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40:1 in an MS261C-M??

Gypo Logger

Gypo Logger

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I run mine at 10:1!!!

Just to be sure!!!
That’s a smokin’ good idea!
I think 50:1 is not just an epa thing, it’s a fool proof ratio designed to cover almost every cutting application. Why would any dealer suggest anything more than 50:1 to half throttle home owners?
 
pioneerguy600

pioneerguy600

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I run mine at 10:1!!!

Just to be sure!!!
I have one very old chainsaw that called for 8:1 from the manufacturer, best skeeter repellent machine ever. Modern saws running modern 2 stroke oil will do well on 50:1 but all my modified saws drink 40:1 with no issues, they all turn several thousand RPM over factory posted limits, they are not your average homeowner saws.
 
Gypo Logger

Gypo Logger

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I have one very old chainsaw that called for 8:1 from the manufacturer, best skeeter repellent machine ever. Modern saws running modern 2 stroke oil will do well on 50:1 but all my modified saws drink 40:1 with no issues, they all turn several thousand RPM over factory posted limits, they are not your average homeowner saws.
I wonder how long your 8:1 would stay idling and how big the cloud of smoke would be when you finally goosed it?
Would bring a whole new dimension to vaping I would guess.
 
Tom B.

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Running a thicker mix will destroy the engine? A leaner mix certainly will, but thicker?! Nah. Just carbon issues perhaps if it isn't run WOT and heated up well.
Todays oils are better refined, burn cleaner and may have detergents. All that helps alleviate carbon build-up, fouling.
Try a tank of 40:1 and see how it runs. You might have to do some carb tuning but see how it runs. I highly doubt it would "destroy the engine".
 
pioneerguy600

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I wonder how long your 8:1 would stay idling and how big the cloud of smoke would be when you finally goosed it?
Would bring a whole new dimension to vaping I would guess.
It will idle at 1000 rpm all day at that mix but back when it was made they were running 30 WT crankcase oil, it didn`t burn well so the instructions was to clean out the exhaust ports and muffler every 40 hours of run time. The air would have been blue at 5,000 WOT.
 
BlacknTan

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The more fuel and oil threads I read, the more my head feels like it is going to explode!

My current juice is VP 94 octane ethanol free fuel mixed @45:1 with Husky XP+. When I burn up the VP, my next fuel will be this...

https://www.sunocoracefuels.com/fuel/optima

mixed @ 45:1 with XP+..

There is a NASCAR Modified track close by, so the Sunoco is readily available at a decent price.

PS,

I can't bring myself to run 50:1, so I feel I'm safe, and my mixes are always very accurate.
 
pioneerguy600

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Oil threads, PFFFFFFFFT, just gives everyone a chance to post what they run, as far as oil goes, some oil in the gas is better than no oil in the gas. I have ran 30 wt in the early years at any ratio on through to now using any two stroke oil made and never lost a saw, from 1958 til present. Those that post about only using specific oils made for certain engines are not posting from experience, just posting from what they read on manuals and sites. Flame away....LOL
 
MacAttack

MacAttack

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Oil threads, PFFFFFFFFT, just gives everyone a chance to post what they run, as far as oil goes, some oil in the gas is better than no oil in the gas. I have ran 30 wt in the early years at any ratio on through to now using any two stroke oil made and never lost a saw, from 1958 til present. Those that post about only using specific oils made for certain engines are not posting from experience, just posting from what they read on manuals and sites. Flame away....LOL
I ran my saw for YEARS on Pennzoil Snowmobile oil mixed at whatever I was running in my 2 stroke ATV. Never missed a beat and years later has great compression and no issues.
 
MaddBomber

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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). Stihl won't honor any warranty work if it's discovered that it's been run on anything other than 50:1..... So I've been told by a tech. Pretty sure there's more going on than just EPA regs.

you best not run the silver bottle Stihl at 40 to one, the orange is fine at 40 to 1
Learned that the hard way. Stihl HP Ultra is excellent at 50:1, and can even rid your combustion chamber of carbon. However at 40:1, it's creates gummy carbon like crazy. I cracked a piston due to carbon buildup on an MS260 at around 200 tanks of 40:1 HP Ultra.
 
Andyshine77

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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). Stihl won't honor any warranty work if it's discovered that it's been run on anything other than 50:1..... So I've been told by a tech. Pretty sure there's more going on than just EPA regs.


Learned that the hard way. Stihl HP Ultra is excellent at 50:1, and can even rid your combustion chamber of carbon. However at 40:1, it's creates gummy carbon like crazy. I cracked a piston due to carbon buildup on an MS260 at around 200 tanks of 40:1 HP Ultra.
How will they know you ran 40:1? Dealers now carry expensive lab equipment? I had an early 5100 they let go on it's first tank. Dealer sent the saw back to Dolmar for inspection, they said the saw didn't have enough oil in the fuel, I run 32:1 The saw had a leaking intake boot, trying to weasel their way out of warranty is all, that's the name of the game.

Ultra runs dirty as hell at any ratio.

Cracked a piston do to carbon buildup? Highly unlikely.

Fact is if the system for some reason can't adjust for variation in fuel, the system would be defective, as it's impossible to get a perfect ratio each time. All the the solenoid does is regulate fuel flow, if the saw starts to run lean it lets in more fuel, rich less fuel. Sorry your information and reasoning is not sound.
 
MaddBomber

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How will they know you ran 40:1? Dealers now carry expensive lab equipment? I had an early 5100 they let go on it's first tank. Dealer sent the saw back to Dolmar for inspection, they said the saw didn't have enough oil in the fuel, I run 32:1
The saw had a leaking intake boot, trying to weasel their way out of warranty is all, that's the name of the game.

Ultra runs dirty as hell at any ratio.

Cracked a piston do to carbon buildup? Highly unlikely.

Fact is if the system for some reason can't adjust for variation in fuel, the system would be defective, as it's impossible to get a perfect ratio each time. All the the solenoid does is regulate fuel flow, if the saw starts to run lean it lets in more fuel, rich less fuel. Sorry your information and reasoning is not sound.
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.
 
MaddBomber

MaddBomber

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As an edit: I prefer 40:1, but have switched to 50:1 due to input and information learned on this site. I don't think there's enough of a difference between the two mix ratios to cause any issues other than carbon. I'm no Stihl oil advocate by any means. I'm simply saying that if you bought a 6 pack of it to extend a warranty, it's okay to use. However, over extended (200 tanks) use, you'll eventually run into carbon issues unless mixed at the recommended ratio.
 
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