Common terms for small engines

A

Air Filter
A replaceable filter that prevents dirt and debris from entering the engine.

Air-Fuel Mixture
The combination of gasoline and air is required for combustion.

Alternator
A component that generates electricity while the engine is running.

Anti-Backlash Pawl
A safety device in chainsaws that stops chain rotation if kickback occurs.Anti-Vibration Mounts
Rubber mounts that reduce engine vibration on chainsaws, trimmers, and mowers, making operation smoother and safer.

B

Backfire
A loud popping sound caused by unburned fuel igniting in the muffler. Backfiring in a lawn mower or small engine is often caused by carburetor issues, incorrect timing, or stale fuel.

Blade Adapter
The metal part that connects the mower blade to the crankshaft. A damaged blade adapter can cause vibration or uneven cutting.

Blower Housing
The outer engine cover that directs cooling air around the cylinder. If blocked, your engine can overheat.

Bore
The diameter of the cylinder inside the engine. Bore size affects engine displacement and power output.

C

Camshaft
Controls the opening and closing of engine valves. If a camshaft is worn or damaged, your small engine may lose power or compression.

Carburetor
A carburetor mixes fuel and air before it enters the engine. A dirty carburetor is one of the most common causes of a lawn mower that won’t start.

Carburetor Jet
A tiny opening inside the carburetor that controls fuel flow. Clogged jets often cause engine surging or stalling.

Choke
Restricts airflow to create a richer fuel mixture when starting a cold engine. If the choke stays on too long, the engine may flood.

Compression
The pressure inside the engine cylinder. Low compression can cause hard starting, loss of power, or an engine that won’t start at all.

Crankshaft
Converts the up-and-down movement of the piston into a spinning motion that powers your mower blade or chainsaw chain.

Cutting Deck
The housing around a lawn mower blade.

D

Decompression Valve
A feature found on some chainsaws and larger small engines that makes pull-starting easier by temporarily lowering compression.

Dipstick
Used to check engine oil level. Running a small engine with low oil can cause severe engine damage.

Displacement (CCs)
Measured in cubic centimeters (CC), displacement tells you the size of the engine. Higher CC engines typically produce more power.

Drive Belt
Transfers engine power to mower wheels or blades. A worn belt may cause slipping or loss of movement.

E

Electric Start
A system that uses a battery and starter motor to start the engine instead of a pull cord.

Engine Flooding
Occurs when too much fuel enters the combustion chamber, often from excessive choking. A flooded lawn mower may smell strongly of gasoline and refuse to start.

Engine Surging
When the engine repeatedly speeds up and slows down while running. This is commonly caused by carburetor problems or fuel flow restrictions.

Exhaust Port
The opening where burned gases exit the engine. Carbon buildup can restrict airflow and reduce power.

F

Flywheel
A heavy rotating wheel that keeps the engine running smoothly. It also helps generate a spark in magneto ignition systems.

Fuel Filter
Prevents dirt and debris from entering the carburetor. A clogged fuel filter can cause stalling or hard starting.

Fuel Line
The hose that carries gasoline from the tank to the carburetor. Cracked or leaking fuel lines can cause starting issues.

Fuel Stabilizer
An additive that prevents gasoline from breaking down during storage. Using fuel stabilizer helps prevent carburetor problems after winter storage.

Four-Stroke Engine
A type of small engine that completes combustion in four steps: intake, compression, power, and exhaust. Most lawn mowers use four-stroke engines.

G

Gas Cap Vent
Allows air into the fuel tank as gasoline is used. A blocked vent can cause the engine to stall after running briefly.

Gasket
A seal placed between engine parts to prevent air, oil, or fuel leaks.

Governor
Automatically controls engine speed under load. If the governor fails, your mower may run too fast or too slow.

H

Head Gasket
Seals the cylinder head to maintain compression. A blown head gasket may cause white smoke or oil leaks.

Horsepower (HP)
A measurement of engine power. Higher horsepower means more cutting or pulling capability.

Hydrostatic Transmission
A smooth, gearless drive system found on many riding mowers that allows variable speed control.

I

Idle
The engine speed when running without cutting grass or under load. A rough or uneven idle is often caused by carburetor issues.

Idle Screw
An adjustment screw on the carburetor that controls idle speed. Improper adjustment can cause stalling.

