Seems that on my 26/27 engine, after start while adjusting the timing, I get to a point around the8:00 position on the quadrant and it smooths out. If I continue to advance the timeing, the idle speed picks up at around the 7:00 position, but I don't notice a smoother idle, just faster.
I presume when I take it out on the road, the settings will tweek a little. But, is one of the idle setting preferable to the other? The slower idle or the faster one?
I suggest the faster one. After all, when you drive off, the engine speed will rise, and you will not need LESS advance than at idle.
The correct timing is based on engine speed rather than car speed. That is if you rev up in low or Ruckstell, you can advance the spark farther, but when going slow, such as 22 mph in high the spark should be less advanced.
With that being said, the 8:00 position would be better for slower speeds such as 22-25 in high especially when pulling a hill, and the 7:00 position better for 35 or 40 mph.
The reason you notice the difference in engine speed change in "jumps" as the timing is advanced is when you run on magneto, the spark comes when the magnet passes the magneto coil. If you were running on battery, the spark would advance a little as the lever is advanced, but on magneto it depends on which coil the magnet is passing at that position of the timer.
Also, the engine will idle smoother on full retard on battery than on magneto. Usually you will need to advance from full retard about 4 notches for a smooth idle on magneto.
The idle is slower than you normally run the engine, so you can retard to about 9:00 position for smooth idle. And on top of all I have posted, is the initial setting of the timer and the amount of slack in the rod will affect those positions.