2 Stroke Mix effect on Rich/Lean

[Jim 5]

I hope someone can confirm that I understand things correctly.

I understand that many newer 2 stroke engines are specifying 50:1 ratios, even in engines that used to spec 32:1. I was on the homelite website and my exact weedeater (that I bought 10 years ago)that specs 32:1 now specs 50:1 according to the website. I understand this is happening generally due to emissions reduction efforts.

My new Stihl chainsaw and leaf blower also spec 50:1. I would like a little additional protection and would like to run around 40:1 in all my equipment. I don't care if I lose a little protection in the homelite weedeater, because I'm looking for an excuse to replace that one....hate the curved shaft.

Anyhow, my house is about 3900' above sea-level and it is my understanding that as 2 stroke oil is increased in the fuel/oil mix, the carburation on the equipment experiences a slightly leaner condition. Can anyone confirm this is correct?

If I'm right about that, my thought is that my Stihl equipment could stand to be run a little more lean (by going to a 40:1 mix from a 50:1 mix) given how high my location is above sea level. If experience is any guide, the equipment runs nicely on a 40:1 mix.

Could anyone tell me whether I'm on the right track here, and if I'm harming the equipment in any way by going 40:1 instead of 50:1? I just don't know that much about 2 stroke engines/carburation/theory.

Thanks in advance for your thoughts!

 

[JTK]

If it runs well on 40:1, doesn't smoke you out or foul the plug, keep it on the oilier side. A higher