Andreas Stihl & Co. is a well-known manufacturer of chainsaws. The company produces a wide range of models designed for both casual use as well as those employed by professional loggers. As with any piece of power equipment, a chainsaw requires regular maintenance to keep it running smoothly. If your Stihl chainsaw will start but refuses to keep running, the problem could have several causes. Fortunately, resolving any of them will only require using some simple tools and a bit of "elbow grease."
Air Filter and Spark Plug
Turn the knob on the carburetor box cover 1/4 turn counterclockwise and remove the cover. The knob is located on the rear of the engine directly above the rear handle.
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Lift off the prefilter and set it aside.
Unscrew the slotted nut holding the main filter until the unit can be freed. Separate the two halves of the main filter. Slip the tip of your screwdriver into the small slot located on one side and gently twist it counterclockwise until the two halves come apart. Once the main filter is removed, you will gain access to the spark plug.
Tap the prefilter and main filter halves to knock loose any accumulated sawdust or dirt. If the filters have become severely clogged, soak them in Stihl brand nonflammable solvent to remove this debris. Set the filters aside to dry.
Remove the spark plug boot and wire from the spark plug. Use the wrench end of your adjustment tool to remove the spark plug by turning it counterclockwise.
Examine the firing tip of the plug. If it has become encrusted with carbon deposits, clean the tip using a brass bristle brush. If the plug tip is severely burned or has not been replaced in 100 hours, buy an identical new plug from your Stihl dealer or any auto parts retailer.
Reinstall the spark plug. Reassemble the main air filter and screw it back into place. Slip the prefiler back into place and reinstall the carburetor box cover.
Start the saw. If it runs smoothly and accelerates properly, you have corrected the problem.
Incorrect Idle Speed
Locate the carburetor adjustment screws. You will find them on the right side of the engine directly above the sprocket cover. The screws will be labeled "H", "L" and "LA."
Start the saw and allow the engine to warm. Remove your finger from the throttle trigger and allow the saw to idle.
Turn the idle speed adjustment screw (LA) clockwise until the chain begins to turn, then turn the screw counterclockwise 1/4 turn.
Recall the last time you mixed fuel for the saw. If it has been more than 30 days, or if the weather has been particularly cold, the fuel may have become contaminated. Ethanol-blended gasoline begins to deteriorate after 30 days.
Empty the fuel tank, pouring the unused portion back into your fuel container. Dispose of the old fuel in accordance with all local environmental regulations.
Purchase fresh unleaded gasoline with the highest octane rating you can find. Stihl recommends purchasing only small amounts of fresh gasoline, which will be used quickly.
Mix the gasoline with Stihl brand 2-cycle engine oil. The gasoline to oil mixing ratio is 50:1. Stihl recommends using its brand of 2-cycle oil as it has been specifically formulated for use in their 2-cycle engines. You can acquire this product from any authorized Stihl dealer.
Refill your saw's fuel tank and start the engine. It should run more smoothly with increased power.