Stihl MS250, stalls out when releasing throttle, but ONLY when bar in log

[Amin_1992]

Hey guys, I am totally stuck at this point and decided to drop my Stihl MS250 at the local shop to have them give it a shot. Wrote them a detailed note and they are 2 weeks out, but figured I'd post here in the meantime to get you all's opinion.

This issue has me baffled and annoyed to no end. The saw runs beautifully despite being nearly 2 decades old, except for this one issue that has happened for a while now.

When cutting into a log, at full throttle, and then releasing the throttle with the bar still in the log, the saw will stall out. When it doesn't stall out, the idle drops very low, as if it's about to stall. After about 5-10 seconds, if it doesn't stall, idle RPMS climb back up to where I have them set.

This only happens when the bar is still in the log, touching wood against the chain. Cannot replicate it by revving in the air and letting off the throttle.

Starts perfectly, will sit there an idle all day long. Usually starts on just 1 pull. But when it stalls out like this, restarting it takes like 6-8+ pulls.

I've tried everything. The obvious has already been done - spark plug, air filter, tuning the carb screws - with no luck. I even replaced the clutch, as a user on here way back thought maybe it was the clutch sticking. Their theory made sense - chain touching log, so if clutch is sticking then the stopped chain will cause the engine to stop turning too. However, new clutch that is totally clean doesn't help. I also inspected all the fuel lines and as far as I can tell, no cracks or leaks. They all seem pliable and when pressing the purge bulb I don't see any fuel or bubbles or anything leaking out.

I actually had it at the shop a few months ago for an unrelated issue, they tore apart and cleaned the carb and changed the diaphragm, and it actually ran quite well for a few weeks before I put it away. Month or so later, it's back to this bull.

Any ideas? I'm about at my wits end and just going to sell the saw and buy a new MS261 or something. Let me know what yall think, thanks

I actually got a video of it stalling out. Check it out: cutting into log at full throttle, release throttle part way through, saw dies.

 

[cookies]

I'd throw a new carb on it, sounds like its flooding out. Im not a betting man but if I was I'd bet the check valve disk is scored or needle spring is weak/leaking.

 

[Amin_1992]

I'd throw a new carb on it, sounds like its flooding out. Im not a betting man but if I was I'd bet the check valve disk is scored or needle spring is weak/leaking.

Well that's easy enough, I had another person on another site tell me it was the carb too. Great to know. Can I ask you, any way to easily identify which carb I have? I just made a post about this on the site too, but it looks like the MS250 has 17 different carb options! I have my serial number, 269446980, wasn't sure if I could look it up with that?

 

[cookies]

There are numbers/letters on the side cast into the body. Use the search bar to find the beg for manuals thread and ask for the IPL and service manuals. There may have been 10+ revisions of that carb but any should work with minor efforts.

 

[coffeebrk]

How sharp is your chain? I think it is fuel/carb also. Do you inspect or replace fuel filter?

 

[Amin_1992]

Thanks guys for the response. I called my dealer and gave them the serial number. They didn't seem sure which carb went to it either but recommended the C1Q-S92E. On my carb, I have stamped ZAMA and S92 620A. Googling that number doesn't pop up with anything though...

So any carb will work? Does it matter mine is one of the easy starts?

BTW chain is sharp and fuel filter changed yes

 

[Chevboy0167]

http://www.zamacorp.com/tclist.html?cnum=C1Q-S92
https://www.ebay.com/itm/3838254422...pbcm/M=|tkp:Bk9SR5ioofCOYQ&LH_ItemCondition=3

 

[Amin_1992]

Thanks for posting, looks like what they recommended. But are all of these different Zama carbs interchangable? My carb this engraved on it:

S92
620A

I can't seem to find a match anywhere for it...

 

[Chevboy0167]

Prefix is C1Q. This is the series, I think. The last numbers and letters I personally don't know but the "A" may be the first revision of that series.

C1Q-S92

If ya look a bit closer on the carb body, you will see a giant C1Q somewhere I believe.

