Stihl trimmer bogs and dies

SlopeMan2

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Nov 15, 2017
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This 7 year old trimmer began bogging down and dying. Figuring it was fuel supply, I installed a new carb., fuel lines, bulb, plug, and it has a LOT of compression. Figured it would be good to go. No ------it just acted the same way. No amount of carb. adjusting can keep it running. The plug looks like it has a little fuel on it. Now, it being a 2 stoke, am wondering if they are susceptible to having leaks at the crankshaft seals. I have been into that with 2 stoke motorcycles. Thanks for comments.

Have been searching for seals for the FS 55 Stihl trimmer. I see a lot of seals, but most of them are for newer models, like FS-80 on up. Does anyone know if others will interchange. Don''t know if that is the problem, but wouldn't hurt to try putting new seals in.
 
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bertsmobile1

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You start at the fuel tank.
If it can not hold 10psi then the carb will not get enough fuel
If it can not vent they you will end up with an air lock.

Unless you bought all of your parts from a real mower shop then there is no reason to believe that they were actually good.

After pressure checking the fuel tank you then pressure test the carb.
Seen brand new ones that leak like a seive.

Then you can think about pressure testing the crank cases.

The usual signs of a leaking crank seal is an engine that requires 100 pulls to start from cold ( seals dry & leaking badly ) tends to run a bit fast & hot ( mix is too lean ) but will start quite normally when hot ( seals wet and not leaking as much ).

Have you removed the muffler and checked the trimmer without it ( very loud )

Starting well then bogging and stalling is a classic symptom of a blocked muffler or exhaust port.
Usually they will start quite fine the idle forever & a day the as soon as they get any load just quit because the engine chokes on its own exhaust.
 

SlopeMan2

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Thanks bertsmobile 1. It was the spark arrestor in the exhaust port stopped up. You hit the nail on the head. The thing was so stopped up, it took awhile to clean it. I had already put a new carb and plug in it, which didn't hurt any thing, but that was not what was keeping it from running. I tweeked the low and high carh adjustments, and runs just as good as new. Thanks a lot. Got LOTS of weed to cut. Has been a great year for weeds, Thanks again.
 
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