[Halon]

On the Link forums, one of the guys mentioned that he aims for 12.0:1. He says he doesn't see much gains going any leaner then 12.5:1, so he stops at around 12.0 and then just starts adding timing instead of going leaner as he sees better results by adding timing at that point rather then leaning it more. He just adds timing until he starts seeing knock.

As far as Lambda, I believe you are just aiming for 1 no matter what your fuel.