# Old Stihl FS80 Carb Flooding



## ncbeeman (Mar 27, 2008)

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!


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## scottr (Mar 27, 2008)

ncbeeman said:


> 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!



Hey beeman, my FS80AVR is 22 years old. Do you push the carb overflow button after you prime it 3 or four times?


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## ncbeeman (Mar 27, 2008)

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.


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## scottr (Mar 27, 2008)

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.


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## ncbeeman (Mar 27, 2008)

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.


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## scottr (Mar 27, 2008)

ncbeeman said:


> 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.



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.


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## ncbeeman (Mar 31, 2008)

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.


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## THALL10326 (Apr 5, 2008)

ncbeeman said:


> 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!



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..


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## ncbeeman (Apr 5, 2008)

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.


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## 046 (Apr 5, 2008)

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!


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## pycoed (Jun 14, 2008)

ncbeeman said:


> 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.
> 
> ...



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)


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## ncbeeman (Jun 14, 2008)

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.


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## pycoed (Jun 15, 2008)

ncbeeman said:


> 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.
> 
> ...


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


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## pycoed (Jun 25, 2008)

ncbeeman said:


> 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.
> 
> ...



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.


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## RES (Jul 5, 2008)

I have been told that there is a repair kit available for this TK carburetor from Bantasaw.com in Canada.


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## 00marr (Sep 18, 2008)

pycoed said:


> 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)





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


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## Goball (Jul 12, 2011)

*FS80AV Carb Check Valve and Overflow*



ncbeeman said:


> 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.
> 
> ...



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.


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## ncbeeman (Jul 12, 2011)

Goball said:


> 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.


 
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.


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## Fish (Jul 12, 2011)

Goball said:


> 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.


 
You need to go through the carb and likely replace the needle.


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## Goball (Jul 28, 2011)

ncbeeman said:


> 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.
> 
> ...



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.


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## Hyprdrv (May 10, 2012)

I also have a FS 80 AV Stihl with the KT carberator I believe you guys are refering to here. When I start the motor I notice fuel being sucked back up the vent tube. Is this a related problem to the check valve mentioned above? After priming and using the bottom plunger the motor will start for about 20 seconds then die as if out of fuel. If I slightly press the bottom plunger it may run again for a few seconds. I've replaced all the gaskets and seals but nothing seems to help. It was mentioned to replace the "needle" above. Which needle and does anyone have a diagram or exploded view of the carberator?

Thanks in advance,
Steve


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## Fish (May 10, 2012)

Your trimmer is older than most of the kids here, so I'll tell you what I have done, since Stihl stepped away from this trimmer a decade or two ago.

The needle you are referring to is part of the "Purge" circuit, not a "primer". When they go bad, they will let air suck in and affect the
system. 

The "meatball surgery" fix is to just stick a roofing nail into the end of the line and go on. The choke is sufficient to start the trimmer,
it may take a few extra pulls, but you have little or no alternatives.


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## Goball (May 10, 2012)

*Stihl FS80*



Fish said:


> Your trimmer is older than most of the kids here, so I'll tell you what I have done, since Stihl stepped away from this trimmer a decade or two ago.
> 
> The needle you are referring to is part of the "Purge" circuit, not a "primer". When they go bad, they will let air suck in and affect the
> system.
> ...



Thanks for the advice. I'll have to dig it out of the pile one of these days as I had all but given up on the animal.


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## dbittle (May 10, 2012)

*Same Problem on HT75*

I had this problem on my HT75 polesaw (same powerhead). At the time, (last fall) new Walbro carburetors were going for $50 on ebay. That was the way I went, since the cost difference between the kit and the new carb was $35 or so and lowered the hassle factor. It worked great, so that's a good option.


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## Hyprdrv (May 11, 2012)

Thanks Guys,
I'll try replacing the needle valve and see what happens. If I can find a TK carb I'd go that route. I'll post any results.

Steve


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## dbittle (May 11, 2012)

*Wrong Carburetor...*

It was a Zama carburetor on my Ht-75, not a walbro. My reading on the problem before I just punted and replaced the thing made me think the primer is supposed to pull fresh gas from the tank, fill the carburetor with it, and then return the excess gas to the tank. When the check valve fails, it drips gas when the engine is running. One thing to be careful of is that some of the Zama carbs have a single mixture screw instead of high and low circuit screws. The Zama website has information on what carburetors fit what engines and there is one on ebay right now for $49.95 that has the high and low circuit adjustments. 

