Question

If the engine is operating with richer mixtures the optimum spark timing must be _____________

(a) constant

(b) increased

(c) retarded

(d) none of the mentioned

I had been asked this question in class test.

My question is based upon Ignition Timing and Engine Parameters in portion Ignition of IC Engine

Answer 1

Correct option is (c) retarded

To explain: If the engine is operating with richer mixtures the optimum spark timing must be retarded as if the mixture is rich it has its low self ignition temperature.