ALW,
Since these saws are piston ported engines, you just double the port timings to get duration. Using this, you will see that the lower port timing numbers given by AV8tor are about half of the duration values that I listed for a stock Homelite.. If you use electronic ignition with some form of advance, you can get away with more radical timing while still retaining a decent idle. Everything is a tradeoff, when you gain something, you lose at the other end.

Dave