MTC Engine Performance & Tuning 2

Question 1

What does a high vacuum reading on a manifold vacuum gauge (18-22 in. Hg at idle) typically indicate?

Accepted Answer

Normal engine operation

Answer

A steady 18-22 in. Hg vacuum at idle indicates the engine is running normally with good ring seal and proper valve operation.

Question 2

When tuning a carbureted marine engine, which jet size change would richen the mixture at wide-open throttle?

Accepted Answer

Larger main jet

Answer

A larger main jet allows more fuel flow at WOT, enriching the air/fuel mixture for increased power or to address lean conditions.

Question 3

A marine engine exhibits detonation (knock) under load. Which of the following is the MOST likely cause?

Accepted Answer

Ignition timing too advanced

Answer

Over-advanced ignition timing causes the air/fuel mixture to ignite too early, leading to detonation under load.

Question 4

Which tool is used to measure crankshaft end play during engine assembly?

Accepted Answer

Dial indicator

Answer

A dial indicator measures crankshaft end play by measuring axial movement when force is applied to the crankshaft.

Question 5

On a four-stroke marine engine, what stroke follows the compression stroke?

Accepted Answer

Power stroke

Answer

After the compression stroke compresses the air/fuel mixture, the spark plug fires initiating the power (combustion) stroke.

(MTC) Marine Technician Certification Practice Test