Stihl ms250 problems again

[flybyjohn]

I had a problem with the accelerator pump on my ms250 quite a few years back. I plugged the hole and it ran flawlessly since then until just the other day. I am using the saw up in my hunting area to cut all the blow down trees out of my hunting spots. The deadfall has made it impassible for both 2 legged and 4 legged critters. Anyway, I am leaving the saw up there for the week chained to a tree and covered with a plastic bag under some pine branches. That way I don't have to pack it in and out every day.

The problem, when the saw is cold, it will fire up after three pulls on full choke and two pulls in run position. It seems to run just fine for the first tank of fuel. I run out and then go refuel it and when I get back to starting it again, it will start with full choke one pull followed by 3-4 pulls off choke, (when hot after refuel it won't start without going to full choke for at least one pull, it used to start with one pull without choke when hot). It will idle fine but when you go to full throttle, it bogs and dies. Sometimes if you get it under a load before it dies, it seems to help it pick up and go to full throttle. After messing with it trying to feather it to full throttle, and if you get it there, it will start to run just fine and run the whole tank through without any problems until you refuel again. If you shut it off, it will still start just fine as long as you don't let it sit for more than a couple minutes, after a couple minutes your right back to the bogging problem again.

Anything obvious I should be looking for. Does a saw need a retune from 30 degree weather to 90 degree weather? Like I say, once it gets up to full throttle after restarting, it runs fine from then on until you refuel again. And sometimes it seems like getting the saw under a load will help it get up to full throttle when it is bogging.

 

[Kenskip1]

First question is how old is the mix? You stated that the saw has an accelerator pump. Sorry to disappoint you but it does not. From your description it sounds like it could be vapor locking. This may cause the saws engine to run excessively lean When you run it out of mix this can cues the engine temperature to raise and literally boiling the mix or vapor locking. Solution? Do not let it run out of mix. And yes the saw should be retuned going form 30 degrees to 90. As you mentioned letting the saw sit for a few minutes and restarting, it sounds like it is running to lean. Sitting after running is allowing the heat to saturate the engine. Remove the recoil and make sure the fins are free from dust, chips ext.

 

[Wood Doctor]

Agree with Kenskip1. Sounds like it's running too lean and/or starved for fuel. That's why it pops on choke even when warm. Open the Lo speed setscrew a half turn and see if it co-operates better. You may have to do the same with the Hi. Just yesterday I fixed another saw this way that was performing the same as your MS250.

 

[ericm979]

It's running poorly after you use the choke on a hot start because there's too much fuel in the engine. You're not supposed to use the choke for a hot start, only cold. Once you get the engine running enough to use up the excess fuel, it runs ok.

You're having to use the choke for the hot start because the carb is not adjusted correctly. You should follow Stihls directions in the shop manual. Shop manuals are available in the "beg for manuals" thread. Basically you return to the factory default setting and tune from there. It helps to have a tach but you can do it without the tach. The high end of the idle rpm range given in the procedure is about where the chain clutch starts to engage, and it won't run well much below the low end of the range no matter what settings you use. So as long as it's between constant stalling and starting to grab the chain, its about in the correct idle range.

If I had to guess I'd guess that the low speed mixture is too lean but its best to follow the procedure rather than randomly twiddling screws.

It's possible that the carb has something wrong inside but since it runs ok once started that's unlikely. In any case it's best to start with a proper adjustment and see if that works.

 

[flybyjohn]

Thanks for all the help so far. The fuel was mixed last Thursday with ethanol free gas and Stihl ultra synthetic oil 50:1. I thought it was a Zama carb. I think the numbers on the side were "s76c" . It's been a long time but I think I made a plug for item number 35 a few years back out of aluminum on the lathe and pressed it into place and used some sealant to make sure it stayed sealed.

 

[Kenskip1]

Quote "It's running poorly after you use the choke on a hot start because there's too much fuel in the engine. You're not supposed to use the choke for a hot start, only cold. Once you get the engine running enough to use up the excess fuel, it runs ok."

How about he is using the choke to help draw fresh cool mix into the engine. Once the engine has the cool mix it runs normally. As to the users manual they will have the saw running very lean. This is what is causing me to be suspicious in the first place. Chances are it may need a rebuild kit.

 

[flybyjohn]

I did tune it with a tack but it was quite a bit cooler then. I didn’t think much about tuning for the higher temps because everything I read online only had the flipping of the baffle to change from summer to winter running.

Kenship1, was i wrong to call that part of the carb an accelerator pump. What ever its called, I saw the hack for it done for the 200t because it was problematic back about 5 years ago so I made a plug for it and pressed it in place and retuned it with the tach. It has run great up until cutting this summer with it. All my cutting before has been fall and winter.

 

[lone wolf]

Always like this or is it doing it in the high heat? Can it be vapor locking ,will it always start and run good after cooling?

 

[flybyjohn]

When cold or first start of the day, it takes 2- 3 pulls on full choke, it pops, I take off choke and fires up 1-2 pulls after that and runs just fine, no loss of power that I can notice. I can turn it off move some branches and restart it No problems. If after I run it a while and shut it off and wait 15 minutes, it has a hard time starting without choke on but the saw is still pretty warm. I will admit that I do try to get that last cut done before it finally runs out of gas. I will stop doing that. In the cool / cold weather, I have never noticed this condition.

