5 hp all the time then it would mean that the engine will be racing and roaring at 3600 RPMs. When the load hits the engine the engine will slow down and you’ll actually have less than 5 hp and may require more.
When a machine is designed, for example the wood splitter, the range of RPM that the engine is actually running at is probably more around 2000 RPMs. When the engine is freewheeling at 2000 RPMs the throttle is not open and fully. It might be an eighth open. When I log is put in the log splitter and is being required to be split then the engine will start to lug down. In order for the engine to maintain the 2000 RPMs that it was at already, the throttle opens up more automatically. Otherwise, the engine will stall or quit at the 2000 RPMs with the throttle just being open an eighth.
The way the throttle automatically opens is by the governor mechanism. This article is going to talk about how the governor mechanism actually operates.
To understand how the governor operates we need to understand the variables that are in the system. First of all the engine is spinning and secondly the rate at which it spins is regulated by the throttle. There has to be a relationship between the throttle opening and the RPMs of the engine. The governor is the mechanism for relating the two.
There are actually two different types of governors on lawnmowers and small engines and they are:
Wind vane governor
centripetal force governor
The wind vane governor uses the air coming off of a flywheel cooling fins. The faster the engine runs the harder the air will blow off of the flywheel fins. The relationship of the wind pressure off of the blower on the flywheel is related to the square of the RPM. The mechanism is quite simple actually and has a simple spring connected up to the wind vane. The spring by its nature is very loose and has a low spring rate. Typically the wind vane governor is used only on lawnmowers.
The centripetal force governor is used on 80% of small engines. Inside the engine is a camshaft. The camshaft has more teeth on it so another gear is able to be driven off of the camshaft. The driven gear has two weights mounted to it. The weights turn on hinges and flying out when the gear is spun. As the weight is spinning out there is a lever on the base of the weight which forces up a driver. This driver can move a quarter of an inch. This movement of the driver is then relayed to the lever arm which goes outside of the crank case. The governor lever arm is mounted to this lever arm. From the governor lever arm is a linkage that mounts directly to the throttle on the carburetor. Additionally a spring is mounted onto the lever arm and has an adjustment typically.
Centrifugal force is related to the square of the RPM as well. So as the RPMs of the engine increases the force that comes off of the flinging out weights increases.
So the way the engine and governor works is as RPM increases the linkage pulls back on the throttle causing it to shut.
There are different modes of the governor:
In order to understand or troubleshoot the governor it’s easier to understand the different modes that the governor will leave the engine in when it’s in different states. The different modes are:
The rest position of the engine is when the engine is off. In this mode the governor will put the throttle in the full open position typically. The reason for this is that when you want to start your engine you need to have more than no throttle but, full throttle. So when the engine is at rest the governor will be pulled over by the spring so that the throttle is at full open. The way the throttle is adjusted in speed is that the force coming off of the spring needs to increase. In other words something has to pull on the spring, and in doing so it causes the governor arm to pull the throttle over to full open, or be open more.
In idle mode the engine is running and is in its lowest position. Typically a in this position there is little spring force being put upon the governor. So what occurs is that very little amount of centripetal force off of the governor weights is required to make the throttle shut. The natural action of the governor is to cause it to close the throttle. When the weights fling out it causes the actuator to pull the throttle shut. So in the idle position very little resistance to the governor is being provided so the prominent effect is that the governor overrides and closes the throttle.
Mid-throttle is where the engine is running in its natural operating speed. In this operation the governor causes the throttle to move up and down but maintained a constant speed. If there is any governor adjustment issues typically the governor will override cause engine shut down or if there is not enough governor adjustment the engine will tend to go the full throttle. One of the common symptoms of a carburetor problem is that the governor will cause the engine to hunt. Hunting is when the engine is going up and down and up and down in RPMs. The primary cause for this is that the jets in the carburetor become clogged, especially from sitting over the winter months or there is a very old carburetor that needs adjustment in the jet area.
