Interesting find troubleshooting MS261 C-M hard start issue

[vdavidoff]

It seems like the brand specific subforum isn't the right place for this, so I'm posting it here, though I'm kinda confused how to use the brand specific subforum, even after reading the thread about how to use it.

Anyway, I have been troubleshooting an issue with my MS261 C-m where it runs fine from a cold start, but as soon as I set it down and it idles for a minute or two, or I shut it off for even just a few minutes, getting it started again is a nightmare. I will spare you the details because I have searched the forums and I know this is common problem, though I have yet to find anyone reporting a fix.

I've cleaned, inspected, and replaced a bunch of parts, and I am awaiting receipt of the newer/redesigned solenoid and hoping that fixes things. On that note, today I had an idea of something to try and the results seem interesting, so I figured I'd share them.

I decided that the problem might be that the solenoid is getting hot and malfunctioning, so when it started misbehaving I sprayed the solenoid with contact cleaner - not to clean it, but just because it would cool the solenoid and seemed generally safe to be spraying on it. I just stopped the saw, popped over the cover, sprayed onto the solenoid for 1-2 seconds, then put the cover back on.

I did this several times today as the saw started to misbehave, and it seemed to mitigate. I couldn't get the saw to re-start without holding the throttle full open while pulling the starter (I realize this dangerous and also just a bad idea), but after spraying the solenoid, it would fire right up like that and run fine for 10-15m until I had to do it again.

It's possible that what was really going on there was some residual vapor from the contact cleaner was sort of acting like starting fluid, but it wasn't like it fired up well then died - it fired up and ran like there was never a problem. I guess it's still possible that a "starter fluid" effect and starting it full throttle could have coaxed m-tronic into doing something "right", I really don't know. Maybe it was something else entirely, but this is the only thing I have found so far that worked every time, and doesn't just seem like it was some sort of coincidence.

Anyway, just figured I'd share this in case anyone else is fighting with this and maybe this is useful information. In my case it seems like (though I am not certain) what happens is the saw runs really lean at idle in the "start" position, then super rich (to the point of dying) as son as you touch the throttle and it flips to "run", when things are acting up. Additionally sometimes on throttle before it dies it seems like m-tronic is adjusting fuel in major ways, but can't get it right, then it dies. I can be holding the throttle in a constant position and it'll spin up, then wind down, then die, all with the same position of the throttle. Oh, also, when this happens the saw will run fine in any position running in the "start" position, but in the "run" position, if the saw is upright or tilted to the side with the starter it will die. In other words it runs if it's tilted towards the side where the bar is attached, but dies (or really, really wants to if I'm not careful) once it's tipped upright or over to the opposite side from the bar.. My first though there was something in the fuel line, carb, etc, but that doesn't seem to be the case...I think the tilting is just exacerbating whatever is wrong with the solenoid.

Like I say, I am hoping the new solenoid fixes it, but we'll see.

Andy

 

[Ketchup]

Are you running the fine micron fuel filter?

 

[drf256]

Did you vac and pressure test the saw? You should.

When troubleshooting M-tronic problems I learned that hard way that one should do the basic trouble shooting first before blaming the MT components. It’s rarely the MT that’s the cause.

Replacing, I am assuming, black solenoid with the new white one is a good idea anyway. I hope you got the kit with the orange fuel filter in it.

The default on the solenoid is wide open/flooding. The computer leans the saw out.

A perfectly functioning system can malfunction is the saw gets too hot. It can’t get rich enough at WOT by default, so the computer starts to not lean out the solenoid at other times when it would be leaned out. Then you just flood away.

You can also have problems if you are running winter fuel in the saw when it’s hot out. Vapor lock more common as the cheaper winter fuel has more cheap Hexane in it which gasses out in the extreme heat.

Try a different fuel and oil mix and see if it makes any difference. It did for me on a few ported 261. Motul800 at 30:1 worked great in all of my saws except for the 261CM. It was too thick/viscous to flow correctly and did just what I wrote above. Switched mix and all was well. I actually punch the main nozzle out of my carbs when I build them and drill the jet. The factory enlarge the jet on most white solenoid saws but not all of them. The black solenoid saws seem to all have the smaller jetting and they need to be drilled.

 

[vdavidoff]

If the orange filter is the fine micron one (I believe it is), then yeah, that's what I've got installed, and that's actually what the saw came with brand new.

I haven't pressure tested the fuel system but I do have a tester. I was going to do it at the same time I was replacing the tank vent but, I just didn't. You are right though, I should do that.

The saw only sees action in the spring, summer and fall. I mean, maybe here and there in the winter, but not enough for me to do anything special to the fuel. I just run 91 octane (same I put in my truck). It's not ethanol free, but that's what I've got. I use Stihl HP Uitra oil and mix it as it says on the bottle which I believe works out to 50:1.

I'm gonna swap the solenoid out, probably pressure test at the same time since I'll have the saw apart anyway, then see how things go, before getting into carb mods, but I will keep that in mind.

Thanks for the replies.

 

[drf256]

Don’t think you’ll need the carb mods, really only needed on ported saws that use longer bars in longer cuts.

