Stihl MS 250 shutting down

[Pioneer]

If you let it cool right down and then start it up will it run fine for a couple of minutes again? If so suspect the coil, a coil on its way out will perform erratically when it gets heat soaked. This can give you a false indication like the saw is out of tune.
I just went through this with a Husqvarna 257.

 

[Chevboy0167]

Start spraying 1 part at a time till she fires if you suspect over heating connections or module.... I used this trick last week at work to show the "new" younger maintenance guy how the ignition module was cutting out on 1 of our Cat forklifts when it sat and heat soaked, causing a no start.

https://www.ebay.com/itm/121563819119?epid=4012051423&hash=item1c4dc4ac6f:g:yFQAAOSwnHZYeV3Y

 

[Jasonrkba]

Definitely true but 10 year old fuel line, impulse, plug and carb kit. Id do those first as they are due at this point. I had a coil go out in my 025. It would start good make a few cuts and still run but when I hit the trigger after the few cuts it was like I had the brake on. Swapped coil and plug no more issues.

 

[cookies]

sounds like the plug's internal resister is becoming a open once heated up, swap the plug and make a cut. If it still cuts off once warm check for spark or shoot a little fuel in to see if its fuel related.

 

[NuclearNick]

Get that carbon out of the exhaust port before it scores that minty piston. Your probably having carb issues. Get a good rebuild kit and replace the plug. Also if the fuel and impulse lines are original they are ready.

Any suggestions on the best way to clear the carbon out of the exhaust port? I don't want to do it stupidly and create a bunch of carbon flakes that end up in the cylinder.

 

[NuclearNick]

That's a lot of carbon. What oil are you using?

Have you changed the fuel filter ever? Might be worth doing so.

No need to rebuild the carb unless you know it's the problem. Saw carbs have some small delicate parts in them.

The OEM carb is a known quality piece. AM carbs can be anywhere from ok to junk. Same with carb parts.

Have been running with the Sthil "high performance" oil (orange bottle). Sound right?

 

[stihltech]

fuel line #1

 

[Stihl Learning]

Any suggestions on the best way to clear the carbon out of the exhaust port? I don't want to do it stupidly and create a bunch of carbon flakes that end up in the cylinder.

Put a cap of Seafoam in a full tank of gas and run it. It should clean up after a few tanks. I would spend the extra money and run the Stihl HP Ultra (Silver bottle) oil.

 

[Jasonrkba]

There is a process for it. With the muffler off and the piston up use a wooden dowel or pop cycle stick to carefully scrape it. Don't scratch the piston. I always flush with WD-40.

 

[ericm979]

Have been running with the Sthil "high performance" oil (orange bottle). Sound right?

I have not used it myself but it has a reputation for lots of carbon deposits. I think the orange bottle stuff is not synthetic.

I use a high quality low ash synthetic and I don't see anywhere near that much carbon.

 

[sonny580]

Had the fuel line go out on the first 250 that a guy threw in the trash can and I felt sorry for the saw and brought it home! They dont last long. anyway after the fuel line it ran but not right and carb had tops on it so you couldnt set it and I broke the needles off getting the plastic off so I put a $9.95 chimina knock off on it that had screws that you could set with common screwdriver and after some fine tuning it ran great. also a new plug helps!
The second 250 I actually bought,----ya, sonny BOUGHT a sthil! lol!, anyway it ran great for 1 day then dead! nuttin! coil died in it so back to ebay and a chinima knockoff coil for it and it even came with anew plug and saw runs like new again. The 025 had a few nasties in it but after some serious setting and new coil for it , now it too runs and none of the 3 are too hard to start.

 

[woodpecker59]

Hello all,

I've been using an MS 250 for about 10 years for limbing, etc and it's been very reliable. Went out to use it today (haven't run it in about 2 months) and it starts just fine but dies off after I run it for a few minutes, usually when I get done with a cut and let off the throttle. Hard to start after it dies - have to put it in full choke and give it a pull, then starts after a few pulls in half choke. Drained gas that was a few months old, put in new gas. Replaced air filter with new air filter, same problem. I haven't attempted any surgery yet. Willing to pull this thing apart, but don't want to do so randomly.

Any sharp Stihl mechanics out there with ideas what might be causing this? It's been a good little saw and I'd like to keep it running a few more years.

Thanks!

Hi Nick,
I had the exact same issue with my 025, would start just fine and then after it warmed up, would die. My fix, ( and I think it was mentioned in another reply) was to replace the coil with anO.E.M. coil.
Now, I can only speak for myself here, but I have owned that 025 for twenty years, so even though the coil was a bit pricey, it was worth it to me. In addition, I was a bit worried about the actual removal and replacement. There is an Excellent YouTube video on how to swap the coil out. Mine has been running just like new since I replaced it. Hope this helps.

