Stihl ms 250 problem

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sonny580

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Any ideas of why a 250 kicks when you pull the starter rope???--- If it sets a couple months, it won't even try to start.--just tries to jerk the rope out of your hands.--hard on fingers! lol!! Prime carb, it rolls over likes it is starting then dies.--won't even fire after that.
Saw has been a problem to former owner who gave it to me because he couldn't do anything with it.--He bought it new and could only use it if I went over and started it for him.--Got him to take it back to the dealer and they wouldn't try to fix the problem!
Last year he tossed it into my truck and said IF you can get it to run, it's yours.--after replacing the fuel lines I did get it running, NOT real good but it sure would cut! ran it hard and got tired out and shut it off.--half hour later I wanted to cut some more brush and it would not attempt to fire, just try to tear your fingers off.--wanted to set carb, but they had it blocked and I gave up on it and got the homelite sxlao out and finished the job.
My wife found a "will fit" carb from china, ( original was stihl,zama,china) on it so figured why not try.--put new carb onand set it with plain ole screwdriver and primed carb, FINALLY got it to start, set needles and cut a bit.--shut it off went back half hour later and second pull, it wanted more wood!
Good saw, but this starting thing is kinda rough on and old man!! LOL!!!! --any ideas??? thanks; sonny580
 
Take the flywheel off and see if the key is sheared. Kickback when started usually means the timing has changed and the flywheel is able to rotate on the crank.


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This. Make sure the pickup is tight and properly set.

Also replace that carb with a Walbro 194. Allows H and L adjustment, drill a couple 3/8 holes in the muffler and standby for a totally new saw. Don’t forget to readjust your carb for the muff mod.

If timing is fine (no sheared keyway) check the sparkplug wire, it may be loose/corroded/worn and shorting out.
 
@sonny580,

Is the issue how hard and jerky it is to try and pull the rope on it? Mines the same way.....dealer assures me I'm a wimp. When cold I usually have to set it on the ground and plant a foot in the handle to be able to pull it through. Starts and runs ok and usually much easier to re-start once I've warmed it up.

I'd use the saw more if it wasn't so cantankerous. Wish I knew how to fix it.
 
Take the flywheel off and see if the key is sheared. Kickback when started usually means the timing has changed and the flywheel is able to rotate on the crank.

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Amen to that. I had the same thing happen to me with a 290. Sheared key, loose flywheel nut. That thing needs a gorilla to tighten it. Not having King Kong around, I added a 12" pipe extension onto the socket wrench handle when I fixed it. The key does practically nothing to hold the flywheel tight. It's just a position holder.
 
My 250 is super hard to pull. It's not kicking back or hard to start, it's hard to pull the cord. Runs fine once it's running. Everything turns fine when the plug is removed- starter, crank, etc. It's acting like it has too much compression. I bought the saw new 20 years ago and it's never been apart. It was used a few times a year for many of those years but I've been using it a lot for the last year and a half. It's gotten harder and harder to pull lately, so much that I'm worried that I'll break the cord.
 
My 250 is super hard to pull. It's not kicking back or hard to start, it's hard to pull the cord. Runs fine once it's running. Everything turns fine when the plug is removed- starter, crank, etc. It's acting like it has too much compression. I bought the saw new 20 years ago and it's never been apart. It was used a few times a year for many of those years but I've been using it a lot for the last year and a half. It's gotten harder and harder to pull lately, so much that I'm worried that I'll break the cord.
Try taking out the spark plug and see if it's still hard to pull. If it is, you have a lock up or blockage somewhere that's unrelated to compression. It could be the chain brake is not entirely disengaging, but if that were the case I would be surprised if it started and ran at all.
 
My 250 is super hard to pull. It's not kicking back or hard to start, it's hard to pull the cord. Runs fine once it's running. Everything turns fine when the plug is removed- starter, crank, etc. It's acting like it has too much compression. I bought the saw new 20 years ago and it's never been apart. It was used a few times a year for many of those years but I've been using it a lot for the last year and a half. It's gotten harder and harder to pull lately, so much that I'm worried that I'll break the cord.
Take off the muffler and snap a pic of the piston, take the pic with the top of the piston in the pic.
 
My 250 is super hard to pull. It's not kicking back or hard to start, it's hard to pull the cord. Runs fine once it's running. Everything turns fine when the plug is removed- starter, crank, etc. It's acting like it has too much compression. I bought the saw new 20 years ago and it's never been apart. It was used a few times a year for many of those years but I've been using it a lot for the last year and a half. It's gotten harder and harder to pull lately, so much that I'm worried that I'll break the cord.

Sounds just llike mine....except mines two years old.
 
It's hard and jerky on cold start!!--After it's hot rolls right over pretty good!---Guess I'm a wimp too!! LOL!!!
I checked all the parts and they seam to be in order.--This 250 is between 15 to 20 years old and probably has about 100 or less hours runtime on it!--I've had it for several years and last winter I decided to fix it or drop it under MOOSE track!! LOL!!!--(just kiddin about MOOSE trackin it!!) lol!!--I have an aftermarket ignition module and was going to try that, but hate to go to all that and still have the same problem!!---Just my personal thought,---- it feels like the spark is too early on the compression stroke,--fires before piston gets all the way up, making it kick/jerk.---I too am afraid that I will break the starter, or it will break my fingers!!! ( not real good grip anymore, arthrites real bad)---Last year I put the de-barker on it and made a deadly monster out of it!! Talk about the bark flying!!--It just plays with the head but sure works your butt off!! thanks; sonny580
 
Try taking out the spark plug and see if it's still hard to pull. If it is, you have a lock up or blockage somewhere that's unrelated to compression. It could be the chain brake is not entirely disengaging, but if that were the case I would be surprised if it started and ran at all.

I did that and said so in the post that you replied to.
 
The way the exhaust port turns down you can't see the piston crown at BDC through it. But here's a pic with a cheap borescope down the plug hole. Looking at it with my eyes there's a little more carbon in an area about the size of a nickel concentrated on the intake side under the plug. You can just see the start of it at the bottom of the pic. I scraped some off and it's not that thick. I've seen this much or more on two stroke motorcycle engines that were running well. The exhaust skirt of the piston looks super clean. I can still see the faint grooves they machine on it. Often those are worn down.



2018-02-07-084703.jpg
 
The ring grooves won't have any. If they did, it wouldn't matter..

The top of the cylinder may have some, but see if taking crud off the top of the piston helps.
 
Stihl made a decarbonizing solution for 4 mix engines, which contained EDTA, a chelating agent. My dealer tells me it is NLA. You poured it into the cylinder and let it soak, then poured it out. Supposedly it worked. It was even rumored to remove aluminum transfer (although its anti-cancer properties were unable to be substantiated). I have looked for it for a while and have never found a seller who still had it in stock. Anyone know of any?
 
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