MS250 Tune-up for dummies.

[Old Greenhorn]

Hey all. My son-in-law has used a chainsaw all his life, but working on them is not his strong suit and in many ways, it isn't mine either, but I try.
 I got a call yesterday that his saw quit, can't keep it running, thought he burned up the clutch as the chai would stop sometimes, now it won't start, he did the air and fuel filters, no help. He tried tuning it, still no joy. He was looking for someone to take it to, but I had nobody to recommend, so I said bring it by and let me have a look.
 So my daughter dropped it off an hour ago. First thing I noticed was the chain was a tight as a high G-string (on a banjo) and there was a blue streak around the outside edge of the bar. >:(

 There was no way I could pull that chain around by hand. I removed the B&C and the clutch drum. Cleaned that out, clutch looks good but had some ugly build-up. Put it back on with some grease on the bearing and checked where the carb settings were then screwed them all the way in and came out half a turn with each to start.  It started right up, but idle was very high. Oil pump worked fine. SO I shut it down and dressed the huge burr off the sides of the bar then put it all back together.
 Started right up, but still high idle and chain would not stop. (I had not yet found the hidden low idle adjust screw.) So I ran a couple of cuts on a log, power was good, chain sharp, it cut well.

 So I tried messing with the carb settings more, but I am hunting like a blind man. I don't know Stihls at all, never owned one. Barely competent on my Husky's. Can anyone give me the start points? You know what I mean? Go fully closed then back off "x" turns, that sort of thing. Usually that gets me in the ballpark. But these screws are tough to access and get a tool onto and really tough when the saw is running. Just need a start point, I think.  It took me a while to figure out that the low idle screw was hidden behind what I will call a 'secret sneaky hole' in the handle side and I can't seem to get a screwdriver to catch in the screw slot to adjust it. Very frustrating. Wish I knew a local guy that was good at this stuff, but I think maybe I am smart enough to follow instructions from one of you smart fellas. Any suggestions and support would be appreciated. Is there a special tuning tool for these saws or something? Is there a counseling group for Husky guys trying to work on Stihl's? :D ;D

[Old Greenhorn]

Actually, I have been looking at you tube videos and am now wondering if I am even using the right screw driver. Is it Philips or straight and what diameter? Are all 3 adjustments the same tool? I have been using a pretty skinny straight driver and maybe that's part of my problem?

[lxskllr]

The "official" tool I got with a normal carb Stihl was a little flathead screwdriver. That got stolen a couple years ago, and I don't remember the particulars. My current Stihls are computerized. I do remember the screws were so far in the case they had a different zip code. Try shining a light in the hole to get a better idea of what the target is.

[Old Greenhorn]

First thing I did was grab a flashlight and that helped with two screws, but that low idle screw it was useless because, as you say, it's WAY in there and I can't even feel for anything. But in one video I saw a guy using what I thought was a fairly good sized flat(?) screwdriver, (maybe 1/4" diameter or more?) which made me wonder if I was using a tool way too small allowing me to go right past the screw if I was just a bit off on guessing (or divining might be more accurate) the angle.
 Let's just say there is not a lot of joy at my workbench right now and the air is turning blue. ;D

[twar]

There are variations of the 025/250, but most of the ones I have worked on are like this one (a 250): 


 

So both H&L all the way in, then back out 1 full turn. Once it's running, I play with the L to find the highest idol. You hear the RPMs fall if you turn in past a certain point, as well as when you turn out past a certain point. Once I've found the L setting, I play with the idle.

I use a thin 1/8" flathead to adjust the carb (also a flathead on the idle screen, but it's a coarser screew). What makes finding/hitting the screen is the boot between the screws and the outside of the cover: 


 

You can remove it to make the adjustments, and I have opened saws that lacked the boot (perhaps it didn't get put back).
I hope this helps, but like I said, there are variations. But again, all the 025/250s have been 1 full turn out (as a starting point at least).

