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

[HarleyT]

If it is pulled loose, it retains it's shape and stays roughly in position, and the saw will run a bit. But when put in a cut, the line is pulled away from the nipple.
It is hard to visually inspect. I circled it in black.

 

[Amin_1992]

Thanks for sharing this. I'll try to give it a check. Could I prop the saw on my work bench and put pressure on the bar, to simulate it moving/cutting? See if the impulse line actually moves out of place.

I did push a screwdriver in there gently and push on the line. It didn't budge. Appeared to be attached on both ends.

Would spraying starter fluid near that change RPMS if it is loose/detached?

 

[HarleyT]

I use wd-40, if you hit a leak, the engine will change.
Have you tried richening up your low speed screw? You might have to pop the limiter off.

 

[Amin_1992]

Ok good to know about WD40, didnt realize that would work here!

Yup, no need to remove limiter as I am able to adjust both rich and lean to the point of stalling. I've got the full swing, and i've tried every sort of adjustment and tweak on this saw - literally dozens of recorded combinations and no luck

 

[SteveSr]

Ok good to know about WD40, didnt realize that would work here!

Yup, no need to remove limiter as I am able to adjust both rich and lean to the point of stalling. I've got the full swing, and i've tried every sort of adjustment and tweak on this saw - literally dozens of recorded combinations and no luck

If the limiter caps have been removed the screw settings printed on the saw or in the manual are out the window. You will need to tune based on engine performance.

That black plug says that the saw is too rich from a carb or tuning issue.

The new carb should come preset but without the limiters punched down. Try running it like that first.

 

[fixinsince69]

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

Maybe low compression?

 

[cookies]

Don't be intimidated about changing piston rings, its quite simple once you get over the fact your taking it fully apart. Just make sure you really clean the saw before you open the engine. A tube of permatex ultra black, crank seals and new rings and a couple hours to perform gods work while enjoying some alcoholic beverages and its over before you know it.

 

[Amin_1992]

Hey ya'll, just wanted to post an update. Finally got the new carb in from the dealer. It matched the old one and I installed, and at the same time installed a new fuel filter.

Saw took a bit to start up. Not sure if a new filter needs broken in for a minute? Or a new carb even?

I had always read that OEM Stihl carbs don't need adjusted from the factory. Well, mine did. Low and High were pretty much spot on, but the idle was too high - idled at around 4400 RPM. I lowered that to get it down to 3200 RPM.

Seems happy, though I'll admit I dont have any wood to cut into to really test it out! I had one log left, so just started making slices into it. If I'm cutting through at full throttle, and let off the throttle with the bar in the log still (touching wood) the RPMS still dropped a bit and the saw did stumble. After about 3-4 seconds, idle climbed back up. It didn't stall though - but then again, like I said, I only cut with it for maybe 10 min or so.

Can I ask you guys, is it normal for the idle to drop after cutting into a log at WOT? Then to climb back up? I think somehwere here mentioned something about it. But I'm curious.

I did test the fuel vent, it works. I sprayed carb cleaner around all the hoses and connections - didn't change RPMs, so don't think I have any leaks.

I also noticed that before I put her away, idle seemed to be moving up and down a bit - going back and forth between around 3200 RPM and 3800 RPM, back and forth, without touching her. Again, maybe braking in the filter/carb? IDK.

I will have to wait for the next tree to come down in a few months to really test her out. We'll see then but hopefully all is good for now...

 

[SteveSr]

Hey ya'll, just wanted to post an update. Finally got the new carb in from the dealer. It matched the old one and I installed, and at the same time installed a new fuel filter.

Saw took a bit to start up. Not sure if a new filter needs broken in for a minute? Or a new carb even?

There is no breaking in. This is normal the fuel system was dry

I had always read that OEM Stihl carbs don't need adjusted from the factory. Well, mine did. Low and High were pretty much spot on, but the idle was too high - idled at around 4400 RPM. I lowered that to get it down to 3200 RPM.

How did it run before you adjusted the H & L?
Which way did you adjust the H & L?

Can I ask you guys, is it normal for the idle to drop after cutting into a log at WOT? Then to climb back up? I think somewhere here mentioned something about it. But I'm curious.

This is generally an indication that the H is too rich. The leftover gas temporarily richens the idle causing the RPMs to drop or the saw to possibly stall.

I did test the fuel vent, it works. I sprayed carb cleaner around all the hoses and connections - didn't change RPMs, so don't think I have any leaks.

You still may have leaks. The remaining candidates are the crank seals and engine pan.

I also noticed that before I put her away, idle seemed to be moving up and down a bit - going back and forth between around 3200 RPM and 3800 RPM, back and forth, without touching her. Again, maybe braking in the filter/carb? IDK.

Erratic idle is often caused by leaking crank seals. What does the idle do when you turn the saw recoil up or recoil down? This shifts the crank slightly and can expose seal leaks.

 

[burnses]

i skimmed though this post and by now you probbibly have fixed it or are on your way to...what you originally described is a slightly rich low speed setting but to rich a high setting can do it too. Assuming imbulse and all the rubber stuff is ok as described above this is what i think is going on. When in a cut you are at wot and full load and the max amount of air and fuel is getting into the engine. You shut the throttle abruptly and the remaining unburnt fuel and fuel from the idle circuit try to flood the engine...thats the rpm drop...and it recovers to idle sometimes...fine tune of low speed and idle speed and cure the issue..possibly generally a saw is not run in that way but if the problem was not present previously then something must have declined. The saw has some time on it so rings and crank seals might be causing some issues...alos carbon accumulations in the combustion chamber ex port and muffler my make it harder for the saw to clear it self and recover to idle during a rapid return to idle after full load.....

good luck
the can

good luck

 

[Pat Burton]

Maybe low compression?

I had exactly the same issue. 90 lbs instead of 155 on an old 025. Wet test brought it back to 150. It still produced decent cutting power but would stall when returning to idle. Same issue with a 455. Someone straight gassed it. Low power and die out.

 

[Amin_1992]

Hey all I really appreciate you still responding to this. Pulled my saw after storing for a few months and cut into a log for about 15 minutes. Seemed to cut through fine with no bogging or stalling, though sometimes this wouldn't rear it's head until the saw was good and warm 1+ hour into working...

I plan on getting back into firewood processing in the next month or two so will really put it to the test, and if I continue to have a problem I will go back to your responses and use that to help me further troubleshoot.

Means a lot thanks all!