Mixing too much 2-cycle oil with the gas can cause excessive smoke from the leaf blower's engine; follow the guidelines in your owner's manual for mixing the fuel and 2-cycle oil. Most leaf blower engines use a 40:1 ratio of gas to 2-cycle oil. To achieve that mix, add a 3.2-oz bottle of 2-cycle engine oil to 1 gallon of gas.
A dirty air filter also can lead to engine smoke. If the filter prevents the carburetor from getting enough air to create the right fuel/air mixture. A fuel-rich mixture can cause the engine to smoke. Clean the air filter and perform preventive maintenance on the leaf blower to help prevent engine smoking.
Clogged jets inside the carburetor also cause excessive smoking because the carburetor can't mix the right amount of air with fuel. If the engine still smokes after completing preventive maintenance (which includes cleaning the air filter), you may need to rebuild or replace the leaf blower's carburetor.
