Old Stihl FS80 Carb Flooding

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!

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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.

Click to expand...

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!

Click to expand...

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.

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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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.

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.

Click to expand...

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.

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.

Click to expand...

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)

Click to expand...

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.

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.

Click to expand...

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.

Click to expand...

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.

Click to expand...

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.

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.

Click to expand...