Stihl MS 250 wont start

[fxrtharley]

Hi, my chainsaw has been dependable but now went to use it and it will not start.
The saw is probably 6 years old used a few times a year and I do not use ethanol gas. I am guessing it is now fuel related since I did try to prime and start but the plug was dry: I did not see any cracks in the fuel line and the tank filter looks clean. I know you are not supposed to use starting fluid but I did throw a bit in and put the plug back in but no pop.
I know I have spark but is there a way to add fuel to make sure it will pop and is it worth trying to clean the carb or just find a new one if the carb is suspected? I have tried to rebuild carbs with no success but maybe just a cleaning with aerosol carb cleaner has been known to be all it needs.
Any suggestions are appreciated, I know it is an easy fix, just need to find the culprit before I spend $ on a shop. thanks

 

[atpchas]

Remove the air filter and pour 1/4-1/2 teaspoon of mix down the carb throat. If you get no pops at all from 6-12 pulls it's likely ignition. If it starts but dies after 1-2 seconds, you have spark but not fuel. Search accordingly.

 

[Wonkydonkey]

That’s what I always do, half a teaspoon-ish down the carb throat, you maybe able un click the air filter? . Remember that you’ve put quite a bit of fuel in the crankcase, so I normally put it on the hot start setting first. Then after 4-ish pulls it should fire up and run fast till it’s burnt the fuel in the crank and hopefully pulled some fuel into the carb and upon the 2nd time of doing the same it will have pulled enough into the carb and continue running.
My 660 was the last time it did this to. It fired up 3 times after putting fuel in the carb throat.
So after it wouldn’t pull the fuel through into the carb for it to run properly I tore the carb apart to only find a dry carb it turned out to be a flattened/collapsed fuel line (prolly ethanol related ).

I tried to blow fuel out of the tank through the cap while the carb was off and actually thought it was the fuel filter. Then I found the flat fuel line.

Btw if it starts with fuel in the throat, it could be the impulse line, and having said this i think the 250 has a primer bulb ?. So there’s that to look into

So hopefully for you it’s a simple fuel related problem

 

[Wonkydonkey]

The starting fluid may have evaporated .

That’s f you put it in with the plug was out .?

You really need to get it in the crank (fuel mix)

I guess you need to figure out if there’s any fuel getting to the carb and how far it’s getting in the carb. This may not make much sense just yet. But it helps diagnose it a bit.

Poast up some more questions after the fuel down the throat trick and after looking at the impulse line.

If you need a parts manual to help you etc? Then ray is your man although I,m sure I could magic one up from here or there

 

[hacskaroly]

I know you are not supposed to use starting fluid but I did throw a bit in and put the plug back in but no pop.

I cringe when I hear people using starting fluid...all power and no lube! Next time you can try WD-40 if you have it, there is lube in it and it is ignitable. This is what I use when working on pistons and cylinders or just trying to get a chainsaw to pop.

 

[fxrtharley]

Hello all, thank you for the suggestions so far. I did confirm spark and put a small amount of fuel in the carb and did get it to pop. I am finding what I believe to be fuel actually pouring into the chamber where when I remove the muffler I have to dump fuel out of it.
I did take off the carb and cleaned the best I could and tried to start. There is no bulb so the procedure is to leave the lever on off and pull the rope a few times to prime and then put it on choke. I think when I try to prime, it dumps fuel into the chamber and floods it. I also cleaned it all up and did not prime and pulled a few times and same thing happened. I did check the needle valve and it is not stuck so not sure what meters the priming. Any further thoughts? Since I know I am getting fuel, the only thing left is try a new carb but looking to see if anyone has experienced this. Thanks

 

[Paul Fithian]

I had a similar issue and solved it with a new WT-215 carb. See https://opeforum.com/threads/bernies-ms250-upgrade.29547/page-4

 

[hacskaroly]

when I remove the muffler I have to dump fuel out of it.

Sounds to me that you might be flooded. Typically this can happen when the saw is hot (either from running or hot outside) and you pull too many times with the choke on. This happens when people miss the pop and keep pulling with it choked. You can try putting the saw on idle or fast idle (not choke) setting and give it about 20 pulls. If it was flooded it should fire up at some point and go (may smoke for a few seconds too). I had customers that would run the saw, stop to fuel and try to restart with the choke and end up flooding it out. You definitely get an arm workout!

 

[Wonkydonkey]

Ilwill add . some saws flood easy
If you’ve heard the pop then it should start . If it’s flooding after the pop then maybe your needle screws are set wrong ? Or when you reassembled the carb you’ve put it back together in the wrench it order ? ( gaskets & metering diaphragm?) but I’m not really sure on this .?

If you’ve not put the metering lever spring in properly then the metering lever could open ?

Did you take this bit apart ?

 

[Wonkydonkey]

Heres a typical carb ipl layout for a 250 there are different carbs for the saw
But you should get the idea ?

 

[Wonkydonkey]

After rereading your poast

Hello all, thank you for the suggestions so far. I did confirm spark and put a small amount of fuel in the carb and did get it to pop. I am finding what I believe to be fuel actually pouring into the chamber where when I remove the muffler I have to dump fuel out of it.
I did take off the carb and cleaned the best I could and tried to start. There is no bulb so the procedure is to leave the lever on off and pull the rope a few times to prime and then put it on choke. I think when I try to prime, it dumps fuel into the chamber and floods it. I also cleaned it all up and did not prime and pulled a few times and same thing happened. I did check the needle valve and it is not stuck so not sure what meters the priming. Any further thoughts? Since I know I am getting fuel, the only thing left is try a new carb but looking to see if anyone has experienced this. Thanks

after rereading your poast, pulling with the switch in the off position to prime it is your first problem/mistake,

I always just put every saw to choke position (when cold and or ran out of fuel) till it pops then onto hot start and pull .

I think your find the manual says this as well ?

Page 37

https://cdnassets.stihlusa.com/1625860145-stihl-ms-250-owners-instruction-manual.pdf#page39

 

[Coupe]

Take the spark plug out and put a bit of fuel directly ind the cylinder.
At least if you have spark she should fire ar least. Also take your tank filter
off and preasure test from there and that will also test if you have
any leaks in the fuel lines and carby.

 

[fxrtharley]

Thank you everyone, it helped me pinpoint where to look for the problem. I disassembled and cleaned the carb the best I could but still would not start. Instead of buying a rebuild kit, for the cost of a new carb I just replaced it and it runs great. I have rebuilt carbs before but never had any luck.
Thanks again for your help.

 

[Woodwackr]

The 4 ms250s that I've fixed all had this same problem. Carb rebuild and no more problems.