Erratic Timing

Mattax said
Since this setup allows plenty of intial timing, use ported vac advance.

Based on the rpm drop and the need to open the secondaries a crack, I think you should go for more initial timing than the 12*. 16*? and then retune the fuel mix.

That's what I'm thinking. Don't really need the extra timing and vacuum is all over the place at idle anyway. I'm gonna try bumping up the timing and closing the secondaries a little... Right now 16* and 18* idle well in park, but drop a lot in gear. In any case it's time to double check my T-ports.

Mattax said
Computer wouldn't be a lot of help. LOL. Vacuum or MAP is probably our best indicator of power and efficiency. Wideband O2 interpretations get fooled in situations like this, and they can't tell you what the power is. CO is more reliable indicator of fuel/air mixture at idle, but again doesn't tell us what the power is. We know from industry and military testing that idle AFR mixtures somewhere in the 13.5:1 range are the most efficient, but every engine is different and needs to be worked out emperically. Often more information is not all that helpful. If we turn a mixture screw 1/8 and observe the effect on the key objective, better vac or rpm in gear, what the WBO2 and CO meter indicates is not all the helpful. :)

TBH I wouldn't know how to work a diagnostics computer anyway. But you're totally right: I have to experiment on this engine, at the very least to figure out how engines respond in practice to changing parameters. Thanks again for the help! I think I'm getting there.