Stihl FS 81 no spark!

Could be the kill switch, or a short along the wire from coil to kill switch. I'd also make sure the plug wire, boot, and connection at the plug are in good condition. If the boot or the wire insulation is split then the spark could be leaking out and jumping to ground without going through the plug.

The kill switch is the switch you use to turn it off when you're done using it.

If the plug wire's insulation is bad, then the whole plug wire should be replaced. I haven't worked on an FS81, so I don't know how easy it is to replace the wire on that coil.

If it's a torn boot or the spring connector inside the boot, those can be replaced separately while keeping the same wire.

The kill wire goes from the coil to the switch then from the switch to ground or if the switch is grounded there will only be one wire. They can get rubbed through or cracked and short to ground and give intermittent spark. If you are getting any spark at all I would look at wires before coil. Coils will usually either go bad and never spark or quit when they get hot.

When plug wire is cracked, I've had success by: pulling boot off the circular plug connector, slide heat shrink electrical tape over plug wire, shrink it, put boot back on.

To replace, you can check for aftermarket coil packs - search Stihl trimmer ignition on fleabay. Find yours.

Replace "coil". No, you don't replace spark plug wire. If inner wire is fine and outside insulation is cracked - you can re-insulate with heat shrink tubing. Although you can cut plug wire, attach another piece (inner wires crimped) and insulate - that will work.

Media cat shows 2 different part #'s for the coil and the lead. I would bet the lead unscrews from the coil.

Maybe plug wire does unscrew from coil. Most of the newer trimmer coils I've seen have plug wire molded into coil.

It shows 2 coils. part #'s 4126 400 1301 and # 4126 400 1300 a grommet #0000 989 1010 and an Ignition lead with a length of 175mm. Both coils shown have removable leads.