EETC Carburetor Service and Repair 2

Question 1

What tool is required to adjust the mixture screw on many EPA-compliant carburetors equipped with limiter caps?

Accepted Answer

Splined or D-shaped limited adjustment tool

Answer

EPA-compliant carburetors use tamper-resistant limiter caps that require a special splined tool to restrict how far the mixture can be enriched.

Question 2

What symptom most clearly indicates the idle mixture screw is set too lean?

Accepted Answer

Engine runs rough and tends to stall at idle speed

Answer

A lean idle mixture provides insufficient fuel for stable combustion at low rpm, causing rough running or stalling.

Question 3

What is the correct initial starting position for a typical carburetor mixture screw before fine-tuning?

Accepted Answer

1 to 1.5 turns out from lightly seated

Answer

Starting at 1–1.5 turns out from lightly seated provides a safe baseline mixture that allows the engine to start for final adjustment.

Question 4

Which carburetor adjustment directly sets the engine idle speed?

Accepted Answer

Turning the throttle stop screw in or out

Answer

The throttle stop screw mechanically limits how far the throttle plate closes, setting the minimum airflow and engine idle speed.

Question 5

What is the correct method for verifying carburetor adjustment after making changes?

Accepted Answer

Test performance at idle, mid-range, and full throttle under actual load

Answer

Each throttle range uses a different carburetor circuit, so adjustment must be verified across all operating conditions to confirm proper tuning.

EETC - Equipment & Engine Training Council Practice Test