ArboristSite.com Sponsors
 
 


Old Stihl FS80 Carb Flooding

Discussion in 'Chainsaw' started by ncbeeman, Mar 27, 2008.

  1. ncbeeman

    ncbeeman ArboristSite Lurker

    Joined:
    Mar 25, 2008
    Messages:
    13
    Likes Received:
    1
    Location:
    Central NC
    I have an old FS80, the real old one, all orange body with primer bulb on the gas tank. It is floods like crazy, very tricky to start. I just put rebuilt the carb, didn't seem to help. When I say floods, I took the carb off after an attempt to crank it and gas ran out of the intake port. Air filter gets soaked too. The plug has a good spark, (new plug).

    Anyone have any tricks to fix or techniques on starting? It runs OK when it cranks so I hate to get rid of it, but it's becoming a problem!
    Thanks!
     
  2. scottr

    scottr Addicted to ArboristSite

    Joined:
    Nov 18, 2003
    Messages:
    1,965
    Likes Received:
    163
    Location:
    Alabama
    Hey beeman, my FS80AVR is 22 years old. Do you push the carb overflow button after you prime it 3 or four times?
     
  3. ncbeeman

    ncbeeman ArboristSite Lurker

    Joined:
    Mar 25, 2008
    Messages:
    13
    Likes Received:
    1
    Location:
    Central NC
    Scott,
    I have not seen that it helps, what is your procedure for priming? For me, if I pump it one time too many, gas goes everywhere. Made me wonder if it was a mechanical problem or user error.
     
  4. scottr

    scottr Addicted to ArboristSite

    Joined:
    Nov 18, 2003
    Messages:
    1,965
    Likes Received:
    163
    Location:
    Alabama
    A couple of years ago the primer bulb was as hard as a rock and the dealer didn't have one and wanted $7.50 shipping plus cost so I installed a walbro primer bulb. Now I prime to get gas to the carb and then choke it and crank it.
     
  5. ncbeeman

    ncbeeman ArboristSite Lurker

    Joined:
    Mar 25, 2008
    Messages:
    13
    Likes Received:
    1
    Location:
    Central NC
    More info: last night I left the plug out to dry out the cylinder. Gas had dripped all down under the carb, the air filter was wet and gas was standing in the air intake. It's like the carb is siphonening gas out of the tank (uphill?)

    It appeared to have dripped from the relief on the bottom of the carb. This is an old problem, it could drain a half tank of gas in a week or so.
     
  6. scottr

    scottr Addicted to ArboristSite

    Joined:
    Nov 18, 2003
    Messages:
    1,965
    Likes Received:
    163
    Location:
    Alabama
    Mine has never done that. It sounds like there would have to be pressure in the tank to force the gas up to the carb. The gas cap looks like a vented cap, also the short hose from the carb that runs back near the primer bulb must be a vent. The only gas leak that I've experienced is when the fuel line comes loose from the tank.
     
  7. ncbeeman

    ncbeeman ArboristSite Lurker

    Joined:
    Mar 25, 2008
    Messages:
    13
    Likes Received:
    1
    Location:
    Central NC
    To close the loop, my local dealer/repair guy said these old slide carbs have a check valve in them that dies after a while. The carb doesn't seal properly, and when primed they either flood or pull air by this valve and won't prime at all. A sure sign is if the carb makes the engine bog down when the throttle is opened. This valve is not repair-able, you can see one end when you pull the carb apart and look where the needle valve is.

    Hope this helps someone in the future.
     
  8. THALL10326

    THALL10326 The Champ

    Joined:
    Mar 6, 2004
    Messages:
    20,470
    Likes Received:
    1,886
    Location:
    ..
    Welp you got a carb you may not be able to fix. I checked and Stihl doesn't offer a carb kit for that carb anymore, all parts for it are sold as each. A new carb for that unit lists for 141.50, part number 4112-120-0611. Considering how heavy that unit is and how old that unit is it may be a good time to replace it..
     
  9. ncbeeman

    ncbeeman ArboristSite Lurker

    Joined:
    Mar 25, 2008
    Messages:
    13
    Likes Received:
    1
    Location:
    Central NC
    Thanks for the advice. I spent yesterday dealing with this, and have it fixed (temporarily at least). You can actually pull out the check valve and plug the overflow from the carb. This allows you to pump gas straight into the carb instead of having to worry about the check valve. Trick is, don't pump too much or the thing will flood, nothing to stop it since the overflow is blocked.

    There is a carb rebuild kit available, from an after-market. I put the new gaskets and diaphragm in, new needle valve. Spent $25 in labor, $10 in parts and it runs like new.

    No guarantee on how long, but I'm not flush with cash so I'm happy for the time being.

