Too lean, Too rich, CCM, Best power, Best economy
August 3, 2024
Notes:
The carburettor measures the weight of air passing through the induction manifold and uses this measurement to regulate
the amount of fuel discharged into the air stream (according to a predetermined schedule).
What’s rich, lean and CCM?
Rich: 1:8
Chemically Correct fuel/air Mixture (CCM): 1:15
Lean: 1:20
In theory, the ‘correct’ quantity of fuel to mix with the air for complete burning, is one part of fuel to 15 parts of air, i.e., a fuel/air ratio of 0.067 (1:15).
How to achieve “best power” setting?
- slightly richer than CCM (because of complex chemical reactions associated with the predominance of
nitrogen in the air – beyond the scope of this book) - coincides with maximum cylinder head temperature (CHT)
- In practice, best power from 0.074 to 0.080 (1:13.5 to 1:12.5)
How to achieve “best economy” setting?
- achieved at fuel/air ratios at and just leaner than CCM
- also means “Minimum specific fuel consumption”
- In practice, best economy from 0.060 to 0.067 (1:16.5 to 1:15)