 

[Amin_1992]

Thank you Chevy Boy, I'm thinking youre right. So my old saw had the A revision, and theyre now on the E revision. Makes sense! I'll order the C1Q-S92E and let you all know how it goes in a week. Thanks!

 

[samaritan]

You of course changed the bearing on the clutch? Check its compression too! and spark-be sure its strong and blue white clr

 

[Amin_1992]

You of course changed the bearing on the clutch? Check its compression too! and spark-be sure its strong and blue white clr

When you say bearing, do you mean the little needle cage? If so, yes I did. Compression is good. I seem to have good spark as she starts up instantly and idles just fine otherwise.

 

[samaritan]

When you say bearing, do you mean the little needle cage? If so, yes I did. Compression is good. I seem to have good spark as she starts up instantly and idles just fine otherwise.

Yes, that's the one. Does the coil feel hot when this happens? If its none of these, the only thing left is the carb I guess, I have pulled out some of my hair with problems like these. lots a luck

 

[Amin_1992]

Thanks for replying. I mean, the coil feels hot but feels normal to me? As hot as the rest of the saw. We'll see how the new carb does - I'll report back this weekend!

 

[samaritan]

Thanks for replying. I mean, the coil feels hot but feels normal to me? As hot as the rest of the saw. We'll see how the new carb does - I'll report back this weekend!

ok

 

[samaritan]

ok

Damn, I just had a brain fart, you say it stall when releasing throttle with chain in log? sorry, but why release throttle with chain in log, why not pull it out first? Is the idle fast enough, fast, but not moving the chain?

 

[Amin_1992]

Damn, I just had a brain fart, you say it stall when releasing throttle with chain in log? sorry, but why release throttle with chain in log, why not pull it out first? Is the idle fast enough, fast, but not moving the chain?

Hey, so I've got an 18" bar but I am oftentimes cutting into very large logs, usually 18-26" in diameter. My saw is definitely not ideal for this but it's a great saw and I've learned to be patient and not rush the cut. However, because of this I'm oftentimes stopping for a moment midway through the cut. Likewise, when I'm felling trees, I'm not going full throttle the whole time. I'm just an amateur, so I'm often stopping while doing a notch and as a result, the saw stalls out. Not ideal when a large tree is midway cut!

If I pull the saw out of the wood before letting off throttle, or I blip it to slowly bring the RPMs down, no stalling. But I shouldn't have to do this.

 

[camel2019]

Hey, so I've got an 18" bar but I am oftentimes cutting into very large logs, usually 18-26" in diameter. My saw is definitely not ideal for this but it's a great saw and I've learned to be patient and not rush the cut. However, because of this I'm oftentimes stopping for a moment midway through the cut. Likewise, when I'm felling trees, I'm not going full throttle the whole time. I'm just an amateur, so I'm often stopping while doing a notch and as a result, the saw stalls out. Not ideal when a large tree is midway cut!

If I pull the saw out of the wood before letting off throttle, or I blip it to slowly bring the RPMs down, no stalling. But I shouldn't have to do this.

It’s 2 stroke full throttle or no throttle

 

[HarleyT]

Looking at the saw, and what can be seen of the av mounts, I would look closely at the intake boot and impulse line, as well as the fuel line. They are well known for developing cracks.

 

[4CornersPuddle]

Video posted of your saw makes saw sound really doggy. RPMs very low. Chain appears to stall at one point. MS250 should rev way higher than this. As you first hit the throttle, the saw doesn't appear to catch and rev immediately.
Was the saw warmed up when you made that video? From your video, we can't tell how well carb is adjusted.
Are you willing to make more video with plenty of varied examples of your issue?
Plenty of us who have logged professionally, including Buckin Billy Ray, will ease off on a long buck for a moment to allow a little extra oil to build up on the chain on a full bar length cut.
And, despite having made my living now for 50 years running all sorts of power saws, I still don't simply release the trigger in a cut while under full load. I always back out and back off slightly.
Hope some of this can help you.