Have an 81 sc,
I'm starting to believe that though the distributor moves freely, the notch in the timing curve down low where advance meets delay makes rpm at 950rpm sort of jog around when the oil is warm, usually just above the trombone opening.
Maybe 800 to 850rpm set warm it will never move once warm, bug will be lower during warmup. When set to 900 rpm warm, lights on, clutch out, either or both will stablilize the rpm at 850/900, otherwise it might start bouncing off of 1050 rpm or so over a decently warm car, but unpredictable. So yeah, either my tach is off, which is possible or that inflection curve in the distributor is set wrong, or I'm wrong, I should get a light on there, I think I did a year ago and that was it.. Distributors make it fun (there's one I"ve never heard before)
Just looking at the graph and thinking about it, it should stabilize at the inflection point, maybe I should reduce the rpm and check that timing advances too? mechanical.
The slopes aren't the same, something else to think about.
Today was my last run, possibly of the season, 40k km, 25 M since the engine work, crazy, replaced tires, oil, valve gaskets, new pads in back, oil level gasket... hmm not bad indeed.
Maybe next year...
(didn't mean to thread steal.. but I thought applicable and interesting? and maybe wanted to get off my chest, like car therapy? The patient is always right )
Phil
