The soothing hum of a well-tuned lawn mower is a summertime soundtrack for many homeowners. But what happens when that peaceful hum turns into a frustrating, erratic revving that makes mowing more of a chore than a chore? A lawn mower that revs up and down can be a real headache, leaving you wondering what’s gone wrong and how to fix it. In this article, we’ll delve into the common culprits behind this frustrating issue, from fuel-related problems to engine malfunctions. We’ll also provide practical tips on how to troubleshoot and potentially fix the problem yourself.
Overview:
A lawn mower revving up and down, also known as “hunting,” can be caused by various factors. It often indicates a problem with the engine’s fuel delivery, air intake, or ignition system. Understanding these issues will help you diagnose and repair the problem, restoring your lawn mower to its smooth-running state.
Fuel System Troubles: The Root of the Problem
The fuel system is often the first place to look when a lawn mower starts revving erratically. A faulty fuel system can lead to inconsistent fuel delivery, resulting in the engine’s RPM fluctuating. Here’s a breakdown of common fuel-related issues:
1. Clogged Fuel Filter
The fuel filter prevents debris and sediment from reaching the engine, but it can also become clogged over time. A clogged fuel filter restricts fuel flow, causing the engine to starve for fuel, leading to erratic RPMs.
How to check:
- Locate the filter: The fuel filter is usually a small, cylindrical component near the fuel tank or fuel line.
- Inspect visually: Check for dirt, debris, or discoloration.
- Replace: If the filter is clogged or dirty, replace it with a new one.
2. Dirty Carburetor
The carburetor is responsible for mixing fuel and air before it enters the engine. Over time, dirt and debris can accumulate in the carburetor, hindering proper fuel and air mixture.
How to clean:
- Remove the carburetor: Carefully remove the carburetor from the engine.
- Disassemble: Take apart the carburetor and use a carburetor cleaning kit to thoroughly clean all parts.
- Reassemble: Put the carburetor back together, ensuring all parts are properly aligned.
- Replace gasket: Replace the gasket if it’s worn or damaged.
3. Fuel Line Problems
Cracked, damaged, or kinked fuel lines can restrict fuel flow to the carburetor, causing inconsistent fuel delivery and erratic engine speeds.
How to check:
- Visual inspection: Examine the fuel lines for cracks, leaks, or kinks.
- Replace: If any damage is found, replace the affected fuel line.
Air Intake Issues: A Breath of Fresh Air?
A lawn mower needs a steady flow of clean air to function correctly. Obstructed air intake can disrupt the fuel-air mixture and lead to erratic engine performance. Here’s what to look for:
1. Clogged Air Filter
The air filter protects the engine from dust and debris. A clogged air filter restricts airflow, causing the engine to run lean (with less fuel and more air), leading to engine instability.
How to clean:
- Remove and inspect: Remove the air filter and check its condition. If it’s dirty, remove the dirt with a brush or vacuum cleaner.
- Replace: If the air filter is damaged or beyond cleaning, replace it with a new one.
2. Leaky Air Intake
A leak in the air intake system can draw in unfiltered air, throwing off the fuel-air mixture and causing the engine to run poorly.
How to find leaks:
- Listen for hissing: Listen closely around the air intake and carburetor for hissing sounds that indicate a leak.
- Use carburetor cleaner: Spray carburetor cleaner around the air intake and carburetor while the engine is running. Look for changes in engine speed, which could indicate a leak.
- Inspect gaskets: Check the gaskets around the air filter, carburetor, and intake manifold for any damage or leaks.
Ignition System: Spark Plugs and Beyond
The ignition system is responsible for igniting the fuel-air mixture in the combustion chamber. A faulty ignition system can lead to misfires and inconsistent engine performance.
1. Worn or Fouled Spark Plug
The spark plug ignites the fuel-air mixture. A worn or fouled spark plug can lead to weak sparks, misfires, and erratic engine speeds.
How to check:
- Remove and inspect: Remove the spark plug and check for wear and tear. A worn-out spark plug will have a gap that’s too wide, or its electrodes may be damaged.
- Check the gap: Measure the spark plug gap using a spark plug gap gauge and adjust it according to the manufacturer’s specifications.
- Replace: If the spark plug is worn or fouled, replace it with a new one.
2. Ignition Coil Issues
The ignition coil delivers high voltage to the spark plugs. A faulty ignition coil can result in weak sparks, misfires, and erratic engine speeds.
How to check:
- Test with a multimeter: Use a multimeter to test the ignition coil for continuity and resistance.
- Visual inspection: Look for any signs of damage or corrosion on the ignition coil.
- Replace: If the ignition coil is faulty, replace it with a new one.
