Stihl MS250 mixture screws?

[dodge man]

I have a Stihl MS250 that is about 15 years old. I would call it occasional usage but over the years it has accumulated some hours. Newer spark plug and air filter.

Problem has been going on for a couple years. It will idle badly but keep running if you goose the throttle a little. It will also bog down and die unless you work the throttle slowly when going to full throttle in wood, but once pulling hard it runs fine. Last time I used it I played with the two screws a little to make it idle better and transition to full throttle better. It ran perfect. Problem is the will most likely repeat where it will run bad.

I do not think it is fuel. I have several Stihl tools and all run the same fuel and they run fine.

 

[pmsmechanic]

I've had reasonable luck just gently turning in the screws till they seat and then turn them out again to where they were. What this does is clean junk out of the seat. It also helps to gently turn the screws in till they seat counting the turns on the way in. Then remove the screws and flush the hole out with a bit of brake clean.

If that doesn't work then you will eventually need to take the carburetor apart and clean it.

 

[pmsmechanic]

Double post grrrr!

 

[dodge man]

Thanks. I wondered if the carb needed cleaned.

 

[ovrszd]

I've got a 9 yr old 250 and a 361.

The 250 is very picky in regards to fuel. You have to feather the throttle to get it to rev up. The 361 never acts that way.

May be a simple adjustment but I've always gotten over it with fresh fuel.

I'm curious to see if you find an adjustment solution that might make mine not so picky.

 

[ericm979]

It sounds like it's a bit lean. A little richer on the low speed should help that.

When I end up with carb settings that keep going off, I return the settings to the default (usually 1 turn on Stihls but check the manual) and tune from there. Sometimes you can get a setting that seems good but is way off the factory setting and won't be good the next time you run the saw. Starting over often fixes it.

 

[ruffdog]

If simple adjustments/repairs don't get it running right, you may have a air leak. That may be a bad crank seal, pulse line, or the clam shell joint leaking air.

 

[dodge man]

I have backed the mixture screws in and out to the factory settings. The turns is printed on the side of the saw. It could be sensitive to fuel. This last time it ran good it had newer fuel. I guess just because my other stuff runs fine doesn’t mean the saw is not mo sensitive.

 

[ericm979]

Some of my two stroke equipment is fairly insensitive to fuel age. I have a Husky backpack blower which runs terribly unless the fuel is fresh. It's carb is totally non adjustable, not even tamper resistant adjusters (which I have the tools for). A slightly richer mixture would fix it but there's no way to change it.

 

[pmsmechanic]

Some of my two stroke equipment is fairly insensitive to fuel age. I have a Husky backpack blower which runs terribly unless the fuel is fresh. It's carb is totally non adjustable, not even tamper resistant adjusters (which I have the tools for). A slightly richer mixture would fix it but there's no way to change it.

So look for an older Husky with the same model engine and buy an adjustable carb for the older model. They run about $40 on the internet.

 

[nyone]

Make sure you check the spark arrester. They do clog up.

 

[WranglerX]

My MS 250 got a bit cranky to run.. Tweaked the idle mixture and idle speed screws by the manual and it runs great again... Does not seem to be sensitive to old or new fuel....

Dale

 

[circled]

When my MS250 gets running rough I pull the spark arrestor and burn it clean, then add about an ounce of seafoam to the fuel. After a minute or two at WOT it always seems to return to normal for another year! Maybe dumb luck, but it works for me. Good Luck!

 

[dodge man]

I suspect I need to pull the spark arrestor. I assume this is the thing that looks like a muffler? How do you burn it clean?

 

[RandyT]

I suspect I need to pull the spark arrestor. I assume this is the thing that looks like a muffler? How do you burn it clean?

Propane torch works wonders on those arrestor screens. Just something to get them hot enough to burn off the deposits.

 

[Rebeldad1]

My MS250 had problems and I just replaced the carb. Seems to me it was under $25.00 for a new one.
Almot ALL my 2 stroke engines quit having problems when I switched to Pure fuel. I add Seafoam, PI fuel conditioner and Octane booster to my 5 gallon can. I use this on all the small engines. Mower, generators etc. I also spray the carbs once in a while with PowerFoam as a maintainence cleaner. I use a marine (Amsoil) 2 stroke 100 to one mix with this for the saws.

 

[nyone]

What octain where you using? Most stihl saws require 91*. I have been using 93* e0 fuel in all my small equipment as well as fuel stabilizer.

My problem with the spark arrester getting clogged happened to be from me useing to much oil in my mixed fuel. Check your saws spec, if your mixing correct maybe it's time to change oils.

 

[ericm979]

So look for an older Husky with the same model engine and buy an adjustable carb for the older model. They run about $40 on the internet.

I'm embarassed to say that I didn't think of that. I bought a $10 ebay carb with adjustments and went to put it on today. Unfortunately I'd forgotten that the blower I have is a "CARB II" model from the early 2000s and has a funky two bore carb. The small secondary bore goes to a tiny reed valve in the intake manifold and then there's a hose to the crankcase. It looks like some sort of stratified charge thing. The regular type carb does not bolt on to the manifold. I might be able to find the non strato manifold parts to adapt it but since the parts are from the 2000s and many are no longer available it might be tough. Bummer, it was a good idea.

 

[dodge man]

I’m running 91 octane and Amsoil 2 stroke oil at 50 to 1.

 

[dodge man]

I took the spark arrestor apart and I don’t think that was the problem. It is generally running good but still will not quite idle but it does throttle up. I suspect it is just sensitive to needing fresh gas. When I had the spark arrestor off I could see score marks on the piston through the exhaust port. I am not sure if that is normal or not.