Mtronic and fuel mixtures.

[Boogedy_Man]

I'm confused on something...

Everyone recommends a little more oil for milling....so if I were to run a 661C at 40:1 or 32:1, would the saw automatically adjust the air fuel ratio for the difference, or would I be running lean all the time? I run Stihl full synthetic in everything.

I tend to think I'll be fine at 50:1, but I really don't know. I have a Husky weedeater that I've ran boat oil in for years, and a Poulan saw that I have managed to run on gas and a splash of bar oil when I realized deep in the woods I had a container of straight gas. I fully expected to cook the Poulan, but it made it through the whole smokey tank of fuel without issue. Both escaped any hint of scoring, so I often wonder if it's a matter of much to do about nothing.

 

[Rockjock]

I'm confused on something...

Everyone recommends a little more oil for milling....so if I were to run a 661C at 40:1 or 32:1, would the saw automatically adjust the air fuel ratio for the difference, or would I be running lean all the time? I run Stihl full synthetic in everything.

I tend to think I'll be fine at 50:1, but I really don't know. I have a Husky weedeater that I've ran boat oil in for years, and a Poulan saw that I have managed to run on gas and a splash of bar oil when I realized deep in the woods I had a container of straight gas. I fully expected to cook the Poulan, but it made it through the whole smokey tank of fuel without issue. Both escaped any hint of scoring, so I often wonder if it's a matter of much to do about nothing.

I have seen quite a few milling saws that have run 50:1 with no ill effects. I think the biggest issue is when there is not enough load on the saw and it just overheats and burns up. I have also seen chainsaws using the incorrect or incorrect type of oil and they seem to have more carbon buildup from what I have seen. OP you have to remember that back in the day it was a motor oil that was mixed with the fuel to make the mix. The lubricants are much better presently so many just simplify things by running 50:1. Seem many an old mac come in and just needing a tune up. Customer cuts a great deal of hardwood and runs e free 50:1.

 

[CR888]

Yes the Mtronic will adjust to different oil ratio fuel mixes.

 

[Rockjock]

Yes the Mtronic will adjust to different oil ratio fuel mixes.

Actually it does not. It can only adjust to air/fuel ratio. Unless the " brain " can analyze the fuel, determine that it is mixed at what ratio and adjust from there.

 

[Boogedy_Man]

I ran all my old 60's Rotax sleds on whatever oil I could find in my grandpa's barn, mixed with whatever I could siphon out of my Dad's truck.

 

[1Alpha1]

Too bad the Mtronic can't tell when it's being straight-gassed, before any harm is done. For some, that would be a great feature.

It can't tell straight-gassing from a 20:1 mix.

 

[blsnelling]

Yes, the 661 will re-tune itself, regardless of the oil or ratio used.

 

[Boogedy_Man]

Ok, I've got 6 to 1 and half dozen to the other, lol.

My 461 isn't mtronic...how much risk am I taking running it at 40:1?

 

[blsnelling]

Risk? How would there be risk? I run 32:1 in all of my saws. Many people here do.

 

[Boogedy_Man]

Because I've not touched the carb....so, my understanding is the A/F ratio would be lean with increased oil.

I think it's probably by a tiny amount, but people often caution about it.

 

[blsnelling]

You may or may not need to tweak your tune. Even the weather affects your tune.

 

[Boogedy_Man]

So now worries in the 661, may need to richen the 461. I can deal with that.

I tuned my little poulan over the winter (erring on the rich side), and it's running pig rich lately. Of course, it's been up to 80 here. I get the difference in the weather. I don't want to retune anything throughout the year....just find a happy medium

 

[1Alpha1]

Because I've not touched the carb....so, my understanding is the A/F ratio would be lean with increased oil.

My 461 isn't mtronic...how much risk am I taking running it at 40:1?

You are fine (and quite safe) @ 40:1 mix ratio.

 

[1Alpha1]

https://www.stihlusa.com/products/technology/stihl-m-tronic/

 

[Big_Wood]

Actually it does not. It can only adjust to air/fuel ratio. Unless the " brain " can analyze the fuel, determine that it is mixed at what ratio and adjust from there.

it adjust the air/fuel ratio yes, how much oil is in the fuel half is unknown to mtronic but it doesn't care. the amount of fuel is what it controls, how much oil in that fuel is irrelevant to mtronic. if oil displaces fuel with a heavier mix mtronic just dumps more fuel in to compensate. it's not like switching mix ratio's in a manual adjust carb where the oil displacing fuel could make the saw run lean but it seems you are thinking like they are the same? so yes it does, aren't you a dealer? lol

 

[Rockjock]

it adjust the air/fuel ratio yes, how much oil is in the fuel half is unknown to mtronic but it doesn't care. the amount of fuel is what it controls, how much oil in that fuel is irrelevant to mtronic. if oil displaces fuel with a heavier mix mtronic just dumps more fuel in to compensate. it's not like switching mix ratio's in a manual adjust carb where the oil displacing fuel could make the saw run lean but it seems you are thinking like they are the same? so yes it does, aren't you a dealer? lol

As I said it can not detect how much oil is in the fuel. It assumes you are using the recommended amount of oil ( 50:1 ) There is no analyzer built into the fuel filter that communicates to the CPU. LOL
Yes I am a dealer. I am also a self professed chainsaw addict.

 

[Little Al]

Because I've not touched the carb....so, my understanding is the A/F ratio would be lean with increased oil.

I think it's probably by a tiny amount, but people often caution about it.

Changes in altitude & barometric pressure would likely affect the tune more than a change from say 50 to 32/1 or the other way around. I'm also a 32/1 mixer,but each to his own.

 

[blsnelling]

MTronic doesn't need to know how much fuel is in the mix. It will tune accordingly regardless of 50:1 or 32:1, just like it adjusts for any other variable that affects tune.

 

[Boogedy_Man]

Well, I just mixed up some 40:1 and I'll just roll with it

If the little motors grenade I'll post some fun pics!

 

[Big_Wood]

As I said it can not detect how much oil is in the fuel. It assumes you are using the recommended amount of oil ( 50:1 ) There is no analyzer built into the fuel filter that communicates to the CPU. LOL
Yes I am a dealer. I am also a self professed chainsaw addict.

It doesn't assume anything, it just simply doesn't know and doesn't care. It controls tune with fuel. You could run straight gas in there and it would still tune perfectly lol your exact words were no it doesn't tune for different mixes and I'm telling you it does. Don't try turn this to a you meant this discussion cause I know what you meant the first time. It's to late to make a save rockjock. Carry on. everyone makes mistakes, even dealers lol.