Lawn Mower Troubleshooting Guide-Engine can be frustrating to attempt. It helps to have guide as to where to begin.

Lawn Mower Troubleshooting Guide-Engine can be frustrating to attempt. It helps to have guide as to where to begin when trying to diagnose any given problem. 

I have found this section of a much larger article covering many aspects of small engines to be very helpful. There is a lot of good Lawn Mower Troubleshooting Guide-Engine information here you may want to bookmark this page. 

Notes on the Troubleshooting and Repair of Small Gasoline Engines and Rotary Lawn Mowers 

Version 2.39 (28-Aug-07) Copyright © 1994-2007 Samuel M. Goldwasser 

--- All Rights Reserved ---

Instant troubleshooting chart - most common problems and possible causes


The following chart lists a variety of common problems and nearly all possible causes. Diagnostic procedures will then be needed to determine which actually apply. The 'possible causes' are listed in *approximate* order of likelihood. 

While this chart lists many problems, it is does not cover everything that can go wrong. However, it can be a starting point for guiding your thinking in the proper direction. 

(Portions of the following from: Chilten, Small Engine Repair 2-12 HP, (1).) 

Problem: Engine will not start or is hard to start. 
Possible causes:

1. Fuel tank is empty or shut off valve is closed, or fuel cap vent is plugged 2. There is water in the fuel. 3. Carburetor is over choked. 4. Carburetor is improperly adjusted or needs service. 5. Ignition system or its wiring is defective or ignition switch is off. 6. Dead man or other cutoff switch is open or defective. 7. Spark plug is fouled, improperly gapped, or damaged. 8. Engine compression is poor. 9.Operator needs to read user manual.

Problem: Engine starts easily but dies after a few seconds.

Possible causes:

1. Fuel tank is empty or shut off valve is closed, or fuel line or fuel cap vent is clogged 2. Carburetor is over choked. 3. Carburetor is improperly adjusted or needs service.

Problem: Engine idles roughly, unevenly, or surges.

Possible causes:

1. Carburetor is dirty. 2. Air leak in carburetor or intake manifold (e.g., bad O-ring, gasket, primer).3. Carburetor is improperly adjusted or needs service.

Problem: Engine misses under load.

Possible causes:

1. Spark plug is fouled, improperly gapped, or damaged. 2. Breaker points are pitted or improperly gapped, breaker arm is sluggish, or condenser is bad. 3. Carburetor needs adjustment or service. 4.Fuel line, fuel filter, or fuel tank cap vent is clogged, or fuel shut off valve partially closed. 5. Valves not adjusted properly or valve springs weak. 6. Exhaust ports blocked (2 stroke).

There are solutions here in the Lawn Mower Troubleshooting Guide-Engine

Problem: Engine knocks.

Possible causes:

1. Magneto is not timed properly. 2. Carburetor is set too lean. 3. Engine has overheated. 4. Carbon build up in combustion chamber. 5. Flywheel is loose. 6. Connecting rod is loose or worn. 7. Cylinder is excessively worn.

Problem: Engine vibrates excessively.

Possible causes:

1. Engine is not mounted securely. 2. Blade or other driven equipment is unbalanced. 3. Crankshaft is bent. 4. Counterbalance shaft is not timed correctly.

Problem: Engine lacks power (possibly after warm up)

Possible causes:

1. Old gas, bad spark plug, very thick/dirty oil. 2. Choke is partially closed. 3. Carburetor needs adjustment or service. 4. Ignition not timed correctly. 5. Air filter is clogged. 6. There is a lack of lubrication. 7. Valves are not sealing properly. 8. Piston rings are not sealing properly. 9. Head loose or head gasket blown or damaged. 10. Exhaust ports blocked (2 stroke).

Problem: Engine operates erratically, surges, and runs unevenly.

Possible causes:

1. Fuel line or fuel tank cap vent is clogged. 2. There is water in the fuel. 3. Fuel pump is defective. 4.Governor is not set properly, sticking, or binding. 5. Carburetor needs adjustment or service. 6. Loose carburetor/intake pipe resulting in vacuum leak.

Problem: Engine overheats.

Possible causes:

1. Magneto is not timed properly. 2. Carburetor set too lean. 3. Air intake or cooling fins are clogged.4. Shroud or blower housing missing. 5. Excessive load. 6. Insufficient or excessive oil. 7. Improper oil viscosity (4 stroke) or mixture (2 stroke) 8. Valve clearance is too small. 9. Excessive carbon build up in combustion chamber.

Problem: Crankcase breather passing oil.

Possible causes:

1. Too much oil in crankcase. 2. Engine speed is excessive. 3. Oil fill cap or gasket is damaged or missing. 4. Breather mechanism is dirty or defective. 5. Piston ring gaps are aligned. 6. Piston rings are worn.

Problem: Engine backfires.

Possible causes:

1. Carburetor set too lean. 2. Magneto is not timed correctly. 3. Valves are sticking.


If the previous information was of help to you and you would like to view the entire article please click here .

By having a basic guide when Lawn Mower Troubleshooting Guide-Engine you may save yourself many hours of anger and disappointment when you find out that it was something as simple as water in the gas that been preventing the mower from starting.

This information may also save you a lot of money by not having to take your mower right away to a small engine mechanic. Remember when ever you are working on your equipment think safety first.

I hope this helps with Lawn Mower Troubleshooting Guide-Engine.

“Keep It Simple to Succeed” lets get out there and make our lawns healthy and green!


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