Stihl string trimmer help

justjeepin86

justjeepin86

Well-Known Member
Joined
Jul 9, 2005
Location
Winston-Salem, NC
This really doesn't apply to just Stihl, but here goes.
I picked up a FS 131 from my mil not running. It's a reasonably new unit, but hasn't run in quite a while. I drained the fuel and it didn't smell old. Pulled the carb and cleaned it. The thing won't even fire on ether. It does have spark that i have verified. I get the carb could still be gummed, but why wouldn't it hit with starting fluid? What could i be missing.
 
Did you just wipe out the carb or did you clean it out with carb cleaner?
 
Crack in fuel line, not pulling fuel from the tank?
 
Ether is horrible for a 2 stroke. Could be really dry rings or crank case issues not allowing proper fuel mix transfer. Or like the above all goobered up doing the same. Since I am not entirely in the know does the unit rely on a reed valve of sorts? How does the compression feel in the plug hole? Unseated rings from dry or sticky mess and poor compression want help any.
 
grapehead said:
Did you check for spark?
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yes
jeepinmatt said:
Crack in fuel line, not pulling fuel from the tank?
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valid, but they look great and are still quite flexible
shawn said:
Been running Stihl two stroke oil and clogged up the spark arrestor.
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Can't answer there, but he never treated things like they should be.
WARRIORWELDING said:
Ether is horrible for a 2 stroke. Could be really dry rings or crank case issues not allowing proper fuel mix transfer. Or like the above all goobered up doing the same. Since I am not entirely in the know does the unit rely on a reed valve of sorts? How does the compression feel in the plug hole? Unseated rings from dry or sticky mess and poor compression want help any.
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I know, just trying to verify fire. That's it. Not run it.

This trimmer doesn't have, i bet, 20 hrs on it. It's very tight and new.

If it would fire, i will probably buy a new stihl carb. Only 60 bucks.
 
justjeepin86 said:
The carb doesn't even need to do anything.
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well it needs to balance the air and fuel mixture…an engine won’t run on pure gas (or ether) without proper air
 
Does it have GOOD spark? Did you replace the plug? If it's been sitting then even a rebuild kit for the carb may not be enough. Just cleaning it is no good. Bad gas coats all internals and eats into the metal of the carb. Just get a new one, not the chinese version, a $40 one. BUT Ether should make it fire now. You're missing something. The valves on the 4 strokes suck, but with fire it should still run on ether.
 
Pull the muffler off and then try to start it. I've had several small engines do the same and it's some dirt dobber or similar junk in the exhaust that creates too much back pressure. If it starts up then you know to just clean out the muffler
 
R Q said:
Does it have GOOD spark? Did you replace the plug? If it's been sitting then even a rebuild kit for the carb may not be enough. Just cleaning it is no good. Bad gas coats all internals and eats into the metal of the carb. Just get a new one, not the chinese version, a $40 one. BUT Ether should make it fire now. You're missing something. The valves on the 4 strokes suck, but with fire it should still run on ether.
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Well, I saw it pretty good in the daylight, but I'll grab a plug as well. Yeah, I think I'll get a carb regardless. It's a 2 stroke, but might be a 4 mix like @lbyota85 said. Thanks for the answer on the ether. You are only one that has answered that question.

Clubbs said:
Pull the muffler off and then try to start it. I've had several small engines do the same and it's some dirt dobber or similar junk in the exhaust that creates too much back pressure. If it starts up then you know to just clean out the muffler
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I can go down that road too, but this has a large screen for the muffler and I can see that nothing has built in it.


I'm gonna start with a brand new carb and throw a plug in it. I know I have to bite the bullet with that anyway. I'll go from there.
 
shawn said:
Been running Stihl two stroke oil and clogged up the spark arrestor.
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This is pretty common, pull the screen off the muffler and burn off the crud, you can try and run it with out (screen is spark arrester)

Also ether in a 2 stroke will kill it, can happen on first pull, ether is too violent for them.

If you messed with any of the screws on the carb none need to be tight seated, they are tapered, over tightening will destroy the seats and flood they are metering screws for high and low speed. 1.5 turns from lightly seated the adjust as needed once running.
 
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Definitely a 4-mix mill (uses 2-stroke mix, but has valves)...
No help on the no start... my FS131 (going on 4th year) has been 100% trouble free.
Absolutely LOVE the 4-mix, can sling 24" diameter of string thru tall (non-woody) brush and won't bog like a 2stroke... a fawking torque BEAST!
 
Bumping this back up.

I bought a new Stihl carb and put in a new plug. It started immediately. I've ran it some, but it has a miss. I've watched several videos on tuning the high and low, but can't seem to get it better.

Any tips @R Q
 
Something I didn't see mentioned reading back thru is the air filter. Any chance it has deteriorated and clogged the intake?


Simplest fix is to put it here:
Screenshot_20230319-115905_Chrome.jpg


And get one of these:
;)
 
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Just take it to Forsyth mower across from the shit plant on Griffith Rd. $60 and it'll run like a top

#paytheman
 
justjeepin86 said:
Bumping this back up.

I bought a new Stihl carb and put in a new plug. It started immediately. I've ran it some, but it has a miss. I've watched several videos on tuning the high and low, but can't seem to get it better.

Any tips @R Q
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It might be those pesky valves needing adjustment. That's why I don't run those 4 mix units. There are vids on Youtube on how to do them. So when I have issues with a 2 cycle unit, I will change fuel filter, fuel lines if they are at all suspect, spark plug, and either rebuild or replace carb. If I take the muffler off to check the screen, it somehow dissappears. :laughing: Other than that the only other thing I can think of would be corrosion or oil on the "flywheel" which is causing the coil to not create good spark. You have to dissassemble a lot to get to it and then sand it down to remove corrosion. And hopefully the coil is good. Partstree has great parts breakdowns so you can see every part in exploded view and figure out how to get to what you need.
That's all I got. Good luck!
 
justjeepin86 said:
Geez, just take the easy way out. I may, but that's not gonna help me fix the next one...
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The older I get... The more value I see in letting it be someone else's problem

$60x3 is still less than what I value an hour of my time at 🤷🏿‍♂️
 
justjeepin86 said:
Everything I've read said it was ok to tune it without the air filter. So that is what I've done.
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Should be, but air filter affects vacuum, which helps draw fuel.
 
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