Carburettor fundamentals — control of mixture quantity and ratio in SI engines Evaluate the statement: “The function of a carburettor is to control the amount and ratio of the air–fuel mixture.”

Introduction / Context:
Before electronic fuel injection became universal, carburettors were the standard devices for metering fuel and mixing it with intake air in spark-ignition engines across operating conditions.

Given Data / Assumptions:

• Conventional float-type carburettor with jets, venturi, throttle plate, and enrichment circuits.
• Normal running modes: idle, part load, acceleration, power, and choke for cold start.

Concept / Approach:
The carburettor creates a pressure drop in the venturi as air flows. This draws fuel through calibrated jets. The throttle controls the total airflow (quantity), while jetting and auxiliary circuits influence the air–fuel ratio to meet engine demands.

Step-by-Step Solution:
Throttle opening sets airflow and therefore mixture quantity to the engine.Main, idle, and power jets plus air bleeds shape the mixture ratio across speeds and loads.Hence, the statement that a carburettor controls both amount and ratio of mixture is true.

Verification / Alternative check:
Tuning procedures adjust jet sizes and needle positions to correct mixture across the operating range, confirming control of ratio.

Why Other Options Are Wrong:

• False: contradicts the fundamental operation of carburettors.

Common Pitfalls:
Confusing throttle-only control (quantity) and forgetting that jets and circuits actively shape air–fuel ratio (quality).

Final Answer:
True