If you're going to do the "time it by ear" thing, remember that one degree over-advanced from the so called "sweet spot" reduces power by as much as a 5-degree retard from that point. I've documented the same results on Chevy, Ford, Dodge, AMC, and a few other engines during several years of dyno runs. Over-advancing the timing also causes piston ring and piston damage due to detonation. It needs to be done at cruise RPM with the vacuum advance disconnected, and a vacuum gauge should be connected to full manifold vacuum, not the ported vacuum source that connects to the distributor. Adjust the timing for maximum manifold vacuum.
Listening to the engine and tinkering with the timing at idle is a colossal waste of time.
Jerry
