timing vs lean-rich condition

[cole18cars]

Hello, I'm wondering what effect timing has on a lean or rich condition? Thanks

[martybose]

As an oversimplification, advancing timing will be like leaning it out, while retarding ignition timing will be like fattening it up.

Marty

[greg g]

I would think it makes no difference. The fuel to air mix is what it is as determined by the circuits, and jets in the carb and the amount of air being sucked through the carb.

Timing only effects when the mix is fired off in relation to the stroke of the piston within the cylinder. At idle at tdc, the spark is delivered when the Fuel air mix is at is mosed compressed. Retarding the timing would fire it off after the piston has started it travel down the cylinder. this would lessen the push on the piston both through distance travelled and the fact that compression is past its peak. the reason the distributor advances timing as rpms increase it to time try to match the firing of the fuel as the piston reaches tdc. so that the biggest push occurs over the greatest distance. Remember there is a thing called flame front, the whole mixture just doesn't burst immediatly into flame the flame travels from the point of ignition to fill the cylinder on top of the piston then as it expands it pushes down on the piston.

A retarded spark will give a less effecient burn leaving more unburned fuel giving the impression (smell, black smoke) of a rich mix. But so will a timing setting that fires off to early before the mix is properly compressed.

There are two way you can effect the fuel air mix, restrict the air flow, or enlarge the jets. Other wise you got what your carb gives you.