Stihl ms250 bogging at full throttle

[oakchop]

I've seen what you describe inside chainsaw carbs that is so fine it gets past the in tank gas filter and clogs/restricts the screen in the carb. Saw usually idles and runs fine piss reving out of the cut but start bogging in the cut under load.

Most generally what I find is a very fine of what appears to be a mold of some sort attached to the walls of the fuel tank and very hard to remove. Almost like baking soda consistency and also I've seen different colors of the mold. Can be seen on fingers when a finger is wiped in the gas tank wall and sometimes can be seen with a good flashlight inspection.
I suspect it forms if a gas tank is left completely empty for long time and even worse if the gas tank is magnesium, galvanized, aluminum types and some plastics types..

Yep it was a creamy white baking soda like paste caked on the screen. I took chunks out with a toothpick and ran it through my fingers and it felt like toothpaste almost.

 

[oakchop]

Yep it was a creamy white baking soda like paste caked on the screen. I took chunks out with a toothpick and ran it through my fingers and it felt like toothpaste almost.

Also the chainsaw did sit without gas stored for a long time before I used it. it was brand new but mold had time to develop in the tank. I'm going to have to try to scrub the tank with a toothbrush or something. pour the gas out, repeat. I was thinking of spraying it out with carb cleaner.

 

[Okie]

I put a bunch of nuts and small bolts inside the gas tanks and just used mixed gas and tied /strapped the really bad ones to my tractor tire with padding so as the saw was really secured good and slow tumbled the whole saw so as the tank would get a good cleaning. (I removed the bar and chain. Jacked up one tractor tire. I could go do other things and check back later, just remove the gas cap/ flush and go again with the saw still in place. I did this to couple of saws that the fine screen in the carb kept clogging quite often. (as often as two tanks of gas or less) The fuel pickup filter and hose is going to take a beating if it's weak.
At least now you know what is happening. It will happen again if the tank is not cleaned good.
You will also find that them chainsaw carb screens can appear clean at a casual glance but if looked at with magnifying glass or removed they can be severely restricted.

 

[oakchop]

I put a bunch of nuts and small bolts inside the gas tanks and just used mixed gas and tied /strapped the really bad ones to my tractor tire with padding so as the saw was really secured good and slow tumbled the whole saw so as the tank would get a good cleaning. (I removed the bar and chain. Jacked up one tractor tire. I could go do other things and check back later, just remove the gas cap/ flush and go again with the saw still in place. I did this to couple of saws that the fine screen in the carb kept clogging quite often. (as often as two tanks of gas or less) The fuel pickup filter and hose is going to take a beating if it's weak.
At least now you know what is happening. It will happen again if the tank is not cleaned good.
You will also find that them chainsaw carb screens can appear clean at a casual glance but if looked at with magnifying glass or removed they can be severely restricted.

Yes Im very glad I came here. This is SaltyTimber's thread and I hope they got their issue fixed. I learned more in 2 days than I knew for years AND my MS250 is running again better than it began.
I think what happened is my saw was new but it was a display model that they ran a few times and then poured the gas out. This saw was in Oklahoma and was shipped to me in Springtown Texas. Mold and mildew is a huge issue here in Texas. The saw was brand new. No signs of usage. not a hint of a scratch or anything. however I think mildew or something has gotten inside this thing.
I did check my piston and cylinder walls and they looked brand new so luckily no damage was done, thus far.
Ill see about getting this tank cleaned out and consider your method. that sounds a bit like the poor man's ultrasonic cleaner! but it just might work. I can't see a toothbrush able to get around too much in the tank.

 

[oakchop]

I put a bunch of nuts and small bolts inside the gas tanks and just used mixed gas and tied /strapped the really bad ones to my tractor tire with padding so as the saw was really secured good and slow tumbled the whole saw so as the tank would get a good cleaning. (I removed the bar and chain. Jacked up one tractor tire. I could go do other things and check back later, just remove the gas cap/ flush and go again with the saw still in place. I did this to couple of saws that the fine screen in the carb kept clogging quite often. (as often as two tanks of gas or less) The fuel pickup filter and hose is going to take a beating if it's weak.
At least now you know what is happening. It will happen again if the tank is not cleaned good.
You will also find that them chainsaw carb screens can appear clean at a casual glance but if looked at with magnifying glass or removed they can be severely restricted.

I think I'm going to take a bunch of small bolts and place them in this fish net type deal I have and shake it on every side with a little throw away gas inside.

