Not familar with that saw but I have had smaller XL's. First I would go through the fuel hoses, starting at the filter in the tank. If you have a cracked hose it will suck air and not start or the filter may be plugged up enough to not alow fuel to flow freely.

once you know your getting fuel to the carb. you may have to clean the carb. with carb. cleaner (old gas turns to varnish and plugs the carb up). sometimes you can do it without complete dissassemble. remove the diaphram cover and spray the needle valve and passages. usually the diaphram will be stiff and you will probably have to get the WA, WT number off the carb and get a new diapharm at minimum. rebuild kits usually run around 8 bucks, they cover several different series carb, and you can still get them if you look around.

the two screws are High and LO adjustment screws. usually between 1 to 1 1/2 turns out from seated (lightly seated)(don't crank them in or you will ruin the needle seat.

Other than cleaning the air filter, spark plug, and washing out the combustion chamber with carb cleaner that may do it???? I always prime the carb with carb cleaner when trying to start the saw. This alows the saw to fire and rev up and start sucking the gas from the gas tank. usually takes about 3 times before the saw will run on its own.

Putting carburetor cleaner in the combustion chamber, is not a good thing, because what ever oil residue you have on the cylinder walls will be washed off, and cause your piston, and cylinder to score. That is a No No.
What I suggest, it take something like a syringe, have it full of gas/oil mix, and use it to squirt the gas/oil mix into the throat of the carburetor, to get it to run.
In your case, with the chain saw running for a few minutes, It isn't getting enough fuel. I'd get a rebuild kit, and rebuild the carburetor. Also, how strong is your spark? Something else to look at. If it has points and condenser, you can replace them with an electronic module. This replaces the points and condenser. You can pick them up for around $10.00 to $15.00. Hope this helps. Bruce.

I disagree, I done this for years, and taken several apart,and NEVER had anything but good results. It dissolves and cleans the carbon, dirt, and rust. There is no heat or load and it don't hurt a thing IMO. I have even taken the crank case cover off old susposable worn out trashed ones and washed the rust out, sprayed the top end, primed them with carb. cleaner, and they fired up on the first or second pull. The small amount to time it runs off the carb cleaner which has some lubricating properties don't hurt it at all. Now if you can find enough to fill the tank up, don't put no oil in it, and go weed eat and build up heat and put a load on it it will evenually lock it up due to the parts expanding (but, who would be thoughless enough to do that??). You are IMO better off using carb. cleaner than any ether product which has NO lubricating properties for priming, but again no heat or load so that's why ether don't hurt anthing either IMO.

Pistion scoring IMO is also caused by carbon and dirt (sand) being wiped between the piston and cylinder walls especially if you don't clean the spark plug area on top of the head if it's got fine particles of sand and they fall into the combustion chamber. Naturally with heat and load and no lubricate scoring will occur after minutes of operation (IMO usually take several after the unit get HOT and part start to expand.

Any others have facts on this I would like to hear them. But for me when people throw there dirty plugged up, carbon up weedeater, or lawnmower out on the curb there are people like me lurking and getting another 10 years out of it from nothing more than cleaning it up internally.

What is the (gas mixture) fuel / oil ratio for the XL12?
Thanks so much

Dennis: Using Premium Grade 2-Stroke Oil 50:1 is Optimium . 40:1 If you buy Bargin Store Oil Products. The Days of 32:1 or 16:1 are over lol .