I would like to know the fuel mixture for a homelite xl12 chain saw

The recommended fuel mixture is a 50-to-1 ratio of unleaded gasoline and two-cycle engine oil, and the manufacturer recommends the use of a two-cycle oil that contains fuel stabilizer to keep the mixture fresh if you are not using it immediately.

Standard plug gap for a chainsaw 0.5mm

Here are free UT10490 Parts Diagrams you can print:

https://www.jackssmallengines.com/jacks-parts-lookup/manufacturer/green-machine/homelite/chain-saws/xl12-chain-saw-ut-10490

You should run your saw at 25:1

More tips and advice on different makes and model chainsaws here

Regarding the adjustment procedure you generally start your low and high mixture screws at one turn from seat, or slowly turn them in all the way until they bottom out and then back them out one full turn. You will adjust the high speed mixture screw at full throttle and get the median point between too rich (loads up) and too lean (dies out). You will want to do the same thing with the idle mixture screw, just adjust at idle rpm. You will also adjust the low idle mixture screw to give you a smooth transition from idle to throttle up. Once this is obtained, you adjust the third or idle speed screw low enough so the chain does not turn at idle rpm but high enough so the saw doesn't cut off. Hope this gets you going.

Yes you do! The ratio is 50:1 fuel to oil. Be sure to use a modern synthetic saw oil available at home centers, hardware stores, and saw dealers. Be sure to use fresh fuel and mix the two in it's own container. Be sure to shake the container thoroughly each time just before refueling to prevent oil starvation in the engine. Don't make up more than one gallon at a time unless sawing is your business. Hope this helps!

Yes it is very important i would recommend also putting in a new spark plug. Thanks for asking and I hope it helps

40:1 mixture for the fuel:oil ratio.16:1 will cause your saw to barely run(if at all) and if it does, will fog out every mosquito for 4 blocks. You can use any reputable 2-stroke oil, though stay away from outboard engine oil. Get the good stuff that says Stihl, or Husquavarnah, or something like that. Even the Homelite stuff is ok. The oil tank takes regular bar and chain oil.

Turn both screws CW to stops (lightly), then back out each CCW 1-1/2 turns. This should get the engine running if it will. If it does not, check the lower diaphragm on the carburetor for hardness or cracking. You appear to be running on prime only--the carburetor doesn't seem to be pumping in fresh fuel. You may need to do a carburetor clean and re-kit. Check the fuel line condition and the fuel filter in the tank for plugging. Make sure the muffler and air cleaner are not plugged. Once you get the engine to continue running, warm the engine up. Open the throttle and adjust the H needle CW--the engine should start to speed up, but still 4-stroking. The proper setting is 4-stroking, but immediately 2-stroke when cutting. Release the throttle and adjust L needle CW so that the engine runs fairly smoothly, yet will allow the engine to 'follow the throttle'. Set idle speed screw so that the chain stops turning, but the engine continues to run. Hope this helps!