Stihl MS 250 problem, fuel starvation? Help!

[bernithebiker]

Hi - I have an MS250 which is only 2 years old and has only seen moderate use.
It has developed a problem whereby it is hard to accelerate the engine up to working speed - it makes a noise like it's running out of gas - it kind of sucks hard but struggles to build up revs. So to get to cutting speed, I have to kind of coax it up with little throttle blips, but even when it is running at full speed it is down about 10-20% on power.
If I open the throttle too fast from idle, it often just cuts out.
What I have checked;
Fuel strainer in tank - looks pretty clear to me
Spark plug - seems OK
Air vent next to carb - took this apart - it has a kind of diaphragm inside - didn't look dirty.
Air filter = clean
carb - took off and cleaned a bit, but cannot really get inside - just took off the top and bottom covers to expose 2 black rubber seals, and let the fuel escape. That's all I could do.
In fact, after that carb dismount, and air vent clean, the saw DID run fine for about 2 minutes, but then went back to it's old tricks.
I've exhausted all my ideas...can anyone help?
Would be very grateful!
Thanks!

 

[Lakeside53]

Check your fuel hose very carefully... best way is to fish it out of the tank with a hooked wire, remove the filter, and pressure test it back to the carb. A tiny crack can suck air, and sometimes not leak gas.


I assume you have checked your exhaust screen, and your carb settings?

 

[bernithebiker]

thanks....

Thanks Lakeside.
I did notice that the fuel line that goes directly from the tank to the carb has small 'perish' cracks where it bends, but these are small and don't appear to compromise the pipe.
Exhaust screen, no, I guess that's easy? Just unbolt the exhaust element and clean it out? (This is a European model, not US, not sure if that makes a difference or not).
Carb settings - I have never touched them so unless they moved by themselves then it can't be that. But I could try resetting them and seeing if that helps.
One more thing - it is harder to start than normal too, and doesn't like choke at all. I can often only start it by pulling like crazy with no choke.
The plot thickens....!

 

[buck futter]

what color is your plug?


Check/remove your muffler screen. I say remove it, there is still an internal baffle and the louvres to stop crap from getting in there and arrest sparks.

Buck

if it was a fuel line you may also have problems with your idle quality.
You may be a little lean on the low side. try an eigth of a turn in on the low jet and see if it helps. you may need to raise your idle.

 

[1953greg]

"You may be a little lean on the low side. try an eigth of a turn in on the low jet and see if it helps. [/QUOTE]

buck, uh, i think that would be out, as counter clockwise

 

[buck futter]

your right of course, brain fart.

 

[Lakeside53]

..and if that hose has little cracks, ditch it...

 

[bernithebiker]

pics

thanks alot for the help so far.

I took the exhaust off - it is just one big unit that splits in half. Inside it was nice and clean, light brown, no major sign of coking anywhere. There was no screen as such inside, just a perforated sheet of metal (large holes, 10 maybe). All clean. Maybe a spark arrestor is a requirement for the US only.

Hopefully in the pictures you can see the fuel pipe coming up from the tank into the carb. It does have a few small cracks in it. This may be the problem. When I push on the manual fuel pump blister, I can no longer get it to fill nice and hard with fuel, it just fills a little, maybe 20%. So I think my prob. is definitely fuel supply related.

I will change this fuel pipe - anyone know a good Stihl parts supplier?
Also see photo of spark plug, colour looks OK to me.
Thanks!

 

[belgian]

I had to change the fuel line last week on my 028s too, because of cracks (and leak). Local stihl dealer had it in stock and cost me about 4 euro. No biggie.

 

[chuckiehow]

We run nothing but 025 - 250s in our logging ventures and have found that the newer one port carbs are trouble. A dealer told me it's better to throw them away than to rekit them. Still, I take them apart and use compressed air to clean them up with varied results. Prefer the two port carbs.

On the more difficult side, we're aware of a couple local saws that have had bad crankcase seals. They'll run temporarily (seconds) and then accelerate and die....restart...die....etc.

Recently after changing the coil, sanding the flywheel, changing filters etc. etc., I found the only problem with one 025 was a good looking sparkplug that wasn't so good.

Although I've never had a plugged muffler, I have had fuel lines cracked but it's usually the carb needing cleaned or reset. Start with the simple things first.

 

[bernithebiker]

thanks!

So as a temporary fix, I put some Araldite epoxy glue onto the fuel pipe where the cracks are.
I only got the chance to use the saw for 5 minutes just now, but it seems pretty good, no more starvation, so as long as it stays like that, it should be OK.
Just need to find a new fuel line now, and hope it's not too tricky to fit!
Thanks for all the help, it's great to be able to share info like this - my area of expertise is bicycles - if anyone wants detailled help on them, I'm only too glad to help!

 

[Bermie]

..and if that hose has little cracks, ditch it...

Ditto - I've had two hoses look like this on my 021, both times they were the culprit. Do what the man says!!

 

[Lakeside53]

We run nothing but 025 - 250s in our logging ventures and have found that the newer one port carbs are trouble. A dealer told me it's better to throw them away than to rekit them. Still, I take them apart and use compressed air to clean them up with varied results. Prefer the two port carbs.

.

If you clean them in an ultrasonic cleaner ($60..), they come right about 99% of the time. I don't even blow them out. Also, I'm pretty sure that all the 250 carbs have gone back to 3 screw adjust for the past few years.

 

[windthrown]

Best advice...

Check your fuel hose very carefully... best way is to fish it out of the tank with a hooked wire, remove the filter, and pressure test it back to the carb. A tiny crack can suck air, and sometimes not leak gas.


I assume you have checked your exhaust screen, and your carb settings?

Chances are that if the saw has not been messed with, it could be cracked fuel line. Our 290 did the exact same thing a few months ago. I fished the fluel line out of the tank, but it looked fine to me. Stihl did not run right though, and finally it quit starting completely. The Gf took it onto the Stihl dealer and he said it was a crack in the fuel line, and a no-brainer fix. He charged her $10 total and had it fixed overnight. New fuel line. Worked like a champ again and stihl working fine.

 

[dingo]

fuel hoses

We have had trouble with two of our 385XP's fuel hose also. Seems like they are like dry rot. It's the same thing I have seen on a 79 Chrysler that had ethonal put in the tank when ethonal first came to the stations.

 

[chuckiehow]

If you clean them in an ultrasonic cleaner ($60..), they come right about 99% of the time. I don't even blow them out. Also, I'm pretty sure that all the 250 carbs have gone back to 3 screw adjust for the past few years.

You're correct; they have gone back to the 3 screw carbs.
Sounds like I should get some of that spendy cleaner too.
I've never thought that the needle and seat ever looked like it needed replaced but a good blow of air quite often fixed my problem. Diaphrams can be restored by soaking in brake fluid overnite.
Thanks for the tips.