MS250 won’t run right.

[Jeffsaw]

Hi, my MS250 starts okay but won’t stay running or idling. It dies when I use the throttle. Sometimes I can keep it going if I pump the heck out of the throttle but it eventually stops.
Not my favourite Stihl. Thanks for any suggestions on how to fix it before I drop it in the metal recycle bin.

 

[ammoaddict]

Have you tried tuning the carb at all?

 

[Jeffsaw]

Yes, but it didn’t change what the saw was doing. I may try some Seafoam.

 

[ZeroJunk]

Yes, but it didn’t change what the saw was doing. I may try some Seafoam.

Go ahead and buy you a new carb for about $45 U.S. , or you may have some luck cleaning the main jet with a wire off a hang tag like StihlTech I think does some time.
Doubt SeaFoam will help you.

Sometimes if you just keep goosing the thing over and over it will clear the bugger. Sometimes.

 

[Vintage Engine Repairs]

You need to share a little more info.

How did you come across the saw?
When did this issue start?
Has it been serviced / tuned recently?
Have you pressure and vac tested it?
How old is the fuel?
Did you buy it in this condition / fault?
Can you upload a video of the symptom?
How are the fuel lines, filter and carb kit?


People hate on clamshells, but they’re fantastic saws, easy to rebuild (no special tools required) and to get parts for. Cheap, don’t rot and are reliable little engines for what they are!

 

[stihltech]

The fix is to diagnose the complete saw. You can just put on a carburetor but what about the rest of the fuel system? Other rubber parts, etc.
I also have a magic wand cheap.

 

[stihl sawing]

I just changed the carb on mine and fixed it. 38 bucks at stihl. you can probably get a chinese one half of that on amazon. i didn't look but wouldn't doubt the one i got at stihl is chinese

 

[SteveSr]

You need to share a little more info.

How did you come across the saw?
When did this issue start?
Has it been serviced / tuned recently?
Have you pressure and vac tested it?
How old is the fuel?
Did you buy it in this condition / fault?
Can you upload a video of the symptom?
How are the fuel lines, filter and carb kit?


People hate on clamshells, but they’re fantastic saws, easy to rebuild (no special tools required) and to get parts for. Cheap, don’t rot and are reliable little engines for what they are!

more info would definitely be helpful. However, this is a classic symptom of a stuck main nozzle check valve in the carb. This is a non-repairable fault and common with Zama carbs. The valve leaks just enough so that it won't idle and then won't move out of the way to let it run at power.

 

[ZeroJunk]

Well, there are at least five different carbs for that saw. One has the needles close together, one has them about an inch apart, one has a single idle speed adjustment screw, and then those also have a version with an extra nipple for a primer bulb. Obviously, if you don't have a primer bulb that solves that. But, if you use the wrong version it will work , but the adjustment holes in the carb housing won't line up.

So, take your carb off and take it to the Stihl dealer, or get the number off the side of it. Partsmart should have the version number beside the part number for your carb.

 

[Old2stroke]

Do you have a lot of experience in tuning a carb? Magic in a bottle is not going to make any difference, a new carb might be the cure but be aware that any replacement carb still has to be tuned even if it's an OEM. If it's a cheap one from China it also has to be taken apart and inspected for correct parts and assembly and still might have hidden faults. Before digging into it, do you know anyone with tuning expertise that can help?

 

[stihltech]

Also may have a bad accelerator pump IF all other parts of say are good.

 

[SteveSr]

I didn't look but wouldn't doubt the one i got at stihl is chinese

There is a BIG difference between a genuine Stihl/Zama carb that happens to be made in China and a Chinese clone / copy from who knows where.

 

[stihl sawing]

Meh. I doubt it. The original one

 

[stihltech]

Many, many companies have factories in China that make products under their quality control. There are also chinese companies making copies of those products under no ones control. Those are the cheap ones. Just buy a couple of those and you may get a good one. Se it the shop quite often now. "I just put this part on it from Ebay cause it was a lot cheaper." Yes it was. but it doesn't work. Try again. And again, etc.
Or, I can fix it with the correct parts.

 

[Jasonrkba]

Sounds like the low circuit is starved. If opening the jet doesn't fix the problem it may be time for service. If nothing has been done id rebuild the carburetor, replace the fuel line and filter. Stay away from ethanol gas..

 

[cookies]

Seafoam is snake oil, it will not repair a clogged carb, cracked hose, failed plug, torn intake boot or a slew of other issues that will cause your symptoms. Pay the local shop and be done with it in a day or two or take it apart yourself after requesting the service info in the beg for manuals thread. Folks in here are good at helping but be prepared to spend real time if your issue is uncommon. My rule on chinese carbs is buy two or three because its a odds game on it functioning, a carb kit is a roll of the dice but I continue to use them before buying a new carb being I am a cheap fker. If the saw is more than a handful of years in age I would replace the fuel pickup hose, filter with oem, rebuild the carb and rinse out the fuel tank then replace the plug and air filter for good measure after checking the intake boot and crank seals for integrity vac/pressure testing.

 

[HarleyT]

Likely the fuel line is cracked badly.

If so, replace it and go through the carb correctly.

 

[Lawless]

My MS250 was never used much because it never ran well and was hard to start hot.

I know it’ll earn me some ridicule but I replaced the carb with this one and it runs flawlessly and starts every time now. the factory carbs are known for the flooding when hot. This one does not have that issue. I now use the saw more than even the pro saws.


https://www.amazon.com/gp/product/B06XWHHGHH/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

 

[stihltech]

The factory carbs are known for flooding when hot? When? Where? Haven't seen that in 40 years. Damaged carbs will. I find them pretty reliable just need to pull quickly after setting to TDC.

 

[stihl sawing]

Damaged carbs will.

then mine came damaged from the factory. mine has always been easy to flood. took it back to the dealer and they say nothing wrong with it. i know how to start a stihl. i have a few of them. stihl dealers generally suck. only found one that didn't think they was the only game in town.