[doc henderson]

OK, I got a few pics too.  250c ez start was my sons first chainsaw.  now 24 and he got it at age 12 or so.  



 

looks like the turnout is different for the high and low screw.  I shop at Fairview sales that is an Amish shop.  They are funny but each saw comes with a screwdriver in the box.  The shop does not want their customers messing with the carb, so they pull all the screwdrivers out of the boxes.  I took it as a high compliment, when I was shown the drawer at the shop and told I could have all I wanted.  



 

 


   :D :D :D    8) 8) 8)    

[Old Greenhorn]

Twar, Doc, thanks for that info, it all helps. The saw he has looks just like Doc's rather than Twar's example (Talking about the starting screw turns). I will just have to search harder for the screw heads I guess and look for a slightly larger screwdriver.
 I am also wondering if I can get this working properly without taking off the limiter caps, which I am assuming it has.
 Doc, I wish somebody had taken my SIL's screwdriver away, my job would be easier. :D ;D

[twar]

Yes, this confirms/supports my experience; there are different versions of the 250. I have seen them with and without the limiter caps. 

Another thing I didn't think about is that the ones I've worked on have all been European versions sold here in Norway or Sweden. Emissions standards (and therefore model configurations) have not been the same here as over there.

[Old Greenhorn]

Yes, that's true, for instance, this version does not have a primer bulb like the two examples shown, I think that might make it older?
 I am not a stihl guy and this is only the second one I have tinkered with. On my best day, with Husky's I still suck at tuning and don't have a tach. So, it becomes a very short trip for me to go a little crazy when something like getting at the screws presents such a difficulty. I know this is fundamental and if you can't get that right, you needn't try to move past that. This morning I began again, clean, clear, and calm. ;D
 I first looked for a better screw driver, then remove the air filter base so I could visualize the actual screws and get the right feel for hitting them predictably. I then began with fresh setting from scratch. It took a while of balancing between settings, test cutting, warming up, and trying again. After 1/2 hour of messing and balancing I finally got the high rpm's about where it should be and the low idle to sl9ow enough for the chain to stop. (This last had been a problem, low idle seemed unreliable and too fast.)
 My method was more of the blind squirrel and the nut, just hunting around and trying everywhere when at one point I just hit it on the head. It idles down but does not stall and the chain stops, come up fine with no surge or stall and cuts well. I do have to do a hot start on half choke though, not sure if that is normal for this saw, it does have a LOT of time on it. I think he may be the second owner. 
 The root cause was that chain being too tight and he didn't realize it and the saw kept dying, he tried to adjust the carb and it all went downhill from there.
 Runs good now.
 Thank you ALL for your help and getting my head in the game. I knew I could figure it out but I had to get the basics square in my head first.
 Apparently even a dummy can do this with a little patience and support from friends. ;D :D

[JD Guy]

OGH, Good for you to keep after it! What the others said above is correct. The rubber "boot" should, one would think, make it easier to find those carb screws but in fact is a PITA until you figure out the relationship between the channels in the boot and the screws. Mine is very easy to flood if given one too many pulls at full choke when cold. The only saw I have that's that persnickety. You're a good man to help out your SIL 8)

[Old Greenhorn]

Well to be fair, I felt a bit of urgency for them. They closed closed on the house they are living in back in March or so after living there ten years. They are in that wonderful stage of ownership where they can finally make it the way they want and fix a lot of the 'innovative' 'features' that the original owner/builder put in.

 See if this sounds familiar: They can't finish the kitchen tear-out to begin the rebuild until they get some of the bigger tools and such out of the way, so they need to build a storage shed. They can't build the shed until they can cut up and stack the log pile that is in the way first, and they can't cut the wood if the saw is broke down. Ever happen to you? Well, it's happened to me in one form or another. SO the whole thing is 'my fault' if it doesn't get done. :D :D
 Gotts keep the kids working so they can take care of me when I get old. ;D I may be living in that shed. :D (I hope it's a nice one, with a window.)