5 Things You Should Know in Small Engine Repair

small engine repair

We use small engines in several ways. Around the home, they can be found in lawn mowers, rototillers, trimmers, and edger that help keep our lawns looking good. They are also found in snowblowers, chainsaws, generators, and air compressors. 

When we feel like playing, they powerboat motors, snowmobiles, motorcycles, ATVs, and other outdoor toys. To keep them running smoothly, they require maintenance and repair just like large gas motors do. If you own any of these, you should know the basics about small engine repair.

To be successful when performing small engine repair, it helps to be familiar with the parts of the engine and what they do. There are many individual components to a small engine and all are crucial to the proper operation of the engine. 

Let's look at the small gas engine, part by part.

About Small Engines

Small engines, like their larger cousins, are made of individual systems that must work in unison to produce the power needed to run our tools and toys.

Each of these systems is made of smaller parts. Knowing what to look for, and which system the trouble is connected to, is crucial to performing small engine repair. All small gas engines have six systems: fuel, ignition, combustion, lubrication, exhaust, and cooling.

Fuel System

No small gas engine can run properly without a smoothly running fuel system. If there is a problem in the fuel system, you may not get the amount of gas required for combustion.

Without combustion, your small engine will not run. To perform small engine repair, you need to become familiar with the parts of the fuel system.

bike fuel tank small engine repair

Image via Pixabay

Fuel Line

Gasoline travels from the tank to the pump or the carburetor through the fuel line. On a pressurized system, the fuel line will most likely have a squeeze bulb which builds pressure to move the gas.


The carburetor has a small opening which can be plugged by dirt and sediment that may be in the gas. The filter removes these particles before the gas enters the carburetor.

Fuel Tank

The fuel tank is just what it sounds like, a storage component for the gasoline used by the engine. There are two major kinds of fuel tanks, air-pressurized and those with a fuel pump. Both deliver the gas to the carburetor.


Non-pressurized tanks have a fuel pump. The pump creates a vacuum which pulls the gas from the tank and sends it to the carburetor.


The carburetor mixes the gas with the proper amount of air for the engine to run smoothly. If there is too much gas, then the mixture is rich, while too little gas creates a lean mix.


The throttle controls how much of the air/gas mix enters the engine. This controls the speed that the engine is running at.


The primer shoots a small amount of gas directly into the carburetor throat to make the start-up mixture rich. This helps a cold engine to start easier.


A choke reduces the amount of air going into the mix. This also creates a rich mix to start the engine.


This small component automatically opens the throttle when more power is required by the engine. It then closes the throttle when less power is needed.

Ignition System

This is the main system in a small engine. There are three kinds of ignition systems: a magneto-powered ignition, a battery-powered ignition, and a mechanical-breaker ignition.

All kinds create the spark that ignites the fuel for combustion. If there is no spark, there is no combustion. You need to know which ignition system you have for successful small engine repair.

car start-button-ignition-system small engine repair

Image via Pixabay

Magneto-Powered Ignition

A magneto uses magnetism to create electricity when there is no battery. The magneto is turned by a crankshaft which rotates when the starter cord is pulled. Magneto systems can be one of three kinds: mechanical-breaker, capacitor-discharge, and transistor-controlled.

Battery-Powered Ignition

Small engines with batteries used for starting also have an ignition coil that uses power from the battery to give spark to the spark plugs. They use the same ignitions as the magneto-powered ignition system.

Mechanical-Breaker Ignition

This system uses contact points and a condenser to send electricity to the spark plug. When the crankshaft turns, a cam opens and closes on a set of points which operate like an on/off switch.

When they are closed, it is on and when they open it shuts off. The condenser stores electric voltage to reduce the amount of spark moving across the points.


An ignition coil is just two lengths of wire wrapped around an iron core. The coil takes low voltage electricity and converts it into the high voltage charge that the spark plug needs.

Spark Plugs

The spark plug is inserted into the top of the cylinder. Electricity travel from the magneto or the coil to the spark plug.


Distributors are found on small engines with a spark plug and more than one cylinder. It distributes the spark to the correct cylinder in a specific firing pattern.

Combustion System

The combustion system is where the majority of the engine's work occurs.

car cylinder block small engine repair

Image via Pixabay

Cylinder Block

The cylinder block is the largest part of the small engine. It is basically a block of metal where the cylinder hole is located.

Cylinder Head

The cylinder head is the top of the cylinder and is bolted to the cylinder block. Some cylinder heads contain valves, depending on the type of motor.


The piston is at the bottom of the combustion chamber. It moves upward to compress the fuel/air mix for combustion. It then moves down to rotate the crankshaft.


The crankshaft is a metal shaft which the connecting rod is attached to. When the crankshaft turns, the piston moves; this movement rotates the crankshaft.

Connecting Rod

The connecting rod is between the piston and crankshaft. It has a bearing on one end that allows it to turn around the crankshaft. The other end is attached to the piston.


Valves are used to open and close passages within the combustion chamber. They are operated by changes in air pressure.


This weighted wheel is at the end of the crankshaft and delivers the power created by the engine to operate the tool or equipment. It also keeps the crankshaft turning properly.

Lubrication System

Friction will damage the movable parts of the engine, so proper lubrication, obtained through oil and grease, is essential to keeping your small engine running. Friction is also reduced by the bearings inside the engine.

bearing steel small engine repair

Image via Pixabay


The bearing is the part that absorbs most of the friction. Friction bearings contain a lubricant to lessen friction and a nonfriction bearing uses steel rollers or balls to prevent excess wear on the engine parts.


Viscosity is the term used to rate an oil's resistance to flow. Thicker oils have a higher viscosity.


As parts wear down due to friction, small pieces of metal break free. This needs to be filtered out to maintain the lubrication quality of the oil.

Exhaust System

car exhaust system small engine repair

Image via Pixabay

Spark Arrestor

A spark arrestor on the exhaust opening keeps the spark from exiting through the exhaust and possibly starting a fire. These are important on small motors that may be operated near easily combustible materials such as chainsaws, motorcycles, and lawnmowers.


Small gas engines create a considerable amount of noise. The muffler contains baffles which reduce the noise level of the exhaust gases.

Cooling System

Air-Cooling Fins

Metal fins around the combustion chamber move the hot air out and away from the chamber to keep the moving parts from over-heating.

Troubleshooting Checklist

When you need to do small engine repair, there are a few things you should ask yourself to help figure out what is wrong. Some questions to ask include the following:

  • Is the gas fresh?
  • Did I change the oil?
  • Is the carburetor plugged?
  • Do I need a new spark plug?
  • Is there smoke coming from the exhaust?
  • Are the safety features disengaged?
  • Am I starting it correctly?

5 Things You Should Know in Small Engine Repair

car engine repair oil change

Image via​ Pixabay

Listed below are five of the most common problems you will encounter when doing small engine repair.

Bad Gas

Bad gas makes the engine hard to start or runs rough. Gas deteriorates quickly and you should not store an engine with gas in it for an extended time.

Dirty Air

A dirty air filter will cause the pistons to seize up.

Needs Tuning

If your engine is running rough and smoking, it is due for a tune-up. You should change the plug, the oil, the filters, and clean the carburetor.

Too Much Gas

If you think your engine might be flooded, remove the spark plug. If it's wet, it's flooded.

Faulty Spark Plug

Replace your spark plug at the beginning of each season of use.


Knowing how to perform your own small engine repair can save you hundreds in repair costs. When you repair a part, tune up that entire system to save you time in the future and keep your motor running.

Featured Image via Pixabay

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.