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

[Lawless]

Saw sounds really lean to me but videos can be deceiving.

Fuel line been checked for cracks?

 

[coffeebrk]

For Pete's sake please get a tach on the saw. OK my rant sorry.

 

[Pioneer]

Make sure you clean your air filter after every cutting session, I have to do it with my 250, the filter will plug up with fine saw dust quickly and make the saw run rich.

 

[Amin_1992]

Hey yall, trying to respond to everyone. Appreciate all the responses.

Fuel lines all look good to me, doesnt appear to be any leaks.

I did use a tach on this haha, tuned for 12k RPM high speed and tried to tune for 2800 RPM at low speed but it kept stalling, so I couldn't get it to run and stay running unless I bumped idle up to around 3600 RPM.

Thanks for the tip on cleaning the air filter, I definitely do clean it often.

Wanted to respond to @4CornersPuddle specifically, thanks for the response. Not going to lie, I took this video back before the carb diaphram was replaced, so I can't remember. However, it seems to behave similarly now even when warmed up, running over an hour. I'm definitely willing to take more videos! I've got her torn apart right now though so want to replace the carb and see what happens first.

When you say "ease up" on a long buck, do you mean pull the bar out and rev it in the air, to get oil built up? I can definitely start doing that. And that's great to know, about backing out a bit and backing off the throttle a bit. I definitely am not doing that, and getting the stalling. Maybe a technique issue on my end? Can I ask, why do you back off and back out? I'll start doing that here on out. Thanks again

 

[4CornersPuddle]

It's not necessary to pull the bar all the way out of the cut, just lift the chain off the wood, keeping the bar in the kerf and the chain turning. When cutting nice green softwood this is completely unnecessary unless, of course, your oiler is not putting out enough oil. It can be a real help in dry hardwood or pitchy pine such as the pinyon we have here in the southwest.

 

[Kenskip1]

Here is my .02cents worth. After a full power burn unburned mix accumulates inside the crankcase. This is now flooding or exceptionally rich and slowing the saw down. What causes this? Worn rings. In a normal position, all is well and saw runs normally. Ken

 

[SteveSr]

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.

That chain is duller than the dirt that dulled it!

Dying out like that is a sign that the saw is too rich coming off of WOT. May also be old gas. Get some fresh from the pump non-E gas and make a new batch of 50:1 mix.

1. Clean/replace air cleaner. SOFT paint brush from outside followed by non-chlorinated brake cleaner from the inside.

2. Remove and burn the spark screen from the muffler with a torch.

3. Now you are ready for carb tuning. Set the "H" to full CCW limiter stop.

4. Set the "L" to 1-turn out from lightly seated. Should be printed on the AF cover. Leaning out the "L" slightly (CW) may help the idle recovery issue.

5. If this doesn't improve the running put a new OEM (ONLY) kit in the carb or replace the carb as a last resort.

Keep in mind that a new carb will need to be tuned properly and then the "H" limiter punched down.

 

[user 74409]

A bad primer bulb will cause the stalling symptoms you are experiencing. Carburetor will suck air and engine will stall out. To test, you can plug line between primer bulb and carburetor. The primer bulbs do not age gracefully and it is due for replacement.

 

[Amin_1992]

It's not necessary to pull the bar all the way out of the cut, just lift the chain off the wood, keeping the bar in the kerf and the chain turning. When cutting nice green softwood this is completely unnecessary unless, of course, your oiler is not putting out enough oil. It can be a real help in dry hardwood or pitchy pine such as the pinyon we have here in the southwest.

Thanks for this, I'll remember this going forward. So this helps the bar stay oiled? I suppose it has nothing to do with stalling?

 

[Amin_1992]

Here is my .02cents worth. After a full power burn unburned mix accumulates inside the crankcase. This is now flooding or exceptionally rich and slowing the saw down. What causes this? Worn rings. In a normal position, all is well and saw runs normally. Ken

Hoping this isn't the case but very well could be. Saw is nearly 2 decades old

 

[Amin_1992]

A bad primer bulb will cause the stalling symptoms you are experiencing. Carburetor will suck air and engine will stall out. To test, you can plug line between primer bulb and carburetor. The primer bulbs do not age gracefully and it is due for replacement.

Thanks for the suggestion pal. So to test, plug the line between carb and bulb, and run her and see if the issue goes away? I'll definitely do that

 

[Dr_Anon]

I would test the coil. Anytime I get voodoo problems like this it's often the coil. By "test" I mean try a different coil. Sometimes they only short in very specific circumstances and they'll test fine on the bench. I'd also try adjusting the high speed mixture screw.

 

[HarleyT]

Looking at your out of place av mounts/plugs, I would check the impulse line and intake boot. The impulse line is notorious for pulling off of the orange nipple, and an av mount problem would enhance that. Also hard on the intake boots.

 

[coffeebrk]

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.

