If your lawnmower’s engine is over and under speeding while in operation, it could easily be an issue with the governor spring. Something as simple as a two or three-dollar spring can cause problems such as a lawn mower engine surging and over-revving. Not only do these types of problems make mowing a real struggle, but they can also cause extensive damage to your mower. So, let’s take a closer look at lawnmower governors and see how they work, the common symptoms when they’re faulty, and how to replace a governor spring.
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Symptoms of a Bad Lawn Mower Governor Spring (Overview)
When a lawn mower governor spring is bad, the engine can no longer control the engine speed under varying loads. The following are four common symptoms of a faulty lawn mower governor spring:
- Problems Starting Your Lawn Mower
- RPM Fluctuating and Surging Engine
- Engine Bogging Down & Loss of Power
- Engine Revving Too High
How a Lawn Mower Governor Works
Inside your lawn mower’s engine is a governor gear connected to the crankshaft. This governor gear spins a centrifugal flywheel which opens and closes in relation to the crankshaft. So as the engine runs at a higher RPM, the flywheel opens and engages the governor’s arm, then disengages the arm as the engine speed lowers. Look at the outside of your mower’s engine. You’ll see the governor arm connected to the governor link attached to the carburetor. This is where the governor controls the opening and closing of the throttle plate inside the carburetor as the load varies.
The last part of the governor system is the governor spring. The spring keeps tension on the governor so that it returns to the off position and opens the throttle plate. Without the correct tension, the throttle plate will not be adjusted correctly, and your engine will suffer one of the previously mentioned symptoms. So the whole governor system relies on the spring’s tension and adjustment.
Why a Lawn Mower Needs a Governor
If your lawn mower didn’t have a governor controlling the throttle plate inside the carburetor, then there would be no way to maintain a constant engine speed with varying loads. What does this mean? When you run your lawn mower over thick grass, your engine slows down since it has to work much harder. Without the governor, the engine would likely slow so much that it would stall. On the other hand, without any load, the engine would likely overspeed and run too fast without the governor. This leads to the engine running faster than it can handle, quickly resulting in a blown engine from overheating or failing engine components.
Symptoms of a Bad Governor Spring (A Closer Look)
Now let’s go over the different symptoms of a bad lawn mower governor spring and see how a faulty spring can affect your engine.
Problems Starting Your Lawn Mower
When your lawn mower engine is off, the governor system is disengaged. This means that the spring holds the governor system in the closed position, which, in turn, keeps the throttle plate fully open. The result is maximum airflow through the carburetor, which is necessary when starting your engine. However, if your governor’s spring is slack or missing, the governor will stay engaged. Depending on the throttle plate’s position, airflow into the carburetor could be reduced.
RPM Fluctuating and Surging Engine
If your governor spring is slack or missing, there’ll be nothing to control the throttle plate while your lawn mower engine is running. So, as you mow over varying grass thicknesses, you’ll hear your engine rev from high to low. This is a sign of a lawn mower engine surging and can occur not only when you are mowing but also when you simply engage the drive. This is because the power needed to drive your lawnmower’s wheels draws power from the engine.
Engine Bogging Down & Loss of Power
Most lawnmowers bog down when mowing thick or wet grass. This is pretty common. But having your mower bog down for no apparent reason is not something you should experience on a regular cut. Well, not if your governor is working correctly.
If the spring is slack or missing, it won’t apply the correct tension to the governor. When this happens, the governor won’t return, and the throttle plate will end up in the wrong position. So, the governor spring won’t open the throttle plate when the engine slows under load, and your lawn mower will bog down.
Engine Revving Too High
Sometimes, your governor’s spring gets too tight. This can happen when the spring is damaged, say from mowing under a hedge or incorrectly adjusting or installing the spring. Whatever the cause, the spring will hold the throttle plate fully open. As a result, your lawn mower engine will rev too high and overspeed while in use. Now, this is good when starting your mower but not while it’s running. So, you’ll definitely want to fix the spring ASAP.
What You Need to Replace a Small Engine Governor Spring(Tools & Parts)
When repairing your lawn mower’s governor spring, you’ll need to make sure you buy the correct spring. For example, a spring for a Briggs & Stratton engine isn’t the correct spring for a Honda engine, nor will it work on a Kohler engine. Here are a few examples of governor springs for different engines, which you will see look very different from one another.
Examples of Governor Springs
The only tool you should need to replace your governor spring is a pair of needle nose pliers. Sometimes getting the old spring off and the new spring on can be fiddly, so a pair of needle nose pliers over a pair of regular pliers comes in really handy. Alternatively, you could use a small spring puller tool specifically designed for installing springs without damaging them.
Example Tools
One thing to bear in mind is that engines have different designs. So, getting to the governor spring can differ from one lawn mower to the next. For example, lawn mowers such as Briggs & Stratton’s typically require removing the blower housing and gas tank to expose the governor spring location. So, you may need some other tools on hand just to get to the governor.
Example Additional Tools
How to Replace a Lawn Mower Governor Spring (The Steps)
Here are the steps to replace the governor spring on a Briggs & Stratton lawn mower. This lawn mower design requires a few additional steps since the spring is under the fuel tank. So, if your lawn mower is different, you can ignore these steps and tackle the governor spring itself.
Safety Steps
- Make sure that your lawn mower engine is cold.
- Disconnect the spark plug cable to prevent your engine from starting.
- Empty the gas tank or do this repair when the tank is empty.
Old Spring Removal Steps
- Release the start cord from the mower handlebars.
- Remove the blow housing (engine cover).
- Lift off the gas tank and set it to one side.
- Note the orientation of the governor spring
- Detach the old governor spring.
New Spring Installation Steps
- Position the new governor onto the lawn mower in the same orientation as the old spring.
- Attach the short end of the new spring to the mounting bracket.
- Attach the long end of the new spring to the governor lever.
- Install the gas tank.
- Replace the blower housing.
- Reattach the starter pull cord.
- Connect the spark plug.
- Fill the fuel tank.
Lawn Mowers With Governor Spring Adjustment
Depending on your lawn mower’s design, it may have some type of adjustment for the governor spring. Usually, it is a series of holes along the spring’s connection point. They allow you to either extend or tighten the spring. Normally, a new spring is connected to the first hole and then adjusted to the following holes as the spring stretches out. So, if you believe your governor spring has lost some tension, move the spring to one of the next holes. You’ll want to aim for the middle ground where the engine doesn’t over-speed or under-speed.
Other Potential Governor Spring Problems
The governor system is made up of various parts, and the spring is not always the cause of the problem. Any part of the governor system could be at fault. If you’ve checked your spring and it looks fine, here are other areas to inspect:
- Governor gears inside the engine
- Governor arm passing through the engine
- Governor link bar between the engine and the carburetor
- Governor link bar connection to the governor arm
- Governor link bar connection to the carburetor
Usually, the spring is the root cause since it’s the weakest part of the system and is known for stretching out. In my experience, it’s best to start by inspecting the spring and then work through the list of other potential governor issues.
