Saw Adjustment particular to Homelight XL12
First of all take all possible safety precautions and wear ear protectors and remember, saws are very very dangerous!
Back to the XL12 or XL12XL LuckyVision is correct, follow the suggestion and Once you have the 2 mixture screws identified (one is above the other and the same size and in a rubber bush) check also for the idle speed screw it is either a large screw visible from the outside or under the airfilter and its cover on the side of the carb where the throttle rod is connected.
The standard setting of the 2 mixture screws is achieved first by screwing them in until they stop and be VERY VERY careful not to overtighten them as it will distort the carb body and you will need a new carb.
Now unscrew the low mixture needle 1 and a quarter turns and the high mixture needle 1 full turn.
Clamp the saw securely in a metal working vise by its bar and adjust it so the chain can revolve without any danger of fouling the vise or the vibration loosening the vise.
Start the saw and warm it up and then let it idle, if it stalls screw the idle speed screw in a 1/4 turn and try again. once the saw is idling ok check to see if the chain is revolving, if it is, reduce the idle speed by unscrewing the idle speed screw a little until the centrifugal clutch disengages (if it doesn't stop and the engine stalls you need new springs or a new clutch before you go any further).
Now carefulluy screw in the low speed mixture screw until the engine speed rises and then cuts out, just when it cuts out note the position and unscrew the screw a half a turn, check the clutch again and if the chain is not revolving the idle mix is ok for the moment.
Now to the high speed needle screw: be aware that weakening the mix with this screw (screwing in) makes the saw rev higher and making it richer (unscrewing it) reduces the speed.
Rev the saw as high as it will go and carefully adjust the high speed needle screw until the engine 4 strokes (makes a rah rah rhum rhum sound)(The only way to describe it!!!) if you screw it in (clockwise) the engine speed will rise and screwing it out(anticlockwise) makes the engine speed fall. The adjustment would usually be around a quarter of a turn out from the position that it was in before you started adjusting it this time, which makes it 1 and a quarter turns out from fully closed. The saw should now be adjusted correctly.
All the above assumes that the petrol tank is immaculately clean and there is a new filter in the tank and that the fuel pipe is in perfect condition i.e. no kinks, no softening or stickiness from thinners and old age so that it collapses when revving.
If you have any doubts and cannot identify the 4 stroking sound do not keep revving the saw as it may seize, get someone to show you a saw 4 stroking and after you have heard it you will get the idea of the sound.