Small engines power a significant portion of our outdoor equipment. From lawnmowers to leaf blowers, chainsaws to generators, these hardworking machines make our lives easier. But what happens when they refuse to start? A non-starting small engine can be incredibly frustrating, especially when you need it most. This article will explore the common reasons why your small engine might be failing to ignite and provide detailed troubleshooting steps to get it running again.
Fuel System Problems: The Prime Suspect
One of the most frequent culprits behind a stubborn small engine is an issue within the fuel system. Fuel is, after all, the lifeblood of the engine, and any disruption to its flow can prevent ignition.
Old or Stale Fuel: A Common Culprit
Gasoline doesn’t last forever. Over time, it can degrade, especially when left sitting in a fuel tank for extended periods. This is because gasoline contains volatile components that evaporate, and it can also absorb moisture from the air. This degradation results in a “stale” fuel that doesn’t ignite easily.
Always use fresh fuel. As a general rule, gasoline stored for more than 30 days can start to deteriorate. If your equipment has been sitting unused for a few months, it’s highly recommended to drain the old fuel and replace it with fresh gasoline. Adding a fuel stabilizer to fresh fuel can extend its lifespan, particularly during off-seasons.
Clogged Fuel Filter: Restricting the Flow
The fuel filter’s job is to prevent dirt, debris, and other contaminants from entering the carburetor and other sensitive parts of the fuel system. Over time, the filter can become clogged, restricting the flow of fuel to the engine.
Locate the fuel filter. It’s usually situated in the fuel line between the fuel tank and the carburetor. Inspect the filter for any visible signs of blockage. If it appears dirty or clogged, replace it with a new one. They are relatively inexpensive and easy to replace.
Blocked Fuel Lines: A Highway Interrupted
Fuel lines carry fuel from the tank to the carburetor. Like the fuel filter, they can become blocked with debris, or even collapse internally over time, restricting fuel flow.
Carefully inspect the fuel lines for any cracks, kinks, or blockages. You can try disconnecting the fuel line at both ends and blowing compressed air through it to dislodge any debris. If the line is cracked or damaged, replace it.
Carburetor Issues: The Fuel-Air Mixer
The carburetor is responsible for mixing fuel and air in the correct proportions for combustion. A dirty or clogged carburetor is a very common cause of starting problems. Small orifices and jets within the carburetor can easily become blocked with varnish from old fuel, preventing the engine from receiving the necessary fuel mixture.
Carburetors can be cleaned or rebuilt. Carburetor cleaner sprays are available to help dissolve deposits. In some cases, a complete carburetor rebuild may be necessary, involving disassembling the carburetor, cleaning all the parts thoroughly, and replacing any worn or damaged components. If you’re not comfortable working on carburetors, it’s best to take the equipment to a qualified service technician.
Fuel Tank Vent: Ensuring Proper Pressure
The fuel tank vent allows air to enter the tank as fuel is used, preventing a vacuum from forming. If the vent is blocked, it can create a vacuum that prevents fuel from flowing properly.
Check the fuel tank vent. It’s usually a small hole in the fuel cap. Ensure it’s clear of any obstructions. Sometimes, simply loosening the fuel cap can relieve the vacuum and allow the engine to start.
Ignition System Problems: Sparking the Flame
The ignition system is responsible for creating the spark that ignites the fuel-air mixture in the cylinder. If there’s no spark, the engine won’t start.
Spark Plug Issues: The Spark’s Source
The spark plug is a crucial component of the ignition system. It delivers the electrical spark that ignites the air-fuel mixture. A fouled, cracked, or improperly gapped spark plug can prevent the engine from starting.
Remove the spark plug. Inspect it for signs of fouling (carbon buildup), cracking, or damage. Clean the spark plug with a wire brush or spark plug cleaner if it’s fouled. Check the spark plug gap using a feeler gauge and adjust it to the manufacturer’s specifications. If the spark plug is cracked or damaged, replace it with a new one of the correct type.
Ignition Coil: Generating the Spark
The ignition coil is responsible for generating the high-voltage electricity needed to create the spark at the spark plug. If the ignition coil is faulty, it may not produce enough voltage to create a spark.
