Well done Don,
If my calculations are correct, that would be 9 Kg per 100 Km, or an gasoline replacement value of 6 Liters...
How much water did you use in your drip, compared with the charcoal used ?
What is your normal gasoline consumption when you drive ?
A steady RPM , with the minimum effort for the engine, will always give the lowest consumption, plus, of course, the weight been moved from one point to another.
One tip: i use iridium or platinium sparkplugs, they make a hell of a difference in low rpm torque