<VV> What's the relation between ignition timing and running rich or lean?

[Guus de Haan]

Saturday I changed the jet on the Carter YH to a bigger size. I want  
the car to run a but more rich. Took it for a fast (70-80 mph) drive  
on the highway and temperature and A/F ratio looked good.

Then I changed the temporarily installed points plate back to the  
Ignitor (series I) that was in before. This required adjusting the  
timing a bit and I thought the A/F on the SafeGuard showed the car to  
run a bit more lean again.

Is there someone who can explain to me what's the influence of  
ignition timing on the engine running rich or lean? I like to  
experiment but also would like to know the why of things.

Thanks,

Guus de Haan
The Netherlands
'65 Corsa Turbo-Charged Cvt