The fuel does matter. Try grabbing a fresh gallon now while it’s summer fuel. I know it sounds dumb, but you have little to lose trying. I wouldn’t have believed it myself till I read it here and had it happen. You’ll be fine with your Stihl ultra at 50:1, though many here don’t like that oil or ratio (I’m one of them). But it shouldn’t cause a run issue.

I’m surprised you have an orange filter and black solenoid. I’ve only seen the newer trouble free white one on saws with the orange filter from the factory.

I’m referring to pressure and vacuum testing the saw itself, not just the fuel system. Yes, pressure testing the carb to see if it holds pressure is a good idea. But also, vac and pressure test the entire saw and well. Block off the exhaust, plug the decomp, and either get the Stihl adapter to cover the boot face or tape it shut and test through the impulse line.

I’ve seen the MT system compensate for all sorts of odd issues. The system will actually compensate for massive vacuum leaks and just act a bit oddly. It’s just a whole ‘Notha learning curve. Like everything else, check the piston through the exhaust port and do everything you’d ordinarily do an a non computer saw first. That’s really all I was eluding to.

 

[Mastermind]

When the weather gets hot, I always get calls about saws not acting right. I recommend a dose of canned fuel to rule out a case of improper gasoline. After that, I usually never hear from the user again. Next is a solenoid swap. Use the newest white solenoid, and be sure to use the correct reset procedure. If your 261 has a white solenoid from the factory, great.....just swap and reset. If not, I'd recommend a coil swap as well. Using the newest coil, solenoid, and filter allows you to reset with the M3 process.

 

[vdavidoff]

I might switch back to canned fuel to see if I notice a difference, but man, that stuff is just so freakin' expensive. I will look into replacing the coil, too. I had done that before but was finding conflicting information regarding if you could really take the newer coil and have it work right in an older 261.

 

[Ketchup]

Man, I hate heat issues.

Winterized fuel can really make your saws suck when the temperature spikes. A slightly cheaper option to canned gas is getting fuel at your local airport. They should have several non-ethanol options that are stable across a wide temperature range and are half the price of canned gas.

Just a thought and not the root of your problem, but it’s possible that you damaged your solenoid by rapid cooling it.

I think gas or solenoid will fix your issue. I would hold off on a new coil until you try the first two.

 

[vdavidoff]

I didn't even think about the fact that the fuel may be winterized from the pump. Never really had to think about it I guess.

I also forgot to mention that I use Stabil in my fuel. Hopefully I'm not punching myself in the face here...

 

[drf256]

Did you try canned fuel yet?

 

[Fullkip]

Put a new wiring harness in it if it's not fuel related. I did that on my Ms 362 problem solved. You no the small wiring that connects the coil to solenoid and switch. Rich the chainsaw guy told me about it.

 

[vdavidoff]

Nearest Stihl dealer / place to get canned fuel is out. Gonna go a bit further to try to get some tomorrow, probably. Of course, the saw ran pretty well today. After refueling I still had to be careful when I started it, had to sort of ease it back into running (couldn't just slam the gas or it'd die), but once I got it running, which was relatively quick, it worked fine. It was considerably cooler today than it has been, but I have no idea if that was actually a factor.

 

[Steve Taylor]

I have been having the same problem with mine since it was new. Cold weather it starts great but let it get over 75 and you're pulling your arm off.
I will be watching for advice too

 

[Mastermind]

I have been having the same problem with mine since it was new. Cold weather it starts great but let it get over 75 and you're pulling your arm off.
I will be watching for advice too

Sounds like it needs a solenoid.

 

[Steve Taylor]

It might, the local dealer said he would check it out for me but I haven't quit long enough yet for him to do it.

 

[Mastermind]

It might, the local dealer said he would check it out for me but I haven't quit long enough yet for him to do it.

It needs more fuel in cool weather. So if it becomes hard to start in hot weather, its probably too rich, which is a sign of a leaky solenoid.

 

[vdavidoff]

I have been having the same problem with mine since it was new. Cold weather it starts great but let it get over 75 and you're pulling your arm off.
I will be watching for advice too

Interesting you should mention 75. Hardly scientific, I know, but that seems to be about the cutoff for me too, based on recent experience (though I don't clearly remember the details from last season). I am also at 9500' which I know doesn't help, but that's a big part of why I went with a saw that was supposed to autotune.

 

[Mastermind]

Interesting you should mention 75. Hardly scientific, I know, but that seems to be about the cutoff for me too, based on recent experience (though I don't clearly remember the details from last season). I am also at 9500' which I know doesn't help, but that's a big part of why I went with a saw that was supposed to autotune.

At 9500' I'd imagine the M-Tronic system have a devil of a time running lean enough.

 

[vdavidoff]

Well, I was able to pick up some canned fuel (not Stihl brand, TruFuel), but the weather for the next week or so may make it hard to get out there. We'll see. I will report back when I either have some runtime on the saw with the canned fuel, or the new solenoid installed (it shipped a few days ago), or both.

 

[MustangMike]

Another possible problem with M Tronic saws ... if you try to run them with very low fuel in the tank, the computer compensates for the "lean" mixture (it is designed to to that so an air leak does not burn it up).

They will cause the computer to go rich, and for about 6 tanks it will be hard to start unless you hold the throttle open (they don't have fast idle).

Also, I presume, you start it on Run when warm, not on Start! Start is only for Cold Starts.