[jclark003]

Mercruiser 502's of that era have the knock sensors wired in as a separate component to the ignition module. Pretty sure Crusader does it the same way. The knock sensor rolls back the timing curve when it detects engine knock or misfiring. pretty sure you can rewire the harness that runs between the coil and ignition amplifier to bypass.

ive seen those knock sensors throw the best of mechanics for a loop. Once had a minor engine miss that caused a drive plate harmonic. Nothing you could hear but the knock sensor picked it up and would roll the timing back, making the problem worse until it wouldn't even run. Found it only because we threw in an old ignition amplifier that bypassed the knock sensor and the problem went away.

IMO I wouldn't push the timing. It's not going to give you much in the way of performance or economy and in a boat it's very difficult to hear detonation. There is a reason the factory set it where it is.