Stihl FS 55 problems

[Smstavinoha88]

I am a new member and figured I would ask for y'all's help before giving in and bringing my trimmer into a repair shop. I have a stihl fs 55 that is around 3-4 years old. Very moderate use. It ran fine but lately it has been acting up. When you start it up, it runs fine for the first 5 minutes then it just shuts down. After it shuts down it will start up again but usually for no longer than 30 seconds at a time. I have replaced plug and all filters and even went to the extreme of putting a new carb on it. None of this has solved the problem. I'm almost to the point of giving up. Could it be a muffler or kill switch problem? I run the stihl synthetic oil and fresh gas in it.. Any opinions would be greatly appreciated.
Thanks,
Steven

 

[EngineMan]

Its a Stihl so test the coil, if bad replace it.

 

[chance123]

You might want to check your compression. I can't remember now but is the "55" a 2 or 4 stroke? If it is a 2 stroke, clean or remove your fire screen in the muffler. If that screen was clogged, I recommend removing your muffler and check that your exhaust port is clear. I have seen it so clogged with carbon that only a pinhole is visable. Also while the muffler is off, look into the port for the condition of the piston and cylinder wall.

 

[Smstavinoha88]

Thanks for the responses. It is a 2 stroke. I took off the rear cover and removed the exhaust filter/screen and inspected everything for build up and didn't notice anything severe. After putting it back together I fired it up and it ran great wide open and idled flawlessly for about a minute. After that it stalled and was hard to start and didn't even seem like it was trying then it would fire up and run perfect for another minute or so.. Does this sound coil related? If so any tips on how to check coil?

 

[EngineMan]

Disconnect the small wires from the coil and with a multimeter see if you have continuity between the low tension terminal (which is used to switch off the engine) and earth, if you have, replace it. if you do replace it remember the air gap setting for the FS55 is 0.15-0.45mm 0.006-0.02in