The carburettor on a Stihl chainsaw drives the fuel system, while the boot attaches to the spark plug and helps drive the ignition system. Although these two parts are interconnected, removing them requires two different procedures. These parts are crucial for the chainsaw's operation, so only attempt to remove them if you feel confident you can adequately make repairs. Damage to these systems can cause serious internal engine damage if performed improperly. It's best to draw a diagram before removing the parts to help you reassemble and reinstall them later.
Undo the carburettor's box cover on top of the engine by unhooking the clasps or unscrewing the screws, depending on the model. Unscrew the air filter from its mounting plate, which is directly underneath the air filter cover. Lift the air filter free of the Stihl. Remove the baffle, a rubber ring, if fitted around the air filter's mounting posts.
Squeeze the throttle trigger on the rear handle to open the throttle wide. Reach down and disconnect the throttle rod (a metal rod) from the throttle trigger. Unhook the throttle rod from the throttle shaft next to the carburettor. Lift the metal throttle rod out.
Disconnect the two rubber fuel hoses from the intake and outtake valves on the carburettor with your fingers. Unscrew the two mounting bolts holding the carburettor to the intake manifold. Lift the carburettor out and inspect the carburettor. Check the gasket, the rubber seal, underneath the carburettor and replace it if it is cracked or damaged. Leave all carburettor repairs to a qualified mechanic.
Undo the two screws on the underside of the front handle. Pry out the plugs on the clutch side of the handle with a screwdriver. Undo the four screws holding the front handle in place on the engine using a screwdriver. Pry the plastic bumper strip, just beneath the two metal bar posts, out of the engine using the screwdriver to wedge it off. Remove the plug just below the bumper strip. Undo the screw beneath the plug. Pull the front handle off the engine.
Remove the sleeve and the washer that sit above the intake manifold around the two metal stubs where the carburettor sits. Pull the short-circuit ground wire from the contact spring just beside the intake manifold. Pull the short-circuit wire out of the retaining clips.
Push the rubber grommet, with attached wires, sitting just beneath the manifold, into the handle housing area. Squeeze and push the impulse line into the handle housing area. Push the manifold into the handle housing area. Pry the plug out of the annular buffer on the side of the handle. Pop the annular buffer out of the handle housing. Carefully lift the handle housing off the engine.
Pull the rubber boot and wire off the spark plug. Pull the leg spring out of the inside of the boot using the needle-nosed pliers. Unhook the leg spring from the ignition lead on the wire.
Pry the rubber boot off the end of the wire. Cut off the new ignition lead to a length of 175mm. Rub 20mm of the ignition lead with oil. Fit the spark plug boot back onto the end of the ignition wire. Install all parts in reverse sequence.