 

[TRTermite]

Hi Nick,
I had the exact same issue with my 025, would start just fine and then after it warmed up, would die. My fix, ( and I think it was mentioned in another reply) was to replace the coil with anO.E.M. coil.
Now, I can only speak for myself here, but I have owned that 025 for twenty years, so even though the coil was a bit pricey, it was worth it to me. In addition, I was a bit worried about the actual removal and replacement. There is an Excellent YouTube video on how to swap the coil out. Mine has been running just like new since I replaced it. Hope this helps.

You are welcome to visit the Peanut Gallery (It is a Quiet Place) and Observe how your post plays out..

 

[cookies]

A easy way to remove the carbon is pop the muffler off, soak a rag with diesel, marvels or 2 cycle mixed gas and set the piston to tdc to block the port off. pack the wetted rag in the port and let it sit to soften the carbon. It might take a day or three days and require rewetting the rag, once softened it will become gummy and should wipe out using the dampened rag, no need to scrape. As stated use wd-40 or I spray fuel mix with a squeeze bottle to wash it out. If its being a real pta cut the rag so it fits in the port, spray the rag with carb cleaner to soak it then tape over it to seal it in and let it sit a hour. Stihl orange is good oil, smokes and leaves carbon but I find it comes off pretty easily, stihl silver bottle can carbon up stuff bad and be harder to remove. I like the vp brand 2 cycle oil in hotter temps and schaffers 9000 in colder temps, everyone as their own favorite flavor of 2 cycle oil. The oil thread is over 1,000 comments and provides a geat many brand options to try.

 

[MRCLYDE]

How about the tank vent, I'd trythe simple stuff first.

 

[J D]

Hard to start after it dies - have to put it in full choke and give it a pull, then starts after a few pulls in half choke.

That's a pretty good indication the fuel supply is restricted... I'd start by flushing the tank & seeing what comes out, then replace filter & pressure test carb through the fuel line at the same time if you can.
If the carb & line hold pressure & the filter doesn't fix the problem then it's time to strip the carb down

 

[sand sock]

change the fuel line
clean the exhaust port.
pull the spark arrestor and soak that muffler in gas to clean it.


hopefully that is it. . could be a carb, but maybe your crank seal is leaking, after things warm up. it sucks more and fails after its warm. my old 034 spun in the case as the bearing froze.

 

[TRTermite]

So is the OPs' Ms 250 up and running? If so what was the successful fix?

 

[NuclearNick]

So is the OPs' Ms 250 up and running? If so what was the successful fix?

I got slowed down by my darned day job :-(

Based on all the good advice, and after watching about a hundred you tube videos, I decided to totally tear this thing down, clean it up and replace all the soft parts (fuel line & filter, oil line & filter, carb rebuild, etc). Also putting in new plug and ignition coil (finally going with OEM coil because the first 2 chineseum coils I received were slightly different dimensions and wouldn't fit). Fixing some oil leaks, replacing oil drain plug. I should have it back up an running this weekend, fingers crossed. I'm probably changing too many things at once and might never know which was the real culprit - I suspect the coil. But as long as it works and lasts another 10 years then it will be money well spent.

In the meantime I pulled out my other 3 chainsaws and am starting to bring those back to life - dad's old 028AV wood boss, a cheapo homelite 35 cc that I left fuel in 2 years ago (oops, replacing all the fuel system parts now) and almost new Poulon pro that was gifted to me but I've never used. Hopefully I can get something up and running soon - many trees down here that need cleaning up.

 

[Fatherwheels]

I use an old credit card, or wooden skewer to scrape back the carbon,
first I use a cotton bud to soak the carbon with bleach, nice and gently
not splashing it on the cylinder, after soaking I begin with an old tooth
brush to pull the carbon back away from the cylinder, put more bleach
on the toothbrush and massage in carefully, this works good for me, I
use the wooden skewer to pull the carbon closest to the cylinder away,
or an old credit card if the carbon is tougher, cut it to shape.

I steep the the spark screen in 1/2 inch of bleach in the bottom of a suitable
glass, after a few hours, I use the toothbrush to remove the dissolved soot, and
steep again if required and repeat, always works well for me, but I clean the screen
on a regular basis so its never really a lot of work and only a few hours steeping
required, I have never had to use a gas torch to clean a spark screen.

Run a different oil to cut down on that carbon, but having said that, your piston
looks like it was well protected by what ever oil you used.