Not sure what you mean by 'restoring' an old saw. I have lots of old saws and none have ever been restored. Just maintained and used for years and years, eventually they get old. Not much to go wrong with a saw if you use it properly and fix issues as they occur. The absolute biggest killer of saws (or any piece of equipment) is HEAT. Chainsaws can generate tons of heat if you run them dull. I prefer keeping my saws sharp, but many people seem to think it's perfectly ok to keep running a dull saw until they just can't physically push it through a log any more. Saws used like this you might as well throw them away after a couple years.
If the only problem with the saw is an idle issue, then just fix it. Not a big deal to figure out why it's lean. Most obvious is a carb adjustment, plugged jet or a cracked fuel line. But if the saw was abused for years and the crank seals are cooked (from running the saw dull), then at that point you probably need to replace it.