David


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## Fish (May 11, 2012)

Hyprdrv said:


> Thanks Guys,
> I'll try replacing the needle valve and see what happens. If I can find a TK carb I'd go that route. I'll post any results.
> 
> Steve



The needle valve has been nla for many, many years, as well as the carb, which is why I suggested just plugging the excess line so that it won't suck air back into the carb.

Or you could check with the local Shindaiwa dealer and see if he can get a carb for the T-25 trimmer which had a similar carb which could be 
made to work on your trimmer, which would be expensive if still available.


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## Fish (May 11, 2012)

Oh yeah, for those that may be confused, there were two totally different fs80 Stihl trimmers, the old one was a Japanese trimmer Stihl put out in the 1980s, that is the one that we are talking about here.


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## Eccentric (May 11, 2012)

Fish said:


> Oh yeah, for those that may be confused, there were two totally different fs80 Stihl trimmers, the old one was a Japanese trimmer Stihl put out in the 1980s, that is the one that we are talking about here.



Yep. I have one of those. My grandpa bought it new in 1984 or so. FS80AVR with electronic ign. No relation at all to the later FS80 trimmers. I have an older (and clapped out) Shindaiwa Green Machine trimmer that has given up a few parts to keep that ancient Stihl/Shinny running over the years. I should have bought the NOS P/C that were on feebay a while ago for $25 or so. Going to have to break down and pick up an FS250 soon. The FS80AVR was a good machine. Heavy, but pretty strong for a 25cc trimmer. That machine would have been much better with 10-15 more cc. I guess that'd be a Shinny BP45. I rebuilt the TK carb on it about 15 years ago. Full kit was still available from Stihl at that time.


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## Fish (May 11, 2012)

I have been selling the he ll out of the full aftermarket kit for the TK, mostly because no one else knows much about it.


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## dozerdan (May 13, 2012)

Fish
When Stihl had the East Coast distributor here in Pa they offered a change over kit for those trimmers. It came with a Walbro, throttle cable, air filter and I think another intake block. I installed a few of them years ago. I have a few local guys that still have them and use them daily. My understanding was that the distributor put those kits together from parts from different Stihl trimmers.
If I get one in the shop I will take some pictures and post them for you.

I Put this one together a few years ago and I still use it once in a while.

Later
Dan


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## Fish (May 13, 2012)

Great, I am sure it is possible, those are/were some well made trimmers...


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## whatscooking (May 16, 2012)

*Think i found the problem on mine.*

i have only run it for for a short time,3\4 tank, but it started second pull after i put the carb back on. I want to try it cold tomorrow and see but i think i got it, at least on mine. What i did, grind down or pull out the check valve, it has a small rubber O ring that has let go and pushed up and the needle valve will not open and let fuel in. Set the needle slightly above level. Plug the puke tube on the outside so it cannot pull air back into the carb. Here is where i found to look to make it run, Pull the top off and pull out the sliding valve and figure out how to unhook the cable by pushing down on it and popping it out easy, raise the needle with the small E clip and finally what i think the problem is, where the throttle cable comes out the top, my little boot was holding fine but everything else leaks everywhere, with the carb off but throttle cable hooked up close the two mixture screws find a rubber hose and push in one end of the throttle throat and hold finger on the other and spray your soap mix you have on the top of the carb then blow and see the bubbles come off of the throttle cable area. First time i left the cable off of the valve and put a bolt in the top rubber on the carb and that is where it started second pull. I ordered a cable and wrapped the old one with black tape and it acts like a new one, idles down and revs up all i want. Watch it not start tomorrow but it did not miss a beat today.


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## mudrat2 (Aug 27, 2019)

Not to open an old thread but put the information here for someone else looking for it.
Valve originally in question is part of what is often called the tickler circuit, used to purge air from the carb and allow fuel from the pressurised tank into the carb.
You can pull the tickler valve out and replace the o-ring. The original o-ring seems to get eaten by ethanol.
Grip the brass pin and pull straight up. I used a small collet chuck used to hold small drill bits.
Replace o-ring and push straight back in.

Carb flooding as originally described is usually caused by the needle valve not seating. Possibly damaged tip, or valve seat.
Valve seat can be repaired as it not in the repair kits I have used, it is brass and easily polished by using a steel tool of correct angle.

Look for missing or damaged spring under the small lever that runs from needle valve to center of carb.


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## president (Aug 27, 2019)

I have an fs 96 ,thats shindiawa built .No current info except an
old IPL on stihls site.Good machine!


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