When your Ryobi 4-cycle trimmer won't start, the trimmer has so many parts and so many problems that even knowing where to start looking for the problem can feel like a nightmare. But these small engines can be repaired, restoring new life to an otherwise dead trimmer. Nearly any determined owner can accomplish most repairs with a few simple tools and knowledge.
Clean the Trimmer
Too many times, the "it won't start" problem actually starts with a dirty trimmer. The Ryobi trimmer, like humans, needs an adequate air and fuel supply to keep running. If these systems are dirty, the engine will die and won't start up again until they're cleaned. You can use a brush and a rag to clean the area around the air filter and inside the muffler. You can wash the air filter in soapy water or replace it with a new filter, which will solve so many basic problems. You can go even further if you have access to a power washer. Simply drain the fuel tanks and wash all the dirt away; let the trimmer dry overnight before attempting to restart it.
Check the Fuel Flow
If a good thorough cleaning hasn't solved your problem, the next place to look is the fuel supply. Often, if you stored your Ryobi for more than 30 days with fuel still in the tank or carburettor, you'll have to let the gas dry long enough to leave behind a sticky, resinous coating on all the fuel system parts. This gummy layer is like a hardening of the arteries, gradually choking off the supply of blood to the heart of the trimmer. Get rid of any bad gas left in the tank. Rinse out the fuel tank with warm soapy water, and replace the fuel filter and both fuel lines. If the trimmer is still having starting troubles, you'll want to remove, disassemble and clean the carburettor.
Examine the Spark
If the gas system is in good working order, you'll want to look at the spark and the ignition system to see if a spark is getting fired. You'll need to replace your spark plugs on a seasonal basis at a minimum. If your spark plug is new and working just fine, the wires leading up to it may have corroded and lost their efficiency. Examine the spark plug's boot, the lead wire and the short circuit wire to ensure the wires are working properly. If your Ryobi is more than three or four years old, it may be time for a new ignition module. When the ignition module goes, nothing will get your trimmer started again except a new module. Remember though, the spark carried along these wires is a high voltage, so always take extreme care when working on the ignition system as an accident here can be lethal.
If your fuel and ignition systems check out, the trimmer likely has a sufficient air leak somewhere inside the internal parts of the engine. Usually these problems don't occur unless your trimmer has taken some serious punishment. Unfortunately, these problems are difficult to locate and fix, so leave these repairs to a professional.