I did have a problem with it bogging 5 years ago and made a pressed fit plug of aluminum to fit into where 35 goes after removing 36, 37, and 38 in the picture above. It solved he bogging imediatly and retuned it. It have run great until the other day in the heat.

 

[lone wolf]

When cold or first start of the day, it takes 2- 3 pulls on full choke, it pops, I take off choke and fires up 1-2 pulls after that and runs just fine, no loss of power that I can notice. I can turn it off move some branches and restart it No problems. If after I run it a while and shut it off and wait 15 minutes, it has a hard time starting without choke on but the saw is still pretty warm. I will admit that I do try to get that last cut done before it finally runs out of gas. I will stop doing that. In the cool / cold weather, I have never noticed this condition.

I did have a problem with it bogging 5 years ago and made a pressed fit plug of aluminum to fit into where 35 goes after removing 36, 37, and 38 in the picture above. It solved he bogging imediatly and retuned it. It have run great until the other day in the heat.

Could be the gas . Try Av gas in the heat and see if it does the same thing.

 

[Kenskip1]

Always like this or is it doing it in the high heat? Can it be vapor locking ,will it always start and run good after cooling?

Read post two.

 

[lone wolf]

Read post two.

I park my saws in the shade and the gas can too when possible on the hot days that seems to help with the vapor lock. You dont know how old the gas is they are selling.

 

[flybyjohn]

I will be headed back up there tomorrow. Will make sure all fins are clear and richen it up a little bit. I’ll check to see just how far from the factory tune I’m at before I start. I might pull the muffler real quick too and have a look at the piston. My bigger saw would probably cut faster but having to throw that saw around in every direction and angle would just about kill me.

This is what I’m clearing out. That beetle killed wood is falling down just as fast as it died now. I sure wish it wasn’t a mile from the road, I’d be taking it home for firewood.

 

[Captain Bruce]

I had a problem with the accelerator pump on my ms250 quite a few years back. I plugged the hole and it ran flawlessly since then until just the other day. I am using the saw up in my hunting area to cut all the blow down trees out of my hunting spots. The deadfall has made it impassible for both 2 legged and 4 legged critters. Anyway, I am leaving the saw up there for the week chained to a tree and covered with a plastic bag under some pine branches. That way I don't have to pack it in and out every day.

The problem, when the saw is cold, it will fire up after three pulls on full choke and two pulls in run position. It seems to run just fine for the first tank of fuel. I run out and then go refuel it and when I get back to starting it again, it will start with full choke one pull followed by 3-4 pulls off choke, (when hot after refuel it won't start without going to full choke for at least one pull, it used to start with one pull without choke when hot). It will idle fine but when you go to full throttle, it bogs and dies. Sometimes if you get it under a load before it dies, it seems to help it pick up and go to full throttle. After messing with it trying to feather it to full throttle, and if you get it there, it will start to run just fine and run the whole tank through without any problems until you refuel again. If you shut it off, it will still start just fine as long as you don't let it sit for more than a couple minutes, after a couple minutes your right back to the bogging problem again.

Anything obvious I should be looking for. Does a saw need a retune from 30 degree weather to 90 degree weather? Like I say, once it gets up to full throttle after restarting, it runs fine from then on until you refuel again. And sometimes it seems like getting the saw under a load will help it get up to full throttle when it is bogging.

You have water in both the fuel tank, carb, and in your gas can....

 

[cscltd]

It could also be that your plug and/or sealer is leaking from the accelerator pump valve that you blocked years ago as that would cause it to run erratic

 

[flybyjohn]

Water in the gas and tank are pretty low on my list. I take in the gas and oil everyday and back out again at the end of my session. I have run the tank dry quite a few times before I found out I wasn’t supposed to do that. I fill the gas and oil full everyday before leaving. I have the gas in a clear plastic 2 liter bottle for easy transport In my backpack. If there was water in there I should see it. It hasn’t rained in over a week and the saw is wrapped in a plastic bag to keep the odor from any curious critters. Bears like to mess with just about everything I leave there. Hopefully they won’t find the saw.

 

[flybyjohn]

Could be my plug leaking slightly at different temperatures.

 

[Alder]

Just out of curiosity approximately how far would you have to pack the saw if you packed it in and out every day?

 

[Brushwacker]

To me it sounds you could be getting to much fuel which could be less of a problem when the engine is cool or not so hot.
Is your air filter clean and porus. Sometimes they look clean but can be plugged with fines or dry fuel . May remove it when your having problems and see if acceleration clears up or just try a new 1.
Also check your spark plug color. That might give away an lean or rich condition. A new 1 run a while regular use usually is easier to read. Make sure the gap is .020 in. , wider often causes issues.
Do the easy things 1st and go from there if it doesn't correct it. You might fix it at that and likely can fine tune it better adjusting the carb to current conditions.

 

[flybyjohn]

About a mile one way and up a steep hill coming out. I packed it in and out the last few years but after back surgery in February, it’s all I can do to get my bug butt out of that hole after throwing 6-8 foot logs for several hours. I went in and started cutting Friday, Saturday, Sunday , Tuesday, and will be going in again tomorrow and Friday and Saturday. Then I’ll bring the saw back out.