Test the ignition coil. This usually requires a multimeter to check its resistance. Consult your engine’s service manual for the proper testing procedure and resistance specifications. If the ignition coil is not within specifications, it should be replaced.
Kill Switch Problems: An Unintentional Shutoff
Most small engines have a kill switch that grounds the ignition system, preventing the engine from starting. A faulty kill switch or wiring can sometimes cause the engine to act as if it’s being turned off even when the switch is in the “on” position.
Check the kill switch and its wiring. Ensure that the switch is in the “on” position and that the wiring is not damaged or disconnected. You can try disconnecting the kill switch wiring to see if that allows the engine to start. If it does, the kill switch is likely faulty and needs to be replaced.
Compression Issues: Sealing the Deal
Compression is essential for proper combustion. The engine needs to compress the air-fuel mixture to a certain pressure to create the heat needed for ignition. If compression is too low, the engine won’t start.
Worn Piston Rings: Losing the Seal
Piston rings seal the space between the piston and the cylinder wall. Over time, these rings can wear down, reducing the engine’s compression.
Checking compression requires a compression tester. This tool is screwed into the spark plug hole, and the engine is cranked over to measure the pressure in the cylinder. Consult your engine’s service manual for the proper compression specifications. Low compression indicates worn piston rings or other internal engine damage.
Valve Problems: Controlling the Flow
The intake and exhaust valves control the flow of air and exhaust gases into and out of the cylinder. If the valves are not sealing properly, it can lead to low compression.
Valve problems can be diagnosed with a leak-down tester. This tool pressurizes the cylinder with air and allows you to listen for leaks coming from the carburetor (intake valve), the exhaust pipe (exhaust valve), or the crankcase (piston rings). Valve repairs are typically best left to experienced technicians.
Blown Head Gasket: A Major Leak
The head gasket seals the cylinder head to the engine block. If the head gasket is blown, it can create a leak that reduces compression.
Look for signs of a blown head gasket, such as oil leaks around the cylinder head or bubbles in the coolant (if the engine is liquid-cooled). A blown head gasket requires removing the cylinder head and replacing the gasket.
Other Potential Problems: The Unexpected
While fuel, ignition, and compression issues are the most common culprits, other factors can also prevent a small engine from starting.
Low Oil Level: Protecting the Engine
Many small engines have a low-oil sensor that prevents the engine from starting if the oil level is too low. This is a safety feature to protect the engine from damage.
Check the oil level and add oil if needed. Ensure that you’re using the correct type of oil for your engine.
Sheared Flywheel Key: Timing Trouble
The flywheel key is a small key that connects the flywheel to the crankshaft. If the flywheel key shears, it can throw off the engine’s timing, preventing it from starting.
Inspecting the flywheel key requires removing the flywheel. Look for signs of damage to the key. If it’s sheared, it needs to be replaced.
Choke Problems: Starting Cold
The choke restricts airflow to enrich the fuel mixture for cold starting. If the choke is not working properly, it can prevent the engine from starting, especially in cold weather.
Ensure that the choke is functioning correctly. When the engine is cold, the choke should be closed or partially closed. As the engine warms up, the choke should gradually open.
Flooded Engine: Too Much Fuel
If you’ve been cranking the engine repeatedly without success, you may have flooded it with too much fuel.
Try these steps to start a flooded engine. Turn off the choke. Set the throttle to the wide-open position. Crank the engine for several seconds to clear out the excess fuel. Then, try starting the engine again with the choke in the correct position.
Final Thoughts: Persistence Pays Off
Troubleshooting a non-starting small engine can be challenging, but by systematically checking each potential problem area, you can often diagnose and fix the issue yourself. Remember to always consult your engine’s service manual for specific instructions and specifications. If you’re not comfortable performing any of these repairs, it’s best to take the equipment to a qualified service technician. With a little patience and perseverance, you can get your small engine running smoothly again and get back to tackling your outdoor tasks.
Why is my small engine cranking but not starting?
