Ryobi’s line of string trimmers are valuable tools for the homeowner seeking that professional look for their lawn. These small, 2-cycle gas engines are built for lightness and durability. But like all old engines there will come a time when it breaks down. Unlike larger engines, these engines need only fuel, spark and compression to run. Isolating any problem into one of these areas will help make repairing your trimmer faster and get all of the connected parts, which may also be causing problems.
Check for a Spark
Slide the screwdriver underneath the spark plug’s black rubber boot attachment. Pull off the plug gently. Use the socket wrench to remove the spark plug.
Insert a new spark plug into the plug attachment but don’t connect them to the engine. With a gloved hand, hold them next to a metal point on the engine block. This grounds the spark.
Pull out on the starter cord a few times and look for a blue spark across the engine and spark plug. If there’s no spark or the spark comes out a weak yellow continue on with this section’s steps.
Inspect the rubber boot and wire for any damage or loose connections. Follow the electrical wiring all the way back to the ignition module. Make sure the “On/Off” switch is working properly and that the wiring is grounded. Replace any worn parts or wires.
Check the flywheel key, which controls the spark’s timing, for any dents or damage. Replace if necessary. Have a professional mechanic test the magneto gap and starter coil to see if they are holding and firing the necessary charge.
Pull the trimmer off the ground by its starter cord. If the engine drags out the rope, your compression is low. Check every entry and exit point for air flow problems.
Use the screwdriver to remove the air filter and muffler cover. Clean the air filter and spark arrestor screen with the dish detergent and water. Let them dry completely before putting them back into the engine. Replace if they’re too dirty to clean.
Inspect the muffler and exhaust port to make sure they aren’t damaged and are fastened properly to the engine.
Check the bore, piston and cylinder for any cracks or dents. You will likely need to replace the engine if there are.
Fuel System Repairs
Dump out any old fuel and disconnect the fuel line from the carburetor. Pull out the old fuel line and fuel filter from the engine. Replace these with new parts, fill with freshly mixed gas and try starting the trimmer again.
Check the gas tank and engine for any seal problems. Make sure the vent on the gas cap is open and not blocked.
Remove the air filter cover and set the trimmer to half choke. Try starting the trimmer. Wait until it pops, then immediately squirt some starter fluid into the neck of the carburetor.
Start the trimmer again. If it runs for a minute then shuts off, or burns out a lot of thick smoke, you should take it to a professional mechanic to have the carburetor serviced. Make sure they install a carburetor kit.
Things You Will Need
- Leather work gloves
- Socket wrench
- Dish detergent
- Most gas related problems are caused by old gas in the fuel lines and carburetor. Keeping these lines clean, clear and maintained, will reduce the amount of problems for all small engines.
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