A leaf blower should never start smoking when in operation. If smoking occurs, stop the engine immediately and identify and solve the problem before using the leaf blower again. Smoke may indicate a serious engine problem which can cause your engine's piston and crankcase to blow out, ruining the engine.
Improper Fuel Mixture
A common, simple problem that may cause a leaf blower to smoke is improperly mixed fuel. Gas leaf blowers use a pre-mixed fuel that combines gasoline with a two-stroke engine oil. These two are combined at a ratio according to the manufacturer's specifications. However, if the fuel mixture is improperly mixed, the fuel will burn poorly inside the cylinder, which may cause the engine to smoke. Dump out any old or poorly mixed gas and remix a fresh batch of fuel, following the mixing instructions closely.
As the leaf blower engine heats up, heated gasses need to vent out of the engine for it to keep running. These vented gasses go through the exhaust port and muffler, and a small layer of carbon will gradually build up along the muffler walls and exhaust port as the gases leave the engine. Take the cover off the muffler and unscrew the spark arrestor screen. If these components are covered in black carbon deposits clean them with a heavy brush and a mild detergent.
The fuel system needs an airtight seal to keep the fuel flowing into the cylinder. If an air leak develops somewhere around the carburetor a small amount of fuel can drip out of the system. If this fuel hits the heated engine it may begin smoking near the carburetor. Usually these leaks occur around the fuel hoses and elbow connectors on the carburetor. Another common leaking site to check is the gasket above the intake manifold.
Other sealing problems inside the engine can also cause the engine to start smoking. These problems generally occur around the seals on both sides of the crankcase. When this happens a small amount of fuel may enter the crankcase and burn up inside. Fixing this problem requires splitting the crankcase into its two separate halves and replacing the seals on both sides. You may also need to check the rings and seals on the piston and cylinder for leaks as well.