Erratic Timing

ScamperTom said
Yeah no kidding right about now I'm thinking it would be nice to have a computer handling this! I haven't messed with the spring perches yet; I want to be sure of what I have first.

OK I checked the timing curve again with a more reliable person watching the tach and I got the line in orange – much more reasonable. Some of the points could be off by a degree or so, but I'm confident I'm very close this time.
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I still can't get the idle to drop less than 100/150 rpm going into gear. And if I quickly jab the throttle, after revving up the engine drops another 100 rpm before returning to stable idle. If I brake when doing that it stalls the motor. It just lacks power at low idle. I've tried all kinds of timing: 8*-18* initial with and without vacuum advance, but it doesn't seem to help. I cracked the secondaries because the cam needed more air (not enough to get into the transfer slots); maybe this is causing a lean condition?

Its hard to be sure how accurate the tach and timing readings are. Plus/minus a degree is certainly to be expected.

Since this setup allows plenty of intial timing, use ported vac advance. Using manifold vac advance can be useful when its difficult to achieve enough initial mechanically and when small changes in vacuum caused by rpm or load change aren't going to effect the vacuum advance. I leave the vac supply hose plugged until the mechanical and initial are pretty well sorted out.

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. Its going to be iterative testing. 16 seems like the next step since you've tried it at 12 and 20 and you know 22 is too much and 8 is too little.

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. :)