When I got the gauge plugged into the intake manifold, I started the car up and went through the same calibration procedure as before: reduce throttle, fiddle with the idle mixture screw, fiddle with the spark timing, reduce it a little more, etc.
The good news: I was able to get the RPMs down into the idle circuit, which I could tell because adjusting the idle screw caused it to stall and adjusting the GAV did nothing.
The bad news: Vacuum gauge showed continuous oscillation between 15-19. This is with the spark fully advanced and the engine warm.
Based on the
guide posted in the earlier thread, I'm thinking this indicates a burnt valve or loose valve guides – something with a valve. Gauge also showed oscillation when I ran the choke test (engine off, turn over with starter motor). I tried spraying PB blaster into the air intake to try to release a sticky valve, but nothing changed.
Am I correct that we seem to have ruled out everything but the valves?