Erratic Timing

Mattax said

That does suggest its not too radical. It still might like a curve with a little more advance in the begining. Funny thing is that electronic ignition distributor's curve may already do that for you!

Sketched the '72 maximum timing onto the '68, and also marked your 1* at 1100 rpm.
Based on what you've posted, if you can get 5* at 800, that would be pretty good. Then see how it drives.
View attachment 1715307121

If it has some cam in it, it may not like 0* or even 5* at 600 rpm.
If it is some cam, probably will like an initial more like a pre-smog 273 4bbl (or maybe a police pursuit 318 4bbl using a 340ish cam, I've not seen those timing curves)

Click to expand...

I've been looking at the figures I wrote down, and realized that I can't remember if I set the initial timing at 10* or 0* to record them... so they're pretty much useless. Either way they seem fairly close to the stock 318 specs you posted. Quick short advance at first then a long slow curve.

I worked on the idle tuning a bit this afternoon and was pretty successful I think. I realized I had previously cracked the secondaries open too far, so I closed them and was able to drop the idle down to 600 in gear, 750 in park with 10* of initial timing. Any more and it would kick back on the starter (is that technically detonation?) That should allow me to approximate the 273 curve you posted. If I aim for 32* total (how close should I really push it for a mild engine?) then my vacuum can should come in just about perfect, theoretically.