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Trimmer won't run FS80

Discussion in 'Mechanic and Repair' started by scottt, Apr 4, 2007.

  1. scottt

    scottt LawnSite Senior Member
    Messages: 269

    My stihl fs80 won't start and gas comes out of the carb and soaks the air filter. I'm not talking about a couple of drops, it seems like it would empty the tank if you kept it tilted. Any ideas?
  2. haybaler

    haybaler LawnSite Senior Member
    from ma
    Messages: 511

    I have a FS80, it's been all problems. I also have a 110R that was fine until they put a new carb on it and it is doing the exact same thing your talking about. I wish I new what it was also.
  3. MowerMedic77

    MowerMedic77 LawnSite Bronze Member
    Messages: 1,164

    The needle valve is stuck open or not closing completely on the seat, could be from debris or the diaphragm could be worn. You will need to tear down the carb and inspect. Get a clean work surface and take your time making sure to keep track of the order you remove items(if you have a digital cam take pics of each step so you can remember how it goes back)
    Good luck post back once you have it open and let us know what you find.
  4. leejp

    leejp LawnSite Member
    Messages: 129

    I'm interested in this as well... I bought a FS 90 AR That cranks and fires but will not continue to run. Spray starting fluid down the carb and I can get it to run for a a few seconds so I think I need a carb rebuild. I can get a kit off fleabay for ~$10. How difficult is this?

    Also I do not have the service manual for this trimmer so I can't see how the carb is mounted. There are a couple of holes that extend down to the motor where I took the air filter off. I assume there are screws that I remove to take the carb off in there somewhere.
  5. lawnboy dan

    lawnboy dan LawnSite Gold Member
    Messages: 3,711

    sthil uses zama carbs which suck . walbro carbs are much better.
  6. leejp

    leejp LawnSite Member
    Messages: 129

    Well... My Stihl FS 90 AR got a Walbro WT 38A on it.
  7. JAX76CJ

    JAX76CJ LawnSite Senior Member
    Messages: 379

    I have the same problem, as far as the leaking fuel goes. My trimmers run fine but just leak fuel from the Carb. I have an FS85RX and a FC100... Both with Zama Carbs. I'm not too bothered by it though, since they run great. They only very slowly leak into the air filter.... Seems speratic as well, it doesn't happen always though.
  8. Jay Ray

    Jay Ray LawnSite Fanatic
    Messages: 6,510

    I put a carb repair kit in an FS80 last December, first time for me on a 2-cycle. It is not as difficult as it might seem, just need a small needle nose or tweezers and pay attention or make sketches on the way apart. I just put in the new needle valve, diaphragm, and associated parts and a gasket or two. There was lots of stuff left in the bag.

    It was getting more and more difficult to start, very annoying. I hung it overhead on hooks one night with the carb down. All the gas poured out thru the carb overnight. I think it was getting too much fuel, made starting difficult. Carb repair kit has kept it starting easy and running good since then. The improvement was like night to day.

    I had thought it was the coil. The carb was only 9 mos. old.

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