Spark

• The spark needs a proper voltage spark, so first check to see if it's even making it to the plug. Disconnect the high tension lead wire's rubber boot from the end of the spark plug. Remove the plug from the engine and replace it. Put the new plug into the boot but not into the engine. Set your Weed Eater onto the ground and find a metal spot near the spark plug that runs all the way into the ground uninterrupted. Wear leather gloves and hold the tip of the plug about 2 cm away from the metal point. Hold the engine with your foot or have a friend help you and crank on the starter rope. If you see a blue spark, you can rule out spark as your problem. If you see a yellow spark, the ignition module will soon need replacing. If you see no spark, this usually signals bad wiring somewhere within the ignition circuit, which you must find and replace to get the spark firing again. Take extra caution when disassembling the ignition system as electrocution can occur.
  
  

Fuel

• Loosen the fuel cap and run the trimmer to see if this solves your problem. Often running problems, especially when the engine overheats, will result in vapor locking the carburetor, which will shut the engine down. Loosening the fuel cap will help some of those gases vent and if this helps your problem, look for what area in the fuel system is getting clogged. The tank has a vent hole in the cap you'll want to check. Also replace the fuel filter and clean the tank to see if any dirt is blocking fuel from entering the carburetor.
  
  

Carburetor

• Remove the air filter and open the choke to its halfway setting. Set the engine on the ground and start it up. Have a friend help you squirt a blast of starter fluid into the open neck when it fires up. If it fires and runs, service your carburetor in a few weeks. If it fires up and then dies, repeat the same steps with a carburetor cleaner, but you'll still need a carburetor cleaning soon. If it doesn't fire at all, you may need a new carburetor or carb kit installed onto your old carburetor.
  
  

Compression

• Compression creates the necessary pressure to spin the crankcase, so if you're losing compression, you'll either lose serious power or won't get the engine started at all. Hook up a compression gauge, which looks a lot like a tire gauge, to the empty spark plug hole in the cylinder. Crank on the starter rope and check your compression reading to see if it's falling down. Your reading should hold steady for at least one minute; if it isn't, search for the source of your air leak.