Stihl FS-90 user manual

1. Ensure the Stihl FS90R string trimmer is turned off and allow it to cool if it was recently used. It’s essential to make sure your safety when working with this tool.
2. Disconnect the spark plug by removing the rubber boot from the tip of the spark plug to ensure that the trimmer doesn't start up by accident while working on it.
3. Put on a pair of gloves to protect your hands from the sharp trimmer line.
4. Secure the Stihl FS90R in a vice or similar clamping tool to keep it steady.
5. To prevent the gearbox from turning, insert a screwdriver into the hole located on the gearbox's collar. Rotate the trimmer head until the screwdriver fits into the guide hole behind it.
6. To unscrew the mowing head, turn it clockwise as you look down at the head. This may seem backward but the thread on the screw is reversed to ensure it stays tightened during use.
7. Once you've fully unscrewed the old head, set it aside. You're now ready to install the new head.
8. Place the new head on the spindle and rotate counterclockwise until tightened.
9. Remove the screwdriver from the gearbox.
10. Replace the spark plug boot.
11. Verify that the new head is secure before restarting the trimmer. Begin slowly to ensure that everything is functioning correctly.
Remember that regular maintenance of your string trimmer will ensure it operates efficiently and lasts longer. Always keep safety in mind when working on your equipment.

The Stihl FS 90 uses a .095 inch diameter string.

The fuel mixture for a Stihl FS 90 is a 50:1 ratio of gasoline to Stihl 2-cycle oil.

The Stihl FS 90 is a 2-stroke engine.