If the engine spark knocks on regular, the timing is adjusted too early. There is absolutely no reason to run premium gas in an engine with less than 9.5-10:1 compression, and the old stovebolts don't even come close unless there's been a lot of modifications done. Mid-grade gas, maybe, but even then, you're compensaating for a mistake in setting the timing. An engine with heavy carbon deposits in the combustion chamber might be more prone to spark knock, because the carbon is redcuing the combustion chamber volume and/or the glowing carbon is causing pre-igntion which leads to detonation.
In a long series of dyno tests, we found that even one degree of over-advanced timing robs as much power as 5 degrees of retard from the optimum power point. If you're going to make a timing advance mistake, err on the side of not enough, instead of too much!
Jerry
