Stihl MS261 cutting out when chain break engaged

[en_fuego]

Hey all, I've been reading through some other posts about this issue, but I'm still having problems. I supervise a crew that's using 6 MS261 saws and we tend to have this recurring issue.

The saw typically runs fine when the chain break is not engaged. However, upon engaging the chain break the saw starts to run poorly. The tone of the engine changes and it begins to run roughly, eventually cutting out. The saw will typically restart easily but dies unless chain break is disengaged.

I used a Tachometer to see if this was really true about the engine sounding different. When the chain break is disengaged it idles fairly smoothly between 2800-2900 RPMs (factory is 2800 low, 14000 high). When ENGAGED, the idle jumps around greatly between 2700-3000 RPMs.

I went through all of the basics:

replaced and lubricated needle bearing
replaced clutch (one of the saws did have a damaged clutch spring, which was replaced and issue persisted. Clutch plate that sits on top of worm gear also replaced in this one because it wore weird due to clutch break)
replaced drum
replaced sprocket


We clean and maintenance our saws EVERY TIME they are used, so this shouldn't be an issue of neglect or user error. This issue has happened across 3 of our 6 saws. We also use 6 MS261 saws when we are working with another organization and it occurred on 1 of these saws as well. When we use our older MS260 saws we have never had an issue like this. These saws are used fairly heavily, around 25-30 hours per week, sometimes more. The only thing I can think of is the carb is possibly dirty. Before I go down that road of removing the carbs on 4 saws I wanted to get some feedback. Thanks!

 

[rd35]

Based on your description, it sounds almost like there is an electronic rev limiter that is activated by the chain brake handle. I did a quick search and could not find anything about a feature of this type on the 261, but I would love to know. Hopefully somebody who really knows this saw can jump in and tell us the story!

 

[en_fuego]

I have had issues with the MS261C and its computer causing issues, so that's something I should research more on this saw. Thanks!

 

[nmurph]

If the is the regular carb saw, add some L (turn it counter-clockwise) and adjust the idle.

 

[HuskStihl]

+1, the L jet is lean, and you have the idle screw turned down to compensate. The brake adds a little resistance and the saw bogs

 

[redfin]

What am I missing? If the chain is not moving at idle with the brake off the crank is spinning in the drum bearing. Only difference I can see is if the springs are weak and catching the drum with the brake on.

 

[Bilge Rat LT 20]

The clutch drum bearing may be binding the crank when the brake is applied. The drum may be pulled offline of the crank with the brake band.
Check the bearing, crank stub, and clutch drum bore.

 

[HuskStihl]

I feel there is always a little play in the clutch, even at RPM's under frank spinning, and the brake takes that away. I done use it much, but mine always sound a little different with the brake on.

 

[Bilge Rat LT 20]

The clutch drum is locked by the brake, it may be binding on the crank loading the motor. The clutch shoes, springs etc are not binding.

The drum itself when brake is on may be loading the crank/motor

 

[en_fuego]

Thanks so much for all of the responses. I'll start with enriching the L, and adjusting the idle. I'll report back when I give it a shot

 

[dsell]

Maybe the crank bearing and seal is going bad on that side.

 

[en_fuego]

Update - Adjusting the L and idle on one saw seemed to fix one of the 3 (I also found a weird drum on one which explained why the guy was chewing through worm gears). It smoothed out the Idle on another saw which was idling rough with chain break engaged, however it still shut off regularly when engaged. I'll try to dive a little more deeply into the other suggestions. One of the saws will ONLY start when the chain break is off, and the idle drops almost 600 RPMs when engaged.

 

[Chainsaw Jimbo]

My 261 C-M started to shutoff when the brake was applied. After a few hours of tinkering and swapping parts with other 261's, the clutch drum was the culprit. When swapped with a new one, ran fine with brake on. It was slightly rougher/scored on the inside......

 

[HarleyT]

You should replace all of the clutch springs, and not just one.

 

[TreeswingerPerth]

I had this problem with mine , clutch drum was the culprit . It was causing the needle bearing to wear out prematurely , it's a common occurrence with them .

 

[HarleyT]

I had this problem with mine , clutch drum was the culprit . It was causing the needle bearing to wear out prematurely , it's a common occurrence with them .

What, out of round???

 

[TreeswingerPerth]

Yeah , they seem to go oval , was advised to change from a rim to a spur .

 

[HarleyT]

Yeah , they seem to go oval , was advised to change from a rim to a spur .

What would that do?

 

[CR888]

My 261 C-M started to shutoff when the brake was applied. After a few hours of tinkering and swapping parts with other 261's, the clutch drum was the culprit. When swapped with a new one, ran fine with brake on. It was slightly rougher/scored on the inside......

Spot on. IME if the springs are in good order & working properly the next thing I'd check is the clutch drum. The drum is a 'wear item' and needs replacing when worn. You need to take it off & check for a lip/step on the inside. Tree service guys constantly using the brake and stop/starting probally go through drums fastest.

 

[TreeswingerPerth]

What would that do?

Apparently the drum that comes on them goes oval , here in the UK the dealers tell you to switch to a spur and that's supposed to be the end of your problems.
I did this after changing 4 bearings , then sold the saw and bought a Husky 560xp , that was the best cure I found for the 261 .