Gas leaf blower engines are generally high-performance two-cycle engines. Two-cycle engines give more power for the size over a four-cycle engine, but to do this they use a mixture of gasoline and oil. Therein lies the problem. All of these engines are tuned at the factory using precisely pre-mixed fuel and consequently, they will run absolutely fine the first few times you use them. After that, unless you have access to factory-mixed fuel, you may have to do a bit of tuning and tweaking to keep your leaf blower running at its optimum.
Change the sparkplug before you do anything else. Sparkplugs are inexpensive and should be changed once per year no matter what.
Tie down your leaf blower to a table, bench or a saw horse. Make it tight and firm to limit movement.
Locate the two tuning screws on the side of the leaf blower. One will be labeled "H" for high speed and one will be labeled "L" for low speed. Most of the time they will be near the choke control lever.
Start your leaf blower while it is strapped down and let it idle.
Turn the low-speed screw clockwise 1/4 of a turn if the motor wants to stop or cut out at idle. This will slightly increases the RPMs of the motor. If the motor is racing in idle, turn the screw counterclockwise 1/4 of a turn. You can adjust the idle this way until the blower purrs.
Depress the throttle handle about 3/4 of the way. This is where you will set your high-speed screw.
Turn the screw clockwise to increase RPMs, and this will even out any rough running. If the engine is running fast but sputtering, turn the high-speed screw counterclockwise 1/4 turn, or until the engine smooths out.