DIAGNOSIS The engine is not getting enough fuel under load. The carburetor's idle circuit or main jet is likely clogged from old fuel or the low-speed screw needs adjustment.
FIX First, drain all old fuel and refill with fresh 50:1 mix. If problem persists, locate the carburetor adjustment screws. The L screw controls low-speed fuel. With the saw idling, turn the L screw clockwise in 1/8-turn increments until the engine runs smoothly off choke and accepts throttle without dying.
IF THAT DIDN'T WORK The fuel filter in the tank may be clogged. Remove the fuel cap and use a bent wire to hook and lift out the filter. Inspect for debris. Replace if it is dark brown or blocked.
HEADS UP The factory setting for the L screw is typically 1 turn out from fully seated. Use this as a baseline if you turned it too far. Do not adjust the H screw marked for high speed; it is factory-set for emissions.