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Lean burn refers to the burning of fuel with an excess of air in an internal combustion engine. In lean burn engines the air:fuel ratio may be as lean as 65:1 (by mass). The air:fuel ratio needed to stoichiometrically combust petrol, by contrast, is 14.64:1. The excess of air in a lean burn engine combusts more of the fuel and emits fewer hydrocarbons. High air–fuel ratios can also be used to reduce losses caused by other engine power management systems such as throttling losses.
Engines run rich idling. Mix is leaner as throttled, until torque is needed, and a richer mix is needed. A med load needs a lean mix.
Not all engines have perfectly equal air distribution to the chambers, without sensors in each individual piston cyclinder, not all will be exactly running equally since the exhuast is measured from all cyclinders.
With a vapor, any engine would receive the same air fuel mixture regardless of imperfections in fluid flow and turbulence in the intake manifold. Results would be a better balanced engine, which is inherently more efficient.
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