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40:1 in an MS261C-M??

Andyshine77

Andyshine77

Tree Freak
Joined
Jan 25, 2004
Messages
10,789
Age
42
Location
Cincinnati, OH
A specialized hydrometer can easily check oil to fuel ratio. It literally takes minutes. A friend who raced a Honda CR125 professionally had one. Fairly inexpensive. But, yes, most dealers and techs don't have one. However, my 261 had a rattling noise and was sent to Virginia for a week before they sent it back. I'm sure they have the capability to test.
Carbon buildup had in fact cracked my piston. I set the squish to .019 in '09. In 2019, with the buildup the squish was .007! So yes, carbon cracked my piston. After I cleaned it the squish was .019.
Stihl oil is actually not bad at all. Hotsaws101 has a YouTube video all about mix oil and ratios. He's talked to manufacturers and specialists that helped him compare different qualities, viscosities, additives and select properties of multiple manufacturers. Stihl HP Ultra was hight on the quality list, and he even mentions the specifics of why it actually cleans carbon when mixed at 50:1.
In the post I linked, it is explained, by multiple people here, that oil molecules are larger than gasoline molecules, so more oil= less gas. Something that is easily tuned for by hand, but a system measuring volume cannot differentiate... Which is why you can still straight gas an MTronic.
It's also mentioned that oil doesn't cool anything, it is simply a lubricant. The gas actually has cooling properties (though barely significant). So if there's less cooling gasoline.... Yeah.... On a system that already has heat issues.
I wholeheartedly agree that manufacturers will weasel out of as much as they can.
Hotsaws 101 is full of it!! This has all been beaten to death a million times, all angles have been looked at and discussed, we all have a good understanding of what's what, you're not providing any unknown information. Oil does more than just lubricate! Ultra is bottom of the barrel, burns very dirty at any ratio, It lubes OK though. The fact you have carbon issues should answer the question, the answer is right in front of you. Who ever told you 40:1 will make less power is in the business of selling new saws, not making them last or make more power. Pretty much everyone here recommends 40:1 or 32:1 so I don't know what you mean buy learning to run 50:1 from this site.

If you start looking for an new car and want to know how good the engine is you ask an independent mechanic you trust, and do as much research as you can. What you're doing asking the salesman, you're listening to the salesmen, instead the mechanics and in some ceases engineers. They want you to believe they know all, when all they want is you to buy overpriced oil and a new tool as soon as possible. Some love Kool-Aid.
 
MaddBomber

MaddBomber

ArboristSite Operative
Joined
Mar 13, 2009
Messages
392
Location
NorthEast
Hotsaws 101 is full of it!! This has all been beaten to death a million times, all angles have been looked at and discussed, we all have a good understanding of what's what, you're not providing any unknown information. Oil does more than just lubricate! Ultra is bottom of the barrel, burns very dirty at any ratio, It lubes OK though. The fact you have carbon issues should answer the question, the answer is right in front of you. Who ever told you 40:1 will make less power is in the business of selling new saws, not making them last or make more power. Pretty much everyone here recommends 40:1 or 32:1 so I don't know what you mean buy learning to run 50:1 from this site.

If you start looking for an new car and want to know how good the engine is you ask an independent mechanic you trust, and do as much research as you can. What you're doing asking the salesman, you're listening to the salesmen, instead the mechanics and in some ceases engineers. They want you to believe they know all, when all they want is you to buy overpriced oil and a new tool as soon as possible. Some love Kool-Aid.
BwaHaaHaa!! You are hilarious!!
Wow.
Okay pal, you win.
You believe what you want.
I prefer to believe over 180 years of combined timber experience backed by math, repair costs, and a boat load of analytical data.
But yeah bro, you. You are right. Appearently you have to be.
And I just might add a bit of vodka to that Koolaid.
 
Andyshine77

Andyshine77

Tree Freak
Joined
Jan 25, 2004
Messages
10,789
Age
42
Location
Cincinnati, OH
BwaHaaHaa!! You are hilarious!!
Wow.
Okay pal, you win.
You believe what you want.
I prefer to believe over 180 years of combined timber experience backed by math, repair costs, and a boat load of analytical data.
But yeah bro, you. You are right. Appearently you have to be.
And I just might add a bit of vodka to that Koolaid.
OK Pal? no need to get touchy this is not personal to me. This has nothing to do with me, just the info that is already relatively well understood. Feel free to provide the data and change my mind. I'm always open to new ideas and information, however you have yet provided any, other than what some salesman told you. What does 180 years of combined timber experience have to do with understanding the physics involved in two cycle engines? The data from two cycle engine builder like Bell and Jennings among the builder from here and better yet the CART builders provide real information. I'm just calling it as I know it, you are free to disagree.
 
ericm979

ericm979

ArboristSite Operative
Joined
Apr 18, 2017
Messages
405
Location
Santa Cruz Mountains, California
FWIW, I had similar concerns a few months ago. I was told that 40:1 on an MTronic will produce less power and somehow cause it to run leaner (looking for the thread).
All premix two strokes run slightly leaner when the premix contains more oil. Until they're tuned or tune themselves.

It's because the carb meters liquid, in this case mixed oil and gas. Its jets and circuits are designed to flow a certain amount of liquid per unit of air. Oil is not fuel. If you put more oil in the premix, there's less gasoline. So your fuel:air ratio is leaner.

But the difference between 50:1 and 40:1 is small. It's unlikely to damage the engine unless it was running too lean already. M-tronic or Auto tune will compensate for the small difference. As to the power, it will probably be very slightly more, even after retuning manually or letting M-tronic do it. Studies show that everything else being equal, more oil makes slightly more power. Presumeably due to better ring sealing. But again the difference is so small you'll never notice it.

Saws are very mildly tuned industrial engines. They don't need lots of oil. It's just making smoke and burning $$$ for nothing. I run good synthetic oil at 50:1 in most of my saws. If I was milling or something extra stressful I'd run a little more oil and tune the carb to match (and go a little rich from there for extra cooling).
 
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