 

[SteveSr]

Also the chainsaw did sit without gas stored for a long time before I used it. it was brand new but mold had time to develop in the tank. I'm going to have to try to scrub the tank with a toothbrush or something. pour the gas out, repeat. I was thinking of spraying it out with carb cleaner.

Bigger question is how all that crap got past the fuel pickup filter... or was it talc/soapstone in the fuel line leftover from when the line was made?

I suspect that you won't have any more issues unless you physically see more crud in the tank.

 

[SteveSr]

However Im going to buy me a MS261 (with decompression valve) or a farmboss 271. both are 50cc. im leaning towards the 261.

Trust me, you do NOT want the 271. It is another consumer saw and the 250 is better. The 261 is a PRO saw. Get it with a 16" (preferred) -18" bar.

 

[oakchop]

Trust me, you do NOT want the 271. It is another consumer saw and the 250 is better. The 261 is a PRO saw. Get it with a 16" (preferred) -18" bar.

yes I'm going with the 261. I got extra chains and bar too but everything's 18". In hindsight I should've got 16" on the 250. but yes I'm leaning towards 261. It's far better and slightly more power (5hp).

 

[oakchop]

Bigger question is how all that crap got past the fuel pickup filter... or was it talc/soapstone in the fuel line leftover from when the line was made?

I suspect that you won't have any more issues unless you physically see more crud in the tank.

Yea SteveSr the amount I found on the screen was consistent with new hoses in theory. It was a perfect paper thick layer of this white paste like substance sitting on the screen. it came off like paper when it was wet with gas. after it dried on a paper towel I touched it and smeared it between fingers and it was like a chalky cream. Very odd. Almost pure white. It didn't appear to get past the screen either because the other convex side was showing metal. gas was slowly traveling around or through it somehow in micro sized areas. being this was coming directly from the gas tank and the saw was new but sat a long time, its either mold or it's gas line residues of that chalky like stuff.
I'll know if it comes back. I plan on using the saw for another dead oak tree after this rain passes and then I'll check the fuel pump screen again. one way or another I'll know if it's mold. hell maybe when it was a display someone put a candy wrapper in the tank which melted and turned to a paste. you never know. the variables are infinite.

 

[Okie]

It gets past the in tank filter and starts building up on the finer screen in the carb.
When it's really bad in the tank you can do the tumbling method then catch the gasoline or lacquer thinner in a container and let it set several days and see the fine stuff. It get past the in tank filter because it mixes with the gas/oil. Some will be in the in tank filter but this filter is larger in surface area and still allows enough gas to pass and go to the carb.
The sintered iron type filters in some carbs will clog faster than the screens.

Seems strange but once you encounter such you will not forget such. Really a hair puller.
Install a new carb or a good re-built carb and it's ok for awhile then same symptoms again sometime later.

 

[oakchop]

It gets past the in tank filter and starts building up on the finer screen in the carb.
When it's really bad in the tank you can do the tumbling method then catch the gasoline or lacquer thinner in a container and let it set several days and see the fine stuff. It get past the in tank filter because it mixes with the gas/oil. Some will be in the in tank filter but this filter is larger in surface area and still allows enough gas to pass and go to the carb.
The sintered iron type filters in some carbs will clog faster than the screens.

Seems strange but once you encounter such you will not forget such. Really a hair puller.
Install a new carb or a good re-built carb and it's ok for awhile then same symptoms again.

yea I'm going to really keep checking on this regularly. I don't want to establish what it is and try to learn from it. I pray it resolves soon. I can't afford any downtime. we're relying on firewood for heat.

 

[Brushwacker]

I prefer leaving my fuel tank most of the way full with fresh non ethonal fuel when parking the saw for more then a few weeks. A little room for expansion and to add a shot of fresh fuel if it sits long. The small amounts of fuel left in the tank and carb tend to dry or spoil more readily then large amounts which retain freshness usually much longer and leave little room for condensation which can cause problems.

 

[SteveSr]

Seems strange but once you encounter such you will not forget such. Really a hair puller.
Install a new carb or a good re-built carb and it's ok for awhile then same symptoms again.

I only ran into this once and that was in an old 025 (predecessor to MS250). The tank had some crud in it so I decided to try to clean it out with lacquer thinner. It turns out that the lacquer thinner / mechanical agitation dissolved an oxidized layer on the inside of the tank. Next time that I ran the saw after about 2 tanks it started to run lean. Took the saw home and opened the carb and found a clogged screen. Flushed the tank with pre-mix and put everything back together. No problems since.

