Stihl fs250 carb

[heyduke]

Ok, this is a weed whacker, not a chainsaw but, it's an interesting problem. The fs250 is a weedwhacker on 'rhoids and great to use when you have a large area that needs attention. The problem was when it started up for the first time this year it wouldn't even run at half throttle, idled fine but when the throttle was opened it would die. The carb is a weird thing with a snorkle on the fuel pump cover that goes up into the air filter box and appears to suck air into the venturi. There is no low or high adjustment, just a single screw, marked "-Ld+" that looks like an idle speed adjuster, but isn't. It has very fine left handed threads and a blunt end that seems to cover a big hole in the bottom of the venturi, a little behind the choke. The hole looks like its there to let fuel into the venturi, the screw to meter it. Anyway, I spent hours fooling with the carb but nothing worked. This afternoon I took the carb off again so I could take it to the dealer to match with a rebuild kit. I started twisting the little screw, saw it was LH threaded and took it all the way out and then screwed it back in with just a little of the hole covered. It started and kicked butt. Anyone know the skinny on these carbs? It's a stihl branded zama. I've found several mentions of them using google but none that figured out that the "idle speed" screw was a fuel metering needle.

 

[w8ye]

I know the OP has a FS-250 but the MS 250 carb may be close in size and the levers close to the same?

The definitive carb for the 025 and MS-250 chainsaw is the Walbro WT215. They are a conventional twin needle carb. No snorkel or anything.

They only cost $22.50 + tax at my local Stihl dealer.

Edited: To correct the carb number from WT-415 to WT-215

 

[jughead500]

Fs250 not ms250
Yes the fs250 carbs suck.both 250's ive had have been "cold natured" both of mine though have been the fully adjustable carbs.

 

[AKDoug]

The definitive carb for the 025 and MS-250 chainsaw is the Walbro WT415. They are a conventional twin needle carb. No snorkel or anything.

They only cost $22.50 + tax at my local Stihl dealer.

WT215

 

[1Alpha1]

Fs250 not ms250
Yes the fs250 carbs suck.both 250's ive had have been "cold natured" both of mine though have been the fully adjustable carbs.

I have an FS-250R and it runs like a top. Mine has the fully adjustable carb and it has never given me any issues.

 

[sawfun]

I have an fs250 and an ht250, both have H and L adjustments. The Zama carb on the trimmer has not been that great. It doesn't maintain an idle speed consistantly. I rebuilt it and had the dealer check it out but he said it just needed a H side adjustment. Well it is still the same so I guess the real fix is a new carb. But the thing has tons of power and runs well from off idle up. So for now I just blip. The polesaw runs fine and is like a 200t on a stick.

 

[heyduke]

Fs250 not ms250
Yes the fs250 carbs suck.both 250's ive had have been "cold natured" both of mine though have been the fully adjustable carbs.

once figured out, this carb is adjustable, at least for fuel/air mixture. there is no adjustment for idle speed. my local stihl dealer told me, after puzzling over his computer monitor for five minutes, that the fs250 came with nine different carbs. i don't know how this one got so completely out of adjustment. i don't remember fooling with it. adding to the confusion is the fact that its left-handed threaded. you turn it clockwise to enrich. also confusing is that it looks exactly like an idle adjustment screw with a large, slotted head and is adjacent the throttle lever.

 

[heyduke]

I have an fs250 and an ht250, both have H and L adjustments. The Zama carb on the trimmer has not been that great. It doesn't maintain an idle speed consistantly. I rebuilt it and had the dealer check it out but he said it just needed a H side adjustment. Well it is still the same so I guess the real fix is a new carb. But the thing has tons of power and runs well from off idle up. So for now I just blip. The polesaw runs fine and is like a 200t on a stick.

yes, i like this trimmer because it does have, "a ton of power." oddly, this carb has no idle speed adjustment, just a single mixture adjuster. the needle is maybe 1.5mm in diameter and not tapered. the carb casting has places for h and l screws to be located and they are marked. the single mixture adjustment is located where the idle adjustment screw is supposed to be. i'm still scratching my head. i found new fs250 carbs on amazon for around $20 + shipping. they appear to be conventional. for now, i'll stay with this carb. once you understand that the idle adjuster is really a mixture adjuster and you have to turn it backwards, it works well. how many gardeners and landscapers do you think ever managed that?