I think you still have a carb issue.
You could:
1.Rebuild current carb completely
2.Obtain used Stihl carb and put a kit in
3.Purchase a Chinese carb and install it

 

[Amin_1992]

Woops, noticing I missed some responses. Sorry, page loads strange on my phone.

That chain is duller than the dirt that dulled it!

Dying out like that is a sign that the saw is too rich coming off of WOT. May also be old gas. Get some fresh from the pump non-E gas and make a new batch of 50:1 mix.

1. Clean/replace air cleaner. SOFT paint brush from outside followed by non-chlorinated brake cleaner from the inside.

2. Remove and burn the spark screen from the muffler with a torch.

3. Now you are ready for carb tuning. Set the "H" to full CCW limiter stop.

4. Set the "L" to 1-turn out from lightly seated. Should be printed on the AF cover. Leaning out the "L" slightly (CW) may help the idle recovery issue.

5. If this doesn't improve the running put a new OEM (ONLY) kit in the carb or replace the carb as a last resort.

Keep in mind that a new carb will need to be tuned properly and then the "H" limiter punched down.

Ha, chain was freshly sharpened by yours truly actually! It threw perfect thick shreds so seemed OK to me. I'd believe it is too rich after WOT and agree with you, based on the rich smell it produces when I restart it. I'm using fresh non ethanol fuel now, and in this video was using TruFuel.

1. I clean the air filter in a similar way often, not the issue here.
2. Spark screen is clean as a whistle.
3. I've tuned the carb every which way. I've done it per the label on the side, per instructions from the Stihl service manual, using a tach, trying it by ear with the help of Youtube videos from Steve's Saloon and Donyboy, none have worked... it's beyond a tuning issue.

4. Will be replacing the entire carb just to get beyond this issue!! Thanks for your input.

I would test the coil. Anytime I get voodoo problems like this it's often the coil. By "test" I mean try a different coil. Sometimes they only short in very specific circumstances and they'll test fine on the bench. I'd also try adjusting the high speed mixture screw.

I'll give that a shot! Could even buy a cheapo off Amazon maybe just to check. I'm replacing the carb first and going from there though.

Looking at your out of place av mounts/plugs, I would check the impulse line and intake boot. The impulse line is notorious for pulling off of the orange nipple, and an av mount problem would enhance that. Also hard on the intake boots.

Oh man, I'm starting to feel judged here! Joking ha. What do you mean out of place mounts? They all appear intact and normal to me but maybe I'm missing something here. Impulse line is luckily attached and appears intact. The rubber boot between the carb and engine looks OK too just shining a light down... but I plan on testing that and the impulse line after I replace the carb, by spraying some starting fluid near it and seeing if RPMS jump at all. Thanks

I think you still have a carb issue.
You could:
1.Rebuild current carb completely
2.Obtain used Stihl carb and put a kit in
3.Purchase a Chinese carb and install it

Thanks for the input. I tried rebuilding the carb last time and royally bugged it up. I'm not good with teeny parts haha. I went for option 4 and bought a brand new OEM Stihl carb instead, it was only around 12 bucks more than the chinese ones online. Funny enough, my main Stihl dealer quoted me $50.99 for an OEM carb, and said it would be 3 weeks out unless I paid something like 20 bucks more for 3 day shipping! Called the other Stihl dealer nearby that I've never been to, they quoted me $30.99 and would be here in 3 days, no shipping charge... I didn't realize that Stihl dealers can decide their own price / markup.

 

[HarleyT]

The impulse line goes from the block to a plastic nipple on the backside of the orange handle housing, and is pulled out easily, especially when stretched by pressure is applied in the cut. The a/v mount plugs look screwy, as the mounts are not in their proper position, which usually means heavy yanking/pulling in the cuts. So it is worth a look.

 

[Amin_1992]

Hmm what do you mean by screwy though? Like one is sticking out a bit, one is pushed in a bit? I'll give it a look. Impulse line is plugged in though. Anyway to "reset" the mounts? Thanks pal

 

[HarleyT]

The saw acting differently when in the cut usually means something.

 

[HarleyT]

Hmm what do you mean by screwy though? Like one is sticking out a bit, one is pushed in a bit? I'll give it a look. Impulse line is plugged in though. Thanks pal

It is hard to see. You can see it with the starter off.

 

[Amin_1992]

I've gotten a ton of suggestions here so far which is great, lots of things to check.

1. I'll obviously start with just replacing the entire carb since I've already got the old one out, and new one on the way.

2. If that doesn't fix it, I'll start checking all the different fuel lines, purge bulb, intake boots, impulse line, etc... I suppose I can check by spraying starter fluid near them while idling and listening for a jump/drop in RPM right?

3. If those all appear OK, well I'm at a loss - only other suggestion was worn rings. Might be time to just sell this thing on CL for $150 or something and invest in a new MS261!!