How does engine timing effect emissions?

[243]

I need to reset the timing if neccessary for the upcoming smog test.

Within reason, what has the best effect on emissions, advanced or retarded?

That is, if 8deg BTDC is "by the book", will 6deg BTCD or 10deg BTDC be best?

Thanks,

[Brown Bear]

Advancing the timing will create more vacuume pressure. I believe this will lean out the mixture.

[Sgt. Dave]

243, go for the "book" setting, or no more than 2 more degrees advance. What are you trying to achieve? Emissions check at idle or a part throttle test? I don't know what they check where you are, or how they do it. Is it a visual inspection, or a sniffer test? You might also reset the idle mixture to a 50 rpm lean of best idle setting.