Stihl FS85 fuel leak revisited

Old 09-17-05, 12:10 PM
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Unhappy Stihl FS85 fuel leak revisited

This is driving me nuts. My secondhand Stihl FS85 carb appears to have a fuel leak. I installed a carb kit, minus the welch plugs, hoping that it was just a bad gasket. The primer bulb and fuel lines were also replaced (figured I might as well since they were only a couple bucks more). No luck. It seems to be dripping from the throttle/butterfly shaft itself. Does this suggest the carb is simply worn out or are my eyes deceiving me?

So here are my symptoms:

1) Fuel leaks from the carb whether the trimmer is 'on' or 'off'
2) Fuel appears to be coming from the bottom half of the carb. The metering gasket is in the vicinity but it appears to be in good shape. Fuel drips from the throttle shaft and a paper towel test shows a significant amount of fuel around the throttle spring.
3) As a test, I pushed the primer bulb until it was basically full and then set the trimmer aside for an hour or so. When I returned, the primer bulb was empty, the top half of the carb was dry, the carb bottom was 'wet' and there were drops of fuel hanging from the throttle.

That suggests that maybe the needle isn't fully-seating itself. But if I bend the needle lever any further, the trimmer runs like a dog.

I'm beginning to wonder if it would be cheaper to just buy a new carb for $40-$50...

Any insights welcome. I'm out of ideas.
Old 09-19-05, 12:13 AM
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Correct, it sounds like the needle isn't seating well. Did you check the seat? You may have to clean the seat for the needle to seal against it.
Old 09-22-05, 03:58 AM
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If the primer bulb empties then i'd say you possibly have the fuel lines crossed. Does this have a remote primer or is it attached directly and integral to the carburetor? In other words, are there two or are there three fuel lines? Not including a fuel tank breather line, that is (if applicable).

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