in theory the leanes gasoline will burn is 18:1. the richest it will burn is 6:1
there are two different mixtures on either side of the centerline. The centerline is where there is exactly the ammount of fuel needed to completely burn with the ammount of fuel. The mixture is 15:1. It is refered to as the stoicheometric number. This is a mixture to be avoided since it is the mixture that produces the greatest ammount of heat. You can tell when at this mixture becasue the fire burns with a brilliant blue/white flame.
Now if you go leaner than stoicheometric you run into whats called best power lean which is around 16-16.5:1. But as we all know lean is bad becasue of its higher tendency to detonation.
If you go richer than stoicheometric you run into best power rich. This is about 11:1. This mixture yeilds more power than best power lean, and burns cooler, and is less likely to detonate, but under low throttle settings will cause carbon buildup inside the combustion chamber.
