Question

Which among the following is provided in a vacuum advance type to keep the advance unit at zero if no vacuum is applied as during idling?

(a) Carburetor

(b) Diaphragm

(c) Centrifugal weights

(d) Return spring

I got this question in examination.

I'm obligated to ask this question of Ignition Advance topic in chapter Conventional Ignition System of Automotive Engine Design

Answer 1

Correct answer is (d) Return spring

The best explanation: A return spring on the vacuum side of the diaphragm keeps the advance unit at zero advance if no vacuum is applied as during idling. However, when the throttle is opened the vacuum is applied which moves the diaphragm against the return spring.