>>>*Ignition timing (or spark lead) sets off the mixture ahead of time. The reason is it does take time for the fuel to burn, so a head start is required.

Too much head start and it pings, or even worse, detonates. Pinging sounds like a can of marbles in there, detonation is that loud noise and big cloud of smoke we don't want.

If the spark lead is too late, the fuel is still burning as it goes out the tailpipe which does nothing but waste it.

There is only one proper advance amount, no power can be gained by adding more than needed. This is a common mistake because a bit too much advance makes an engine feel nice and snappy running free.

But under load...??? less power.

Retarding slightly, in one degree movements until the engine just stops pinging is one way to find the right amount. But normally the factory setting will be correct in ALL cases assuming all else is normal.

Sorry for the short lecture, couldn't help myself...*LOL**...*EB