Other Potential Culprits
While fuel, air intake, and ignition system problems are the most common causes of erratic engine speeds, there are other factors that could be contributing to the problem:
- Governor Problems: The governor controls the engine’s speed. If the governor is faulty or misadjusted, it can lead to erratic RPMs.
- Engine Malfunctions: Severe engine problems, such as worn piston rings or a damaged valve, can also cause erratic engine speeds.
- Fuel Quality: Using low-quality fuel can lead to engine problems, including erratic RPMs.
- Air Temperature: Extreme temperatures can affect engine performance and lead to erratic RPMs.
Troubleshooting Tips
If your lawn mower is revving up and down, here are some troubleshooting tips:
- Start with the basics: Make sure the lawn mower has enough fuel, the spark plug is connected, and the air filter is clean.
- Check for leaks: Look for leaks in the fuel lines, air intake system, and exhaust manifold.
- Listen closely: Pay attention to any unusual sounds coming from the engine, such as hissing or knocking.
- Test the spark plug: Remove the spark plug and test it to ensure it’s firing properly.
- Check the carburetor: If the carburetor is dirty or gummed up, clean it thoroughly.
- Adjust the governor: If the governor is out of adjustment, try adjusting it according to the manufacturer’s specifications.
When to Seek Professional Help
If you’re unable to diagnose or fix the problem yourself, it’s best to take your lawn mower to a qualified mechanic. A mechanic can perform a comprehensive inspection and diagnose the issue more accurately. They can also repair or replace any faulty components.
Conclusion
A lawn mower that revs up and down can be a frustrating experience, but it’s not necessarily an insurmountable problem. By understanding the common causes and troubleshooting steps outlined in this article, you can often identify and resolve the issue yourself. If the problem persists or you lack the necessary experience, don’t hesitate to seek professional help. Remember, a well-maintained lawn mower will provide you with many years of reliable and smooth mowing.
Frequently Asked Questions
Why Is My Lawn Mower Revving Up and Down?
Here are 7 FAQs with answers for the article: Why Is My Lawn Mower Revving Up and Down?:
Q1: What causes a lawn mower to rev up and down?
A: A lawn mower revving up and down is often a symptom of an issue with the carburetor. This is the component responsible for mixing air and fuel, and if it’s not working correctly, it can cause the engine to fluctuate in speed. Other culprits can be clogged air filters, faulty spark plugs, or even a loose gas cap.
The engine may also be struggling to get enough fuel. Check the fuel lines and the fuel filter to ensure that they are not clogged. Finally, check the fuel tank to ensure it is full.
Q2: Is it safe to use a lawn mower that is revving up and down?
A: No, it’s not safe to use a lawn mower that’s revving up and down. This behavior could be a sign of a serious engine problem that could cause the mower to stall, backfire, or even catch fire. It’s best to stop using the mower immediately and try to diagnose the issue.
If the mower is still under warranty, it might be best to contact the manufacturer directly for assistance.
Q3: How do I fix a lawn mower that is revving up and down?
A: Fixing a lawn mower that’s revving up and down can be a bit tricky, and it may require some basic mechanical knowledge. You’ll need to start by diagnosing the problem, which can be done by checking the carburetor, air filter, spark plugs, and fuel lines.
Once you’ve identified the problem, you can try to fix it yourself or take the mower to a qualified mechanic. If the carburetor is the issue, you may need to clean it or replace it.
Q4: How do I clean the carburetor?
A: Cleaning the carburetor can be a messy job, but it’s often the first step in fixing a lawn mower that’s revving up and down. Start by disconnecting the fuel line and removing the carburetor from the engine.
Next, use a carburetor cleaner to spray out any dirt, debris, or gummed-up fuel. Let the carburetor dry completely before reassembling it and reconnecting the fuel line.
Q5: What should I do if my lawn mower is still revving up and down after cleaning the carburetor?
A: If cleaning the carburetor doesn’t solve the problem, there may be other issues with the engine. Consider replacing the spark plugs, air filter, or fuel lines. You may also want to check the fuel pump and fuel tank vent.
If you’ve tried all of these things and the lawn mower is still revving up and down, it’s best to take it to a qualified mechanic.
Q6: Can I use a lawn mower with a clogged air filter?
A: No, you should not use a lawn mower with a clogged air filter. The air filter prevents dirt and debris from entering the engine, and if it becomes clogged, the engine can’t get enough air to run properly.
This can lead to a variety of problems, including reduced engine power, increased fuel consumption, and even engine damage.
Q7: What are some preventative measures I can take to avoid a lawn mower revving up and down?
A: There are a few things you can do to help prevent your lawn mower from revving up and down. First, make sure to use high-quality fuel, and change the air filter regularly.
You should also check the spark plugs every season, and clean or replace them if needed. Finally, make sure to store your lawn mower properly during the off-season. This will help to prevent the carburetor from gumming up and the fuel lines from becoming clogged.