    If i had pictures I would post them, but the repair tech really didn't want to let me in on the secret. I kind of worked it out of him.
     
    scottr likes this.
  10. 046

    046 Addicted to ArboristSite

    Joined:
    Apr 8, 2004
    Messages:
    4,442
    Likes Received:
    278
    Location:
    Oklahoma
    rarely ever need to prime my FS80... choke a bit, then it starts right up.

    glad you got yours going... FS80 has been a rugged trimmer!
     
  11. pycoed

    pycoed New Member

    Joined:
    Jun 14, 2008
    Messages:
    3
    Likes Received:
    0
    Location:
    Wales
    Hi - please post source of carb kit for the old FS80 & a few more details on removing the check valve. I have exactly the same issue as you had ( carb bogging when given the gun)
     
  12. ncbeeman

    ncbeeman ArboristSite Lurker

    Joined:
    Mar 25, 2008
    Messages:
    13
    Likes Received:
    1
    Location:
    Central NC
    I wish I had saved the rebuild kit package, I don't know the part number. It was a generic rebuild kit that fit the carb. Two Stihl dealers knew of the right kit, so I assumed it was commonly available.

    To remove the check valve, you take the diaphragm off (4 screws with the little plastic spring plunger underneath). Inside of that, you see a brass colored pin coming out of the carb. That little plastic spring plunger you push on the outside moves the check valve on the inside. Take some needle-nose pliers and pull this brass plunger out. That is the check valve.

    Now, take a small piece of fuel line and a screw. Remove the overflow line from this part of the carb, the line that drains down the outside at the push bulb. Plug one end of the fuel line with the screw, push the other on the overflow. This prevents gas from flowing out of the carb when you prime it.

    When I crank it now, I just prime it until the line fills with gas, and pull. If it won't crank after a couple of pulls, I hit the primer bulb a couple of times. Keep alternating this until it starts.

    I don't use the choke anymore either, FYI.
     
  13. pycoed

    pycoed New Member

    Joined:
    Jun 14, 2008
    Messages:
    3
    Likes Received:
    0
    Location:
    Wales
    Great info - I was wondering about that little plunger - I've even stripped the carb & boiled it as well as soaked in carb cleaner, but still the same trouble. I'll try removing it all together as you suggest
     
  14. pycoed

    pycoed New Member

    Joined:
    Jun 14, 2008
    Messages:
    3
    Likes Received:
    0
    Location:
    Wales
    Many thanks for this tip - my FS80 now revs as it should!
    I couldn't pull the plunger out tho' - I had to mount the carb in a drill press & carefully drill out the check valve. After I'd drilled about 1/8" I managed to pull the centre plunger out & then I carried on drilling to remove the last bits of brass, releasing the spring & a soft seal of some sort. Easy enough to do if you have a bench drill or mill.
    Thanks again.
     
  15. RES

    RES ArboristSite Operative

    Joined:
    Nov 28, 2005
    Messages:
    414
    Likes Received:
    49
    Location:
    connecticut
    I have been told that there is a repair kit available for this TK carburetor from Bantasaw.com in Canada.
     
  16. 00marr

    00marr New Member

    Joined:
    Sep 18, 2008
    Messages:
    1
    Likes Received:
    0
    Location:
    test


    Carb kits for TK carbs
    http://tewarehouse.com/Catalog/75-1
     
  17. Goball

    Goball ArboristSite Operative

    Joined:
    Jun 2, 2010
    Messages:
    126
    Likes Received:
    13
    Location:
    Sherwood Park, Alberta, Canada
    FS80AV Carb Check Valve and Overflow

    Good info. Just have one question. If I understand your instruction, you simply remove the check valve assy and plug the overflow line from the carb. If plugging the overflow solves the problem, why is it necessary to remove the check valve assuming the check valve port is connected directly to the overflow port? That being the case, maybe removal of the check valve adds no value to problem solution? Hope this makes sense. I plugged the overflow line but the flooding problem still persists. Thx.
     
  18. ncbeeman

    ncbeeman ArboristSite Lurker

    Joined:
    Mar 25, 2008
    Messages:
    13
    Likes Received:
    1
    Location:
    Central NC
    Don't know about the check valve, the guy didn't get into the details. I think it has to do with how the carb primes itself when you pump the push bulb.
     
  19. Fish

    Fish Account Hold

    Joined:
    Apr 22, 2001
    Messages:
    13,971
    Likes Received:
    1,262
    Location:
    Loretto/Manton Ky.
    You need to go through the carb and likely replace the needle.
     
  20. Goball

    Goball ArboristSite Operative

    Joined:
    Jun 2, 2010
    Messages:
    126
    Likes Received:
    13
    Location:
    Sherwood Park, Alberta, Canada
    Hi, I'm having headaches too. Removed the check valve and actually plugged the brass cylinder of the check valve so gas couldn't pass thru it. Your instructions above suggest that there is an overflow connection as well as a primer connection. I only see one connection on the side of th carb which I had assumed to be the primer inlet. Maybe that the overflow (which I have also plugged with a bit of line and screw as you suggest. It still floods like heck. Any more suggestions? Thanks.
     

Share This Page