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My Stihl FS 76 trimmer runs ok til it gets warmed up. Then, if I let off the gas for something, when I try to rev it up again it will not. It either falters and does not rev, or it dies. I've replaced the plug and cleaned the air filter. Haven't replaced the fuel filter, but since it runs fine til warmed up, that doesn't seem like the issue (to me). Any ideas?
THANKS
TVZ

Next day--Darn, I thought I might have had an idea--plugged gas cap vent, causing a vacuum in the tank as the gas level goes down, preventing gas from feeding to the carb after running for a while. But I tried loosening it for a second. No improvement---

Looks like 60 folks have viewed this w/out coming up w/ any ideas. A stumper, I guess---

One of my trimmers used to do that it was not a Stihl but same simptons. Took ages to find the problem but on mine the fuel line in the tank was collapsing, not sure why but i replaced the fuel line and it has been fine since.

Bootsy said:

One of my trimmers used to do that it was not a Stihl but same simptons. Took ages to find the problem but on mine the fuel line in the tank was collapsing, not sure why but i replaced the fuel line and it has been fine since.

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Thanks Bootsy. How would I know if that's my problem? I can't open the gas tank and look in there while gunning the engine, can I? Any ideas other than just replacing it?

Hi TVZ, on mine i left the fuel cap off, started it up with it on the ground and ran it till warm, then i looked in the fuel tank (at this point i thought it was a fuel problem and was thinking the fuel filter was getting stuck so some of it was out of the fuel) i pulled on the throttle and saw the petrol pipe collapse about half way down, as soon as it did i could no longer rev it up and it displayed the same problems as yours. I replaced the fuel line and it has been fine since. When i removed the faulty petrol line where it would collapse was soft and spongey unlike the rest of the fuel line.

Bootsy said:

Hi TVZ, on mine i left the fuel cap off, started it up with it on the ground and ran it till warm, then i looked in the fuel tank (at this point i thought it was a fuel problem and was thinking the fuel filter was getting stuck so some of it was out of the fuel) i pulled on the throttle and saw the petrol pipe collapse about half way down, as soon as it did i could no longer rev it up and it displayed the same problems as yours. I replaced the fuel line and it has been fine since. When i removed the faulty petrol line where it would collapse was soft and spongey unlike the rest of the fuel line.

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Thanks Bootsy. One time when I was a kid we were out in a boat and the outboard motor started on fire. As I remember, we concluded that we had left the gas cap off, and that was the cause. I don't really know how that would happen or if that was really the cause, but I've always been very afraid of leaving gas caps off since then!

In view of your bad experiance i am not surprised you dont want to try it, and after thinking about it maybe its not a good idea what i did. What you could do is drain the fuel and check the pipe in the tank. Of course your problem may not be the same as the one I had.

Bootsy said:

In view of your bad experiance i am not surprised you dont want to try it, and after thinking about it maybe its not a good idea what i did. What you could do is drain the fuel and check the pipe in the tank. Of course your problem may not be the same as the one I had.

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Darn, I was hoping you'd convince me that there was really nothing to worry about with your procedure. Maybe I'll be brave and warm it up w/ the cap on; then, w/ fire extinguisher at hand, quickly take off the cap and check the line.

How bout just pulling the fuel line without running it with the cap off and feel the fuel line? Way safer, a lot less messy, and the easy way of doing it?

pile81 said:

How bout just pulling the fuel line without running it with the cap off and feel the fuel line? Way safer, a lot less messy, and the easy way of doing it?

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I'll try that, Pile--Just not sure I'll know just how hard it should feel--but I'll try it---

Well it should be firm and not feel like a piece of gummy bear, and if you tug on it a little it should rebound

On mine the petrol pipe were it would collapse felt soft, if i held the end of the pipe and put it between a couple of fingers then pulled it through them i could feel it had a soft section in it.

pile81 said:

Well it should be firm and not feel like a piece of gummy bear, and if you tug on it a little it should rebound

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Thanks all. I've ordered a new fuel line & filter. Now we'll see if I can get them in place...

I am guessing maybe the fuel tank is not venting or carbon is in the spark screen cause the muffler to be clogged :thumbdown: