How to Troubleshoot the Stihl MS 250

Squeeze the throttle on the Stihl MS 250 and slide the control lever so the choke moves into the "closed" position. Slide the knob on the carburetor cover to the left 90 degrees. Take the carburetor cover off the top of the engine.

Pull the air filter off its mount in the housing area. Pull the shutter, behind the filter, away from the engine. Brush off the air filter, the carburetor cover and the area around the carburetor.

Slide the rubber boot off the tip of the spark plug. Unscrew the spark plug with the socket wrench and remove it. Check the tip of the plug to make sure it isn't broken, bent or blackened. Replace the spark plug, if necessary.

Connect the ignition tester to the rubber boot and to the tip of the spark plug. Set your right foot into the rear handle and put your left hand on top of the front handle.

Make sure the chain saw chain won't hit anything if it starts accidentally. Pull quickly on the starter rope at least four times and check for a spark in the tester's window. If no spark is visible, the ignition system needs servicing.

Disconnect the ignition tester from the boot and plug. Unscrew the spark plug again. Fit the compression gauge into the spark plug hole and tighten it until it's finger tight. Pull on the starter rope again firmly until the compression reading stops increasing. Service the air and compression systems if the reading is below 100 psi.

Unscrew the choke cover plate from the top of the carburetor, underneath where the air filter sits. Disconnect the two fuel hoses from the carburetor with your fingers. Lift the saw and tilt to see if any fuel comes out of the hoses. Service the fuel system if fuel doesn't leak out.