In full throttle typically there’s little left in the throttle adjustment. Meaning there is no more throttle opening left. Full throttle is accomplished, when the engine is sitting at rest as we discussed before. The governor will cause the engine to go to full throttle automatically when there is no RPMs. Full throttle can be accomplished when the spring overrides the governor. Typically this is very difficult to do. There is almost in some cases 10 pounds of force being exerted by the central couple force of the governor system and can override a hand operation of the throttle. But in general, the full throttle mode is accomplished when the engine is under full load, such as lugging through a log, the governor will cause the throttle to go the full open. The purpose for the throttle going to full open is to help the engine get back up to the RPM that it needs to be at such as 2000 RPMs.
Troubleshooting Throttle Governor Systems
To troubleshoot a throttle/governor system the understanding of the four modes is needed. Typically what occurs is that someone has taken an engine apart and they don’t know how to put it back together. Usually what occurs is that somebody has taken the governor mechanism apart and has mistakenly taken the Springs off and forgotten where they should have been. So what they are stuck with is a puzzle of sorts trying to get the engine back together and actually to operate properly. And so the main question is how in the world was a governor set up in the first place?
First of all if you taken in engine apart always make sure that you take a picture or at least have the understanding of governors work before you fully take the carburetor system of apart.
Typically what I will do is I will take the linkage off of the governor and leave most of the other parts on the governor alone. If I need to take the carburetor often engine I will remove throttle linkage only and leave the governor parts alone. Another problem that can occur is that the linkage itself can get lost and so the problem that you will run into is that you don’t have a linkage to replace it with. The linkage has been set from the factory at the correct length which is matched up to that governor mechanism, so again it is best to understand how the governor actually operates, especially at idle. You can take advantage of the idle mode by understanding that the carburetor will be a full throttle when the engine is sitting at rest.
What you do is take a piece of bailing wire which is about .09 inches in diameter or .085 inches in diameter and form it up using pliers so that it mimics the linkage that used to exist. Use of needle nose pliers is best when forming throttle wires. You may have to drill hole in the throttle plate on the carburetor to accommodate the wire or that you’re using. (Be sure to not allow the hole to be too large. Addition of slop in the linkage is devastating to governor performance.) With the engine being at full throttle and the governor in the full throttle position as well set the new wire system together based on these links.
I had a similar problem this winter with my snowblower because the throttle linkage itself had become rusted and disappeared. I had to reconstruct a new throttle wire using this method.
Adjustment of the governor mechanism is where the spring is placed and how much the spring polls on the governor mechanism. It can be difficult to predict what the spring rate was to begin with on an engine especially if you’ve lost the governor spring when the engine was taken apart. But sometimes you can match up off the shelf Springs by pairing up either two together or one. It is best to not futs with the governor spring rates but to find or purchase the correct part if there’s a problem with the governor anyway.
The adjustment of the governor is based on different holes in the throttle arm. The higher you are up on the throttle arm the more force to the governor has to put forth. So in plain English: the higher the spring is upon the throttle arm the faster the engine will go. The lower the spring is on the lever arm the slower the engine will go.
The reason why the engine will go faster when the spring is mounted higher is that the natural inclination of the governor is to close the throttle and it will take more force for it to close the throttle therefore the engine will go faster. The spring wants to make the throttle open that’s what it’s for. The spring is designed to cause the throttle to open up so the more of the spring is pulled on the more throttle opens in the faster the engine goes.
So when the throttle mechanism is adjusted on the engine what effectively happens is the spring is pulled on. Or the length distance between the spring and the governor is increased. Typically this is accomplished using a crank or lever arm. The lever being in the forward position will cause the spring to be closer to the governor as the lever is moved the spring will pull harder on the governor causing the engine to go faster.
So the real big variable that affects the governor system the most is the spring. The second variable is where you place the spring. Like I said before the spring rate should not be played with, use only the manufacturers designed spring. Positioning of the spring at different places on the governor affects how the engine will operate. So if you want younger riders for example to ride to go kart, but you don’t want to go so fast the spring can be adjusted on the governor and cause the engine to only go slow.
So To Recap:
A governor is a control system designed to keep the engine from over-reving and to provide the proper amount of power when it is needed especially on yard equipment. Governors are useful for go carts in that they can keep the go kart from going too fast. You can regulate the speed of the go cart effectively using a governor system.