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What's the recommended fuel mix ratio determined by?

Robert P

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Jul 11, 2014
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I have a Remington Outlaw 46cc that calls for 40:1, an Echo CS352 34cc that calls for 50:1.

What's behind the different oil ratio recommendations?
 

Robert P

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I’d run 40:1 in both. More oil, more protection. Less oil, cleaner emissions. Good synthetic oils can be run at leaner ratios than lesser oils…oil is a black hole. Short version, run synthetic.
Doesn't more oil mean a leaner mix, less oil a richer mix?
 

Trains

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its such a small difference, you may need to adjust your jets, but your only talking a very small amount if at all, I find you adjust more for weather conditions than oil ratios.

personally I run 150mls in 5lts, or 32:1 mineral 2t castrol oil in all my equipment.
 

Bart

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Oil anecdotes. Had an 81 yz125 whose factory service manual called for 24:1 on Yamalube 2 and 16:1 on Yamalube R. Clearly different oils. Fast forward to the 90's and Optimol at 100:1 was the fad. One weekend I mixed up my gallons to cc math and ran 80 something to 1 and smoked out everyone behind me, so I was told. Clearly a different oil. Recently I've found Stihl synthetic a bit cleaner than regular oil. For a while everyone swore by 32:1. I'd say mix what the bottle says and make sure it's not TCW rated because water cooled two strokes aren't as cruel to oil as air cooled, I think rated TCA is for air cooled.

edit - small warning, too much oil seems intuitively safer, but carbon buildup could cause problems, possible ring sticking or bore scoring, so don't overdo it.
 
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Trains

Firewood Hack, wanna be tree climber
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If your having issues with carbon build up etc, look at your jetting, not your oil mixture (unless you dropped in 500mls in 5lts by mistake).
I have 30 year old saws that started their lives on 25:1, and when I went over them years later, they were clean inside, no carbon build up, no stuck rings, bit of splooge out the exhaust, but again, once new fuel lines, seals, carb kit and re tune, that cleared and burnt away.
Sure oils have changed, and improved, but I feel a lot of the reasons for leaner oil mix has to do with meeting epa, rather than leaving a protective oil coating in the engine, engines ive rebuilt on 50;1 are not in the same condition than those that I get where 32, or even 25:1 are still run, yeah some older chaps just keep doing what works for them, and wont change :). No fouled plugs or carbon build up in those saws either.
 

Bart

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Optimol appears to still be around. Back in the day the lore was that you could throw in some straight gas and finish your race without nuking your engine. Because of eutechting? Note I called it lore :) I used it briefly. Somewheres about then marketing speak made the new term ashless. Something to do with carbon buildup. Forgive the sparse memory. On the Yamaha oils the R was watery and I figured they put go juice in with the oil. The bike definitely ran better on it and smoked less.
 
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