Stihl 261s Scoring Pistons

[ladylake]

 I have lots of Echo saws that run as good as any per cc.  They need the muff opened up a little and tuned good.  Steve

[Air Lad]

I've been running my trimmer at half throttle for 30years and it still works great.  Maybe its how they are tuned, I'd bet a little rich low helps, plus a little rich on high also. Too many now days are tuned on the edge of being lean, for sure the auto tune machines as they need to get by the EPA as they're sent out . Steve

On that, I was using my old (29yrs)Kawasaki,ex council whipper snipper yesterday. The thing is, I like to run 1/2 throttle at times also but it occurred to me that this machine has the old motorcycle round slide type carby. Mabye they have better oil distribution at medium revs compared to modern carbs

[mike_belben]

Slide carbs meter the midrange by the taper and depth of the main jet needle so you can dial in a safe A/F ratio for the load.  Granted ya gotta actually tune them for the conditions.  

Anything thats only got high and low adjustment generally isnt gonna be ideal in the middle.

[JaredR]

Do chainsaw carvers use full throttle all of the time and have a full load? Is it expected behavior for a brand new product to fail this easily? Less than 5 hours of actual run time and only a 3rd of that at half throttle. 

[Ianab]

It's a known problem. When you combine the low oil ratio, an already lean mix from the factory, lower revs giving less cooling, and a bit of bad luck.... I bet it's possible to kill a saw in one tank of gas. It's only got to run too lean for a few minutes, overheat once, and the damage is done. 

Like the guys mention, 2 stroke motorbikes have a more sophisticated carby, because they are expected to be able to cruise at 1/2 revs / 1/2 throttle all day. 

It can likely be compensated for by using a bit more lube and re-tuning the carb so it's slightly rich. But I think how the saw is being operated is the main issue. The "treat it like a light switch" comment is good advice. If you try and hold a light switch 1/2 on, it will soon burn up too. 

The problem may not occur with every model of saw, but that's more good luck than anything else. 

[Al_Smith]

You really can't compare a slide carb like an old Amal with a Tillotson carb on a chainsaw .If you really look at a Tillotson on a chainsaw it is in essence a mechanical fuel injector .It has to be to be able to run in all positions .
Some real old chainsaws had float carbs but the positions were very limited where they could be used on . 

[farmfromkansas]

I had an 026 and the cylinder scored.  The dealer told me the 260's run faster than the 290's and have a lot of trouble with scoring. Heat builds up at higher speeds. The 290 I bought years ago has been nearly trouble free, so just run it and the 250. Helps to trade off on your saws to avoid overheating.

[mike_belben]

Do chainsaw carvers use full throttle all of the time and have a full load? Is it expected behavior for a brand new product to fail this easily? Less than 5 hours of actual run time and only a 3rd of that at half throttle.

No, thats pretty sad.  

[Al_Smith]

What your dealer failed to tell you about the 024's and 026's  is the fact they came with three different mufflers .Standard ,quiet and real quiet . 
I have an 024 that was in the dealers dead pile,slightly cooked piston .I never did one thing to it except attack the muffler and it runs just dandy ..The guy who  walked out after a trade in ended up with a 290 .He really didn't know any better. 
These things are made to run .However if you hold all that heat in with a restrictive muffler you're bound to bind them up eventually .They are not that loud with a worked over muffler but you certainly would not run them in your garage .   

[JaredR]

It's a known problem. When you combine the low oil ratio, an already lean mix from the factory, lower revs giving less cooling, and a bit of bad luck.... I bet it's possible to kill a saw in one tank of gas. It's only got to run too lean for a few minutes, overheat once, and the damage is done.

Like the guys mention, 2 stroke motorbikes have a more sophisticated carby, because they are expected to be able to cruise at 1/2 revs / 1/2 throttle all day.

It can likely be compensated for by using a bit more lube and re-tuning the carb so it's slightly rich. But I think how the saw is being operated is the main issue. The "treat it like a light switch" comment is good advice. If you try and hold a light switch 1/2 on, it will soon burn up too.

The problem may not occur with every model of saw, but that's more good luck than anything else.

The thing is, I've talked to several builders who use their saw at half throttle quite a bit. And from what I've heard you shouldn't run at full throttle while doing light work like brushing.

[barbender]

I have a couple of saws I used on a log building project. One burned down (Husky 346xp) due to a defective carb intake boot. There was a factory bulletin on it, and I brought it in several times and told him it acted like it had an air leak. It had a bog and wouldn't respond to the screws. The mechanic would take it and tune it for me🙄 It finally burned down, and they immediately asked, "aren't you log building?". I was about ready to choke the guy. He rebuilt it, I said "what about the air leak that caused this?". His answer was, "yeah, sometimes just taking them apart and putting them back together will fix that". I am not kidding. Obviously I don't buy anything there anymore. Anyways, I finally found the carb boot on my own, went to a different dealer and they said, "yeah there's a service bulletin and an updated part for that."🤦‍♂️ My point in all of this is, the dealer will often try to blame it on you when it is a defective saw. Mine melting had nothing to do with how I was using it. 

