Ohio Small Engine Mechanic Exam

Ohio Small Engine Mechanic Exam Practice Questions And Correct Answers (Verified Answers) Plus Rationales 2025|2026 Q&A | Instant Download Pdf

• What is the primary purpose of the carburetor in a small engine?

a) To cool the engine

b) To lubricate the crankshaft

c) To mix air and fuel in the correct ratio

d) To filter air entering the engine

Rationale: The carburetor’s job is to blend air and fuel properly

before combustion.

2. The air-fuel mixture is too rich when:

a) There is too much air

b) There is too much fuel

c) The spark plug is dry

d) The exhaust is clear 1 / 4

Rationale: A rich mixture has excess fuel, often causing black smoke

and fouled plugs.

• What type of engine is most commonly used in lawnmowers?

a) Two-stroke diesel

b) Four-stroke gasoline

c) Rotary engine

d) Electric hybrid

Rationale: Most lawnmowers use small four-stroke gasoline engines

due to efficiency and low emissions.

• What is the function of the governor in a small engine?

a) Starts the engine

b) Filters fuel

c) Regulates engine speed

d) Increases compression

Rationale: The governor controls throttle to maintain consistent

engine speed under varying loads.

• Which part ignites the air-fuel mixture in a small engine?

a) Carburetor

b) Valve

c) Spark plug

d) Piston

Rationale: The spark plug produces an electrical spark that ignites

the air-fuel mixture. 2 / 4

• What tool is used to check the spark plug gap?

a) Micrometer

b) Feeler gauge

c) Torque wrench

d) Vernier caliper

Rationale: A feeler gauge measures the small gap between spark

plug electrodes.

7. If an engine backfires through the carburetor, the most likely cause is:

a) Too much fuel

b) Weak spark

c) Incorrect valve timing

d) Dirty air filter

Rationale: Incorrect valve timing allows air-fuel to ignite while the

intake valve is open.

• What is the main cause of low compression in a small engine?

a) Dirty fuel

b) Worn piston rings

c) Cold temperature

d) Loose muffler

Rationale: Worn piston rings allow air-fuel leaks past the piston,

reducing compression.

9. When adjusting valves, the piston should be at:

a) Bottom dead center 3 / 4

b) Top dead center on compression stroke

c) Halfway down

d) Any position

Rationale: At TDC compression stroke, both valves are fully closed for

accurate adjustment.

• What is the most common cause of blue exhaust smoke?

a) Burning oil

b) Rich fuel mixture

c) Clogged air filter

d) Low compression

Rationale: Blue smoke indicates oil entering and burning in the

combustion chamber.

11. The flywheel key ensures:

a) Fuel mixture ratio

b) Correct ignition timing

c) Proper lubrication

d) Valve clearance

Rationale: The flywheel key aligns the flywheel and crankshaft for

correct spark timing.

12. A spark plug with black, sooty deposits indicates:

a) Rich air-fuel mixture

b) Lean air-fuel mixture

c) Proper combustion

• / 4