Ignition Coil
Creates the high voltage needed for the spark plug to ignite fuel. A bad ignition coil can cause no spark and a mower that won’t start.

Impeller
A rotating component in snow blowers and pressure washers that moves air or water.

Intake Valve
Allows the air-fuel mixture to enter the combustion chamber.

J

Jet (Carburetor Jet)
A small passage inside the carburetor that controls fuel flow. Clogged jets are a common cause of engine surging.

Jump Start (Small Engine)
Using an external battery to start riding mowers or generators with an electric start.

K

Kickback
A sudden upward motion of a chainsaw caused by chain contact with a hard object. Proper chain tension and technique reduce risk.

Kill Switch
A safety switch that stops the engine by grounding the ignition system.

L

Lean Mixture
An air-fuel mixture with too much air and not enough fuel. A lean condition can cause overheating or engine damage.

Lubrication
The process of reducing friction using engine oil. Proper lubrication prevents premature engine wear.

Low-Oil Shutdown
A safety feature that automatically stops the engine when oil levels drop too low.

Lawn Mower Deck
The housing that surrounds the mower blade and directs grass flow.

M

Magneto
A self-contained ignition system that generates a spark without a battery.

Main Jet
The primary carburetor jet controls fuel flow at higher engine speeds.

Muffler
Reduces engine noise and directs exhaust gases away from the operator.

Mulching Blade
A specially shaped mower blade that chops grass into fine clippings.

N

No-Start Condition
When a small engine will not start. Common causes include bad fuel, a clogged carburetor, a faulty spark plug, or low compression.

Needle Valve
A carburetor component that controls fuel flow into the float bowl.

O

Oil Capacity
The amount of oil required for proper lubrication. Always check your owner’s manual for correct oil levels.

Oil Viscosity
The thickness of engine oil. Using the correct viscosity helps prevent engine wear.

Overhead Valve (OHV)
An engine design that improves efficiency and power output.

Overheating
Occurs when airflow is restricted or oil levels are low. Overheating can permanently damage a small engine.

P

Piston
Moves up and down inside the cylinder to create engine power.

Piston Rings
Seal the piston against the cylinder wall to maintain compression.

Pull Cord
The rope used to manually start a small engine.

Power Take-Off (PTO)
Transfers engine power to blades or attachments.

Primer Bulb
A small rubber bulb that pushes fuel into the carburetor to assist starting.

Q

Quick-Release Blade
A blade system designed for easier blade removal and maintenance.

R

Recoil Starter
A spring-loaded pull-start mechanism is used to start most small engines.

Rich Mixture
An air-fuel mixture containing too much fuel. Can cause black smoke and poor performance.

RPM (Revolutions Per Minute)
Measures engine speed. Most lawn mowers operate around 3,000–3,600 RPM.

Rocker Arm
Transfers camshaft motion to open and close valves.

S

Spark Plug
Creates the spark that ignites the air-fuel mixture. A dirty spark plug is a common reason a lawn mower won’t start.

Spark Plug Gap
The distance between spark plug electrodes. An incorrect gap can cause misfires.

Starter Solenoid
An electrical switch that activates the starter motor.

Stroke
The movement of the piston from top to bottom inside the cylinder.

T

Throttle
Controls engine speed by adjusting airflow and fuel intake.

Timing
The precise coordination of spark and valve operation. Incorrect timing can cause backfiring.

Two-Stroke Engine
An engine that completes combustion in two piston movements. Common in chainsaws and trimmers.

Tensioner
Maintains proper belt or chain tension.

U

Unleaded Gasoline
The standard fuel used in most small engines.

Upper Cylinder Lubricant
An additive that helps reduce wear in two-stroke engines.

V

Valve Clearance
The small gap between valve components allows proper operation.

Valve Lash
Another term for valve clearance. Incorrect lash can cause hard starting or power loss.

Volute
The curved housing in blowers directs airflow.

W

Walk-Behind Mower
A push mower powered by a small gasoline engine.

Winterization
Preparing a small engine for storage by stabilizing fuel and changing oil.

X

X-Torque (Chainsaw Technology)
A fuel-efficient two-stroke engine design used in some modern chainsaws.

Y

Yard Equipment
Outdoor tools powered by small engines, such as mowers, trimmers, and blowers.

Z

Zero-Turn Mower
A riding mower that can turn in place using independent wheel motors for tight maneuverability.