OT Stihl cord trimmer

Dave H (MI) · Jul 22, 2021

I have a Stihl FS74 that had a bad primer bulb. Just got around to replacing it after it sat for a couple years. It had no gas in it during that time. It starts right up but after idling for a bit it just stalls suddenly. The more times I start it, the quicker it stalls. After 3-5 starts it stalls right after starting. I don't throttle it up at all. Just want to see if it will keep running at idle. Is this normal or should I be looking into it further. I was able to use it some, but when I let it go back to idle it stalled right away. Not familiar with these...sort of testing the waters. Appreciate any guidance.

quefan · Jul 22, 2021

I would check the spark arrester on the muffler exit. Cleaning mine cleared up issues that were similar.
Heat the metal screen to bright orange and brush clean with wire brush.

pcsaw · Jul 22, 2021

Try running some sea foam thru it

Steve@Advance · Jul 22, 2021

If it is old enough for the primer bulb to fail, chances are the fuel lines are also getting bad and should be replaced. Replace them with the factory hoses. Replace or wash out the fuel filter.

And inside the carb, the metering diaphragm, (the one that operates the needle valve), it gets old and brittle. It should be replaced even if not leaking. It must be soft and pliable to work properly.

docmirror · Jul 22, 2021

The small passages in the carb are clogged. There's no saving it. Go on ebay or Amazon and type in 'FS74 carb'. You'll see a lot of options. Just replace it, and save yourself hours of wasted time.

It'll come with a new primer bulb, fuel filter, and maybe spark plug. Around $20 or less. I just did my FS-45 last week, runs like new.

Russ from MN · Jul 22, 2021

I would try some Seafoam, I've had it clean out carburetors like that. Don't expect it to work right away. If you can adjust the carburetor do so, but once it's cleaned out you may have to set it back.

MarkB_MI · Jul 23, 2021

It's either the fuel lines or the carburetor. Probably both. OEM carbs aren't that expensive, and most outdoor power equipment shops sell good replacement fuel line by the inch.

DoubleR · Jul 23, 2021

I've had trouble with the screen in the muffler plugging up on my Stihl equipment. My Stihl trimmer has been barely running for me, its close to 20 years old. Took that screen out a couple days ago and cleaned it and drilled some holes in it. Runs like it should now. I had the same problem with my Stihl blower and chain saw and did the same thing to them and it corrected my problem.

M-MAN · Jul 23, 2021

When my son in laws did that I cranked it up and scraped the muffler screen with a long nail. It blew the crap off and ran like new again.

RodinNS · Jul 23, 2021

I'd certainly check the filter and lines as well as the spark arrestor as that's all simple enough. What troubles me is that it gets worse as it warms up. That's suggesting to me that there may be a vacuum leak between the carb and engine or bad crank seals. I'd try some carb cleaner through it or seafoam and adjust the Jets if they have adjustment to see if you can make it richer. That may compensate for whatever problem is happening.

Rod

OT Stihl cord trimmer

Dave H (MI)

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quefan

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pcsaw

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Steve@Advance

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docmirror

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Russ from MN

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MarkB_MI

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DoubleR

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M-MAN

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RodinNS

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