  If you're blipping the throttle vs just holding it at a certain rpm with low load, I don't see a problem. I could see the smart carb 261 maybe having an issue overcompensating, but log builders have been doing it that way for a long time and I think they expect better service life than one tank. At the very least I'd run 32:1 or so for oil. Good luck, I hope you get it figured.

[JaredR]

I have a couple of saws I used on a log building project. One burned down (Husky 346xp) due to a defective carb intake boot. There was a factory bulletin on it, and I brought it in several times and told him it acted like it had an air leak. It had a bog and wouldn't respond to the screws. The mechanic would take it and tune it for me🙄 It finally burned down, and they immediately asked, "aren't you log building?". I was about ready to choke the guy. He rebuilt it, I said "what about the air leak that caused this?". His answer was, "yeah, sometimes just taking them apart and putting them back together will fix that". I am not kidding. Obviously I don't buy anything there anymore. Anyways, I finally found the carb boot on my own, went to a different dealer and they said, "yeah there's a service bulletin and an updated part for that."🤦‍♂️ My point in all of this is, the dealer will often try to blame it on you when it is a defective saw. Mine melting had nothing to do with how I was using it.

 If you're blipping the throttle vs just holding it at a certain rpm with low load, I don't see a problem. I could see the smart carb 261 maybe having an issue overcompensating, but log builders have been doing it that way for a long time and I think they expect better service life than one tank. At the very least I'd run 32:1 or so for oil. Good luck, I hope you get it figured.

Thanks for the info on this. Fortunately this dealer seems to be willing to work with us, as he is kinda scratching his head as well.
I'm going to wait until I hear back on what he finds out when he tears it apart and I'll post it up here. I just had no idea that saws are so finicky and in my experience poorly designed.

[barbender]

They're usually not that finicky, in my experience. Something is amiss.

[btulloh]

I hope things work out on the saw.  This is all pretty surprising and new to me.  I get the full-throttle thing for normal use in felling or bucking or even trimming limbs, but doing the kind of work you're talking about is not a full-throttle or idle situation, and there are lot's of people doing joinery or carving.  Stihl makes carving bars and seems to know that market, and they are pretty good in general.  Seems like there would be some recommendations or guidance from the factory (like designers or engineers with actual knowledge) about these less than WOT uses.  Mixture, tuning, or something.  This just doesn't sound like it should be a problem when the saw is running almost unloaded.

(Did @HolmenTree check in on this topic?  He knows some stuff!)

Looking forward to your happy resolution and some real answers about using the saws like this.

[lxskllr]

Yea, this thread's kinda blown my mind. I thought I had the saw thing figured out, and now a bunch of people are saying "Yea, doing x isn't good...". I'd love to hear from an engineer on it.

[JaredR]

Yea, this thread's kinda blown my mind. I thought I had the saw thing figured out, and now a bunch of people are saying "Yea, doing x isn't good...". I'd love to hear from an engineer on it.

Yeah, same here. I've used saws for cutting firewood and some misc stuff, but this is the first time I'm seriously using them. I really enjoy learning new stuff but this one has been kind of baffling and I think a lot of the advice I've been getting is from people who don't really know their stuff.

I hope things work out on the saw.  This is all pretty surprising and new to me.  I get the full-throttle thing for normal use in felling or bucking or even trimming limbs, but doing the kind of work you're talking about is not a full-throttle or idle situation, and there are lot's of people doing joinery or carving.  Stihl makes carving bars and seems to know that market, and they are pretty good in general.  Seems like there would be some recommendations or guidance from the factory (like designers or engineers with actual knowledge) about these less than WOT uses.  Mixture, tuning, or something.  This just doesn't sound like it should be a problem when the saw is running almost unloaded.

(Did @HolmenTree check in on this topic?  He knows some stuff!)

Looking forward to your happy resolution and some real answers about using the saws like this.

Thanks, me too! That's actually the main reason I'm getting ticked off is the seeming negligence on Stihl's side. If their saws are this finicky at least their dealers should be aware of it and warn people.

Thanks for calling someone else in, I'm really wanting to hear from someone knowledgeable. 

[btulloh]

Just poking around looking for any factory info.  Found two pertinent references - one on m-tronic web page, one video about m-tronic.

Web info says "adjusts to all external conditions".  Video says m-tronic adjusts fuel/air mix to any rpm's.  Keep in mind, these are both SALES related, not engineering.  Sometimes the sales end of things can embellish to suit THEIR needs though companies like Stihl and Husky can't really afford to have a big mis-match between sales claims and actual performance.  Too much at stake.

