Oil and Gas
About tuning a chainsaw. You need to know a couple of simple things. Don't use cheap two cycle oil. Get either Stihl or Husky, and try to find gas without alcohol, as that's a problem causer. In case you don't know, it costs more to produce than gas, but is added to make gas break down in a few months, so people can't store it for long periods. Use Stabil in your saw gas and it will last at least a year.
Set the Carb Rich
The carb has three adjustments. High speed, low speed, and idle speed, which opens the throttle a bit. High speed running too lean burns up most saws that get burned up. Set it rich enough so the saw pops when held wide open and not cutting, but goes into a scream as soon as it is laid on the wood. This rich mix is needed for cooling as evaporation of the gas is what keeps the cylinder from scoring, along with quality oil.
Setting Correct Idle Speed
Do the high speed adjustment first, then the low. The low speed jet should be set to run as rich as the saw will handle without loading up when it idles for a few minutes. If it blows a lot of smoke when you pop the throttle open after a long idle, it is too rich. If you have to jack the trigger a few times to get it to rev up after idling, it is quite a bit too lean. Adjust the idle speed screw so the chain starts to turn while the saw is idling then back off till it just stops. Readjust the low speed screw again. Then go back and readjust the high speed. If the saw won't set and idle smoothly for 15 minutes or even a half hour it isn't going to start well, because it starts on idle, so setting for easy starting is the reason to tinker with the idle jet till it's just right. They are fun to run with you don't have to wear out a starter rope getting it started, and if it will run till you pick it up, if you set it down to move something.
If you have a Poulan or a small Husky made in the last 3 three years, try to find a sucker to buy it for enough money to pick up a professional model Husky or any Stihl. Johnsered are better then either of those two.
Best Bar Length
Don't break your back with a long bar. I run 20 inch for almost everything, but have a huge saw which will run a 60 inch bar, though 36 is the longest one I have and I've never even mounted that one up. A 30 inch will take down a 70 inch tree quite easy, and a 20 inch will drop a 4 foot diameter tree quite handy. I don't care to mess with larger trees unless I have to remove one. When cutting firewood I try to get trees between a foot and 30 inches for easiest handling, and a 20 inch bar takes those on perfectly.
Best chain is semi-chisel. Dealers try to sell chisel, which seems impressive when new, but is hard to sharpen, doesn't stay sharp well, is harder on bars, and doesn't cut as many cords per chain as semi-chisel. Stihl chain is the best you can buy. Oregon is good though and easiest to find. I'm talking about 3/8 inch pitch. If you have a tiny saw, the chain recommendation changes a little.