[san rensho]

So you are pushing the AFRs to lean? Lean produces more power, but you run the risk of burning up the motor. Although, 13 doesn't seem that radical. Isn't stochiometric around 14/1? If so, you are below that level.

When I used to race motorcycles, the 2 stroke guys with money had an interesting way of seeing how lean they could get. They would lean out the jets until the pistons siezed, then they would go one step rich, perfect! But expensive.

I'm assuming you are not running a closed loop fuel injection system, because the O2 sensors at the exhaust will send a signal to the DME to correct for the programmed AFR. No amount of tweaking the MAF will give you a different AFR in a closed loop system, just a CEL for an over/under limit of fuel trims., or am I missing something.