Troubleshooting a Lawnmower That Won't Start: Common Issues and Solutions
There are numerous reasons why your lawn mower might refuse to start. For many, it often comes down to a lack of regular maintenance, a common issue known as benign neglect, which can lead to the demise of many mechanical devices. If you are unable to diagnose the problem yourself, it's crucial to seek professional help to fix the mower, unless you have the necessary skills to repair it yourself. This guide delves into the three key elements required for any internal combustion engine to run: air, fuel, and spark. Additionally, we will address modern safety features and provide detailed checks for each of these elements.
Understanding the Basics
The air, fuel, and spark are the three essential ingredients needed for a lawn mower to start. If any one of these is missing or malfunctioning, the mower will not start. Here’s a breakdown of each:
Air
Make sure the air filter is in good condition. A dirty air filter can restrict airflow to the engine, preventing it from starting. To check the air filter, simply remove it and inspect it for dirt or debris. If it's dirty, clean it according to the manufacturer's instructions or replace it with a new one.
Fuel
Check for any fuel issues. Remove the air filter and look inside the throat of the carburetor for any fuel or a squirt of accelerant like starting fluid (WD-40). If the engine fires, it suggests the carburetor might be dirty or plugged up from old fuel. Clean the carburetor thoroughly, or if it's too severely gummed up, replace it.
Check the fuel tank for any contamination or dirt. Ensure there is enough fuel and that it hasn't gone bad. If you have left fuel in the mower over the off-season, it's essential to address any water contamination or other impurities that could impair starting.
Spark
Verify the spark by removing and grounding the spark plug. If it doesn't spark, check for a short circuit. Disconnect the kill switch wire from the engine and check if it sparks. If there is no spark, test the spark plug with a known good one. If the spark plug is faulty or the ignition coil is bad, replace it as needed.
Safety and Ignition Issues
Modern lawn mowers are equipped with various safety features, such as blade interlocks, which can prevent the mower from starting if certain actions are not met. These safety devices are designed to enhance user safety but can also create starting issues. Make sure to test the mower for any interlocks or safety mechanisms that need to be activated for the mower to start.
Physical and Mechanical Issues
If everything checks out with air, fuel, and spark, move on to check for physical and mechanical issues:
Flywheel Key
Inspect the flywheel key. If it is sheared, replace it as it can affect the ignition timing. Check the key before further troubleshooting to avoid skipping crucial steps.
Compression Tests
Test the engine's compression using a test gauge. If the compression is low, it might be due to worn piston rings. Consider adding a squirt of oil through the spark plug hole. If this improves the compression, the rings are likely worn. If not, check for issues like a blown cylinder head gasket or holding open valves.
For L-headed engines (e.g., Briggs and Stratton or Tecumseh), remove the cylinder head, muffler, and PCV valve to adjust the valve clearance. Grind down the valve stem slightly to obtain the required clearance. Once the valves are adjusted, lap the valves to ensure optimal performance.
Check the valve timing marks and align them correctly. If the engine still fails to start, it might indicate a bad camshaft. In severe cases, the piston may need to be removed and either the rings replaced or the camshaft reset or replaced.
Conclusion
With these detailed steps, you should be able to identify and resolve most common issues that prevent your lawnmower from starting. Remember, regular maintenance is key to keeping your mower in top condition. If you're unsure, don’t hesitate to bring it to a professional for troubleshooting and repair.