What I do is static time the engine at TDC "U|C" on the flywheel with the Octane Selector set to zero. Then I dial in 5 deg with the octane selector and take it for a ride. That way I can see how many degrees advance I'm running at a glance -- well, a squint anyway. My problem with using a plain ol' timing light is that I can't get the idle down to 450 RPM which is theoretically just below where the mechanical advance starts.
Too much advance will produce pre-ignition that sounds like pinging and is when the flame travel is normal but is lit off too soon. It generally is not too harmful but robs power and fuel economy and is otherwise undesirable. It can happen at relatively light throttle, if say the vacuum advance doesn't retard soon enough (too weak a spring, some of them have springs that can be shimmed more or less). Recent repops at all crimped together and not adjustable. There is a spec for how much advance at what vacuum.
Detonation on the other hand is when the whole intake charge goes of all at once. This is a really bad deal and burns or knocks holes in pistons, breaks spark-plug insulators, hammers connecting rod bearings and is to be avoided at all costs. Most often it happens at full throttle or close to it. Often one can't hear it because of other engine noise like exhaust, intake "honk" from the carburetor, gear noise, wind and the like. Lean mixture is often a cause, along with excessive heat often caused by lean mixture. Airplane engines have exhaust gas temperature gauges to prevent this sort of thing and pilots are trained to watch the gauges. Red hot carbon deposits can also cause this; also spark plugs that are too hot a heat range, which can act like glow plugs in model airplane engines. Typically these problems aren't common in production auto and truck engines but when one starts raising the compression ratio it can be a problem with low-grade fuel.