 

[oakchop]

I prefer leaving my fuel tank most of the way full with fresh non ethonal fuel when parking the saw for more then a few weeks. A little room for expansion and to add a shot of fresh fuel if it sits long. The small amounts of fuel left in the tank and carb tend to dry or spoil more readily then large amounts which retain freshness usually much longer and leave little room for condensation which can cause problems.

I'll keep this in mind. I've always heard drain the tank and run it till it died but this is not ideal in Texas where I'm at. Humidity kills anything that suffers from it. It also assists in mold and we're talking a whole spectrum of molds that grow even in a gas tank apparently.
I do like the low gas method idea. I feel keeping my tank dry caused this mold issue.
Oh and I did swipe my finger in the gas tank and sure enough this super light white film in on the surface along with 50:1 premix non ethanol gas.
some molds can even stand up to petroleum.

This article here (https://www.bellperformance.com/bel...contamination-by-microbes-fungus-and-bacteria)
is all about this mold in gas tanks. although the topic is diesel fluid it's prevalent in chainsaws near oceans or in humid climates too.

 

[oakchop]

I only ran into this once and that was in an old 025 (predecessor to MS250). The tank had some crud in it so I decided to try to clean it out with lacquer thinner. It turns out that the lacquer thinner / mechanical agitation dissolved an oxidized layer on the inside of the tank. Next time that I ran the saw after about 2 tanks it started to run lean. Took the saw home and opened the carb and found a clogged screen. Flushed the tank with pre-mix and put everything back together. No problems since.

yes I know there's something in my gas tank. it's white and feels like a slick chalk paste. I'm reading online that this is white mold that forms in gas tanks and carbs that collect tiny amounts of water (Oklahoma). if you then move that to another more humid topical like region (Texas), then whatever was going on in this saw prior will accelerate 7 fold.
If my issue is indeed mold, I can tell you now gasoline does nothing to it. If it's oxidation of some sort (salt related) then gasoline won't have an effect on it either. It just spreads it around.
One thing that shows it could be oxidation (or mold for that matter) is before I ran the saw I looked at the top of the piston head and it had fresh rust on it. so I know this saw was in some humid conditions at best. before it was shipped. it likely sat in a shed at the Sthil store out back waiting for a buyer collecting water. that's my best guess.
Oklahoma has tons of rain. Since I've had the saw now and ran it the rust disappeared. so it didn't set into the metal, rather the surface which is also bad but not as bad. so being a brand new saw "display model" in a Stihl store, this saw has mold or oxidation in the tank and a fresh, months old rust development on the piston head that disappeared after a few uses. it's now shiny and new looking.

 

[Okie]

I can't afford any downtime. we're relying on firewood for heat.

Same here in this neck of the woods. (about downtime for a chainsaw)
That is just one of several reasons why I also keep a good running back up saw and also repair my own saws and also I keep a good running light weight saw for trimming small stuff, but it's also strong enough to use on 20 inch firewood logs if needed.

Caution: Start learning how to repair your own chainsaws and if you like to tinker and have patience, you will accumulate many. It gets into your blood.

What happened to the OP? (and his 250)

 

[stihltech]

Store empty. if it ain't in there it can't go.bad.

 

[Oletrapper]

The MS 250 has the WORST air filter set up ever and will quickly bypass the filter as the little thin plastic box deforms from the restriction

I have to ask, what does that have to do with the inside of the carburetor? OT

 

[Oletrapper]

Same here in this neck of the woods. (about downtime for a chainsaw)
That is just one of several reasons why I also keep a good running back up saw and also repair my own saws and also I keep a good running light weight saw for trimming small stuff, but it's also strong enough to use on 20 inch firewood logs if needed.

Caution: Start learning how to repair your own chainsaws and if you like to tinker and have patience, you will accumulate many. It gets into your blood.

What happened to the OP? (and his 250)

Good morning all, I have read the entire thread. I smell a troll. Things that jumped out in the OP's posts. Only 10 hours total run time on the saw so he hasn't cut much wood. Rust on top of the piston? Aluminum does not rust!
Just too exact on everything. Everything is perfect. Checked everything that you could possibly check but failed to remove the impulse line and inspect as recommended. They can get hard over time, crack, not seal properly. Found screen clogged in carburetor which in my humble opinion is caused by fuel containing ETHANOL. Anyway, as I said, I suspect a troll. If I am correct, he sure kept everyone busy. LOL
JMHO OT

 

[ZeroJunk]

FWIW, I had a MS362C a few weeks ago that was bogging down and the owner had put some kind of fuel filter in it that the fibers that the filter was made of had clogged up the screen .