Your small engine cranking but failing to start often points to a fuel or spark issue. Begin by checking if there’s fuel in the tank and that it’s reaching the carburetor. A clogged fuel line, a dirty fuel filter, or a malfunctioning fuel pump can prevent fuel from reaching the engine. Also, verify that the spark plug is clean, properly gapped, and producing a strong spark.
If fuel delivery seems fine, focus on the ignition system. A faulty ignition coil, a damaged spark plug wire, or a malfunctioning kill switch could be preventing the spark necessary for combustion. Use a spark tester to confirm the spark plug is firing correctly. If the spark is weak or absent, replace the spark plug and test the coil’s output.
How do I check the spark on my small engine?
The easiest way to check the spark on your small engine is by using a spark plug tester. Connect the tester to the spark plug wire and ground it against the engine block. Then, pull the starter rope or turn the key (depending on your engine type). Observe the tester; a bright, consistent spark indicates a healthy ignition system.
Alternatively, you can carefully remove the spark plug, reattach it to the spark plug wire, and hold the metal base of the plug against a clean, unpainted metal surface on the engine block. While holding it securely, pull the starter rope. A visible blueish-white spark jumping across the spark plug gap indicates proper spark. If you don’t see a spark or it is weak and orange, the spark plug or ignition system may be faulty. Use extreme caution when performing this test to avoid electrical shock.
What if my small engine has been sitting unused for a long time?
When a small engine sits idle for an extended period, fuel can degrade and gum up the carburetor. Old fuel can leave behind varnish and deposits that clog jets and passages, preventing the engine from starting. The stale fuel can also absorb moisture which causes rust and corrosion.
The best approach is to drain the old fuel completely from the fuel tank and carburetor bowl. Clean the carburetor thoroughly, paying special attention to the jets. Consider using a carburetor cleaner or rebuild kit. After cleaning or rebuilding, refill the tank with fresh fuel and try starting the engine. Use a fuel stabilizer in your fuel for future storage.
Why is my small engine hard to start when it’s cold?
Cold weather makes it harder for fuel to vaporize, which is necessary for combustion. This can be compounded by a weak battery (in engines with electric start), or thick oil that makes the engine harder to turn over. Small engines often require more priming or choking in cold conditions to enrich the fuel mixture.
Try priming the engine several times before attempting to start it. Ensure the choke is fully engaged. For electric start engines, make sure the battery is fully charged and capable of providing sufficient cranking power. If these methods don’t work, consider using a small engine starting fluid sparingly, following the instructions on the product label.
What does it mean when my carburetor is flooded?
A flooded carburetor means there is too much fuel in the combustion chamber, preventing the engine from firing properly. This is often caused by excessive priming, a stuck float valve in the carburetor, or a leaking needle valve. The excessive fuel displaces the air required for combustion.
To address a flooded engine, first, turn off the fuel supply. Then, remove the spark plug and pull the starter rope several times to clear excess fuel from the cylinder. Allow the cylinder to air out for a few minutes. Reinstall the spark plug, and try starting the engine without using the choke or primer. If the engine starts, gradually open the choke as it warms up.
My small engine starts but dies immediately. What could be wrong?
If your small engine starts briefly and then dies, it’s often a sign of a fuel delivery problem. The engine might be running on the fuel initially drawn into the cylinder during priming, but then starves for fuel once that initial supply is exhausted. A partially clogged fuel filter, a blocked fuel line, or a malfunctioning fuel pump can cause this issue.
Another possibility is a problem with the carburetor itself. A dirty or partially blocked jet might be restricting fuel flow. Check the vent in the fuel tank cap to ensure it’s not blocked, as this can create a vacuum that prevents fuel from flowing. Also, look for any air leaks in the intake manifold, which can lean out the fuel mixture and cause the engine to stall.
How do I prevent starting problems with my small engine?
The best way to prevent starting problems is through regular maintenance and proper storage practices. Always use fresh fuel and add a fuel stabilizer, especially when storing the engine for extended periods. Regularly inspect and clean or replace the air filter, spark plug, and fuel filter.
Properly winterize your engine before storing it for the off-season. This includes draining the fuel tank and carburetor bowl, changing the oil, and lubricating moving parts. Following these preventive measures will significantly reduce the likelihood of starting problems when you next need to use your small engine.