MS261CM M-Tronic Issues and Many GFY’s

[drf256]

Makes sense.

I think it’s heat.

Too much advance, too much compression, not enough fuel to overcome the issue, or it floods trying to.

Gonna pull jug first, adjust squish to 20. Vac test. If that fails, back to the timing, then the carb.

I’d rather get 20 as squish anyway.

 

[Redbull661]

I know it'll sound weird. But I had similar issues when I tested small MT saws (261 362) with different oil ratios with heavy thick oil (like motul).

Back your ratio up to 40:1. If it works then it's an easy fix. If it doesn't you can just add the 40:1 gas to your 32:1 mix and no harm, and continue trouble shooting.

 

[Stump Shot]

 

[redlight066]

Al, that's a tough one. I would check the fuel filter and make sure its free of restriction. Blow through it. I don't think it's the mods that are giving you this headache. I've never had a problem with the auto-tune/M-tronic carbs keeping up with the porting and mods. They may cough, snort and act a little confused on the first cut, but always compensate and are dialed in by the end of the second cut. I'm very interested if what Julian said cures it.

 

[hseII]

I know it'll sound weird. But I had similar issues when I tested small MT saws (261 362) with different oil ratios with heavy thick oil (like motul).

Back your ratio up to 40:1. If it works then it's an easy fix. If it doesn't you can just add the 40:1 gas to your 32:1 mix and no harm, and continue trouble shooting.

That does sound different: I’m not saying that’s incorrect, just different.

32:1 Red Armor was the 1st few tanks.


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[Redbull661]

I may be totally wrong, but it's very easy to do and worth exploring, based on my previous results. Although that was with H1R. Still, motul has a similar thick viscosity and high temp burn...so it's possible. Again easy to do and worth a shot.

 

[hseII]

I may be totally wrong, but it's very easy to do and worth exploring, based on my previous results. Although that was with H1R. Still, motul has a similar thick viscosity and high temp burn...so it's possible. Again easy to do and worth a shot.

Oh I Agree on being easy to prove & worth exploring.

Is motul thicker or thinner than RA?


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[Mastermind]

The northerners got weird gas. Winter blend, summer blend, *f-wordeduperthanasoupsandwich blend.

I'm with Redbull.....

It's fuel, or oil related.

 

[drf256]

A few things since speaking to guys this am.

I did the 90 sec reset, but never did any 60 seconds after. The Stihl bulletin I saw didnt say that.

I didnt do first cuts with any realistic bar length, not sure if that matters.

My mix could be 28:1, I've always been "a little extra wont hurt" kinda guy. It's my break in fuel. It's also stored outside at 32*. It could have moisture, but its sealed.

I'm coming to the conclusion that a few things are happening:

The saw is building heat

The MT cant compensate

The reason it cant compensate COULD be the viscosity of the mix, the popoff pressure (but the engineers are smarter than me), or maybe the timing?

 

[huskyboy]

It could have moisture, but its sealed.

Have you put your gas in a clear glass jar to see if there’s water in it?

 

[Duane(Pa)]

Brother Randy has “40:1 only” stickers for MTrons. IDK?

 

[Duane(Pa)]

Pix of BFH

 

[dall]

my mtronics didnt like 32:1 either i run 40:1

 

[CR888]

Motul 800 @32:1 would not be a combo that will run well in a 261, I'd take it back to 50:1 or try another oil @50:1 to rule that out. Next I would do as you thought which is back off the timing advance to rule that out. A 1/4" at the flywheel cutout is a fair bit and could potentially be too much giving symptoms you are seeing. I dile the timing in with incremental changes rather that applying X amount of advance. To much which can be a small fraction can really change running behaviour. You'll work it out doc, it'll be something basic is my guess.

 

[pro94lt]

50:1

 

[hseII]

my mtronics didnt like 32:1 either i run 40:1

That’s strange for me.

Both my 362 & this 261 didn’t seem to mind?


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[hseII]

Motul 800 @32:1 would not be a combo that will run well in a 261, I'd take it back to 50:1 or try another oil @50:1 to rule that out. Next I would do as you thought which is back off the timing advance to rule that out. A 1/4" at the flywheel cutout is a fair bit and could potentially be too much giving symptoms you are seeing. I dile the timing in with incremental changes rather that applying X amount of advance. To much which can be a small fraction can really change running behaviour. You'll work it out doc, it'll be something basic is my guess.

I’m not Running anything @ 50:1.




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[dall]

I’m not Running anything @ 50:1.




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50:1 is way too dry

 

[hseII]

The northerners got weird gas. Winter blend, summer blend, *f-wordeduperthanasoupsandwich blend.

I'm with Redbull.....

It's fuel, or oil related.

Very true.

This how the 4-62pulls got its name.


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[hseII]

50:1 is way too dry

I wholeheartedly agree.


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