DIAGNOSIS This is a blocked or missing dust port deflector. The M18 Fuel Sawzall has a built-in dust blow-out port near the blade clamp. If the internal passage is packed with debris, air is redirected outward.
FIX Clear the dust port. Use compressed air to blow through the port from the inside of the tool (requires removing the shoe). Also, clean the area around the blade clamp and the vent slots on the gear case housing.
IF THAT DIDN'T WORK The rubber deflector flap inside the port may be torn or missing. This flap helps direct debris downward. If missing, debris and air flow straight out toward the user.
HEADS UP Always wear safety glasses. This problem is often caused by cutting downward into materials, which allows debris to fall directly into the tool's intake. Be mindful of cutting orientation.