Depending on the nature of your problem, and how new your trimmer is, you may have a manufacturing defect. But, a string trimmer can also wear out quickly if not properly taken care of. The Homelite String Trimmer should be cleaned and serviced on a regular basis, following the recommended manufacturer's schedule. You should only use freshly mixed fuel and 2-cycle oil in these engines. To isolate other starting problems assign it to one of three systems: spark, compression and fuel.
Premix unleaded gasoline with high-quality 2-stroke engine oil into an approved fuel container. Use a mix ratio of about 40:1.
Depress the rubber primer bulb, usually located by the fuel tank on most Homelites, 10 times. Set the choke to its fully open position.
Try starting the trimmer. If the engine pops, set the choke to half-open position. Start the trimmer, let it die. Set the choke to closed, and start the trimmer. Let it idle for a few minutes before trimming.
Use the screwdriver to remove the four retaining screws on the air filter cover if the trimmer won't start. Remove the air filter. Clean it in warm, soapy water. Allow it to dry thoroughly before replacing it.
Set the choke to the half-open position again. Look at the carburetor through the open air filter slot. Spray a one-second blast of starter fluid into the half-open carburetor neck.
Try starting the trimmer with the air filter off and choke half open. If the trimmer starts and burns off a lot of really thick, white smoke, you should have your carburetor cleaned. There is probably dried, or old gas that was left in the carburetor.
Try starting the trimmer again with the air filter and choke half open. At the moment the trimmer fires the engine, spray a one-second blast of carburetor cleaner into the open neck.
Push down all the way on the throttle and let the engine burn off any residue in the carburetor. Run the engine until the smoke dissipates before trimming.
Dump out all of the gas in the tank into an approved container if the trimmer still won't start. Clean the fuel tank with the rag and brush. Remove and replace the fuel line and fuel filter. Make sure the check valve (the small hole on the underside of the gas tank) is open and unobstructed.
Take out the spark plug and replace with a new one. Set the new spark plug into the rubber plug connector. Hold both of them near a metal point on the engine. Pull on the starter cord and look for a spark across the gap.
Take it to a professional mechanic to check out your ignition system, carburetor and crankcase, if you are still having difficulties.