[btulloh]

I'm really wanting to hear from someone knowledgeable

Just to keep from rustling any feathers, a lot of the people who've responded are knowledgeable and experienced.  None of us knows everything about some of this new tech and we're all doing our best keep up with it.  Most experience is going to be with standard carbs and screw-driver tuning, cause that's what's been around a long time.

My personal experience with M-tronic is that it works fine for anything I've done and I've never really thought about anything other than starting the saw and doing what I need to do.  I do follow their directions on cold-start and hot start, but that's about it.  (I've finally gotten old enough to realize that procedures in equipment manuals provide useful advice. :D)

[JaredR]

Just poking around looking for any factory info.  Found two pertinent references - one on m-tronic web page, one video about m-tronic.

Web info says "adjusts to all external conditions".  Video says m-tronic adjusts fuel/air mix to any rpm's.  Keep in mind, these are both SALES related, not engineering.  Sometimes the sales end of things can embellish to suit THEIR needs though companies like Stihl and Husky can't really afford to have a big mis-match between sales claims and actual performance.  Too much at stake.

So in my mind that's how a self-adjusting piece of a equipment should be designed to work, but I'm being told that they apparently can self-adjust to self-destruct. I thought the idea behind the M-Tronic "improvement" was to minimize the knowledge need to run a saw. Especially relating to adjusting the carb.

I'm really wanting to hear from someone knowledgeable

Just to keep from rustling any feathers, a lot of the people who've responded are knowledgeable and experienced.  None of us knows everything about some of this new tech and we're all doing our best keep up with it.  Most experience is going to be with standard carbs and screw-driver tuning, cause that's what's been around a long time.

My personal experience with M-tronic is that it works fine for anything I've done and I've never really thought about anything other than starting the saw and doing what I need to do.  I do follow their directions on cold-start and hot start, but that's about it.  (I've finally gotten old enough to realize that procedures in equipment manuals provide useful advice. :D)

That comment was in regard to the conflicting advice I've heard from multiple sources, not all on this site. Supposedly saws should be ran WOT, but they also shouldn't, they should always be fully loaded or they will not last, but log home-builders use them like this regularly. It's like a can of worms and I expected better advice considering saws have been around for a long time.  ???

I understand the newness to M-Tronic, but please bear in mind that the second saw to do this was a regular carbed model.

[barbender]

Chainsaws seem to bring out some of the same people that can't behave when religion and politics come up for some reason. They usually don't last long here because this site is tightly moderated but for instance, take a subject like oil mix ratio. Some will be on the run it rich side, others will be proponents of 100:1 or your fuel/air ratio will be too lean and burn up your saw (and you may even suffer eternal punishment)😂 So there's a lot to sort through. I'd say stick with the advice of those doing similar work with the same saws, see if you're doing something different. Check your gas/oil mix again. It is very suspect being you had TWO saws melt down immediately.

[btulloh]

That comment was in regard to the conflicting advice I've heard from multiple sources, not all on this site

I understood your original comment.  Just trying to head off any potential misunderstanding.  

This is a useful discussion, and hopefully it will lead to a definitive answer.

[JaredR]

Chainsaws seem to bring out some of the same people that can't behave when religion and politics come up for some reason. They usually don't last long here because this site is tightly moderated but for instance, take a subject like oil mix ratio. Some will be on the run it rich side, others will be proponents of 100:1 or your fuel/air ratio will be too lean and burn up your saw (and you may even suffer eternal punishment)😂 So there's a lot to sort through. I'd say stick with the advice of those doing similar work with the same saws, see if you're doing something different. Check your gas/oil mix again. It is very suspect being you had TWO saws melt down immediately.

Oh, I think that's any subject.  :D I was hoping some log builders would weigh in, and I appreciate your advice. I think these saws are defective. 
I have checked my mix, believe me. :D And as I've told others, our 661 C-M is running the same exact gas from the same containers, has about twice as much time on it as the two 261s, and has had no issues.

[JaredR]

That comment was in regard to the conflicting advice I've heard from multiple sources, not all on this site

I understood your original comment.  Just trying to head off any potential misunderstanding.  

This is a useful discussion, and hopefully it will lead to a definitive answer.

I understand, thanks!
Same here. I'm hoping between you guys and some others sources I'm tapping into we can figure it out. I don't want to mess up another saw, and being a small business taking on a new line of work cash is tight without all of this. I just want to find out what the problem is as I know people use these saws to do this work and have for years. Shoot, if we had not been mixing our fuel I would be happy as I would at least know what was wrong.

[mike_belben]

Cmon @barbender ive been behaving this time.   Now if you dont know 100:1 is proven to save 1.3 polar bears per day youre an idiot!

[mike_belben]

To the OP,  have you got an infrared temp gun?

Pistons transfering to jugs is entirely a temp thing and you should get in tune with that concept asap before cooking another.  Richen your mix, richen your screws, increase your cool down breaks by idling it flat on the floor periodically.  And beware the clutch bearing needs manual lubrication now and then.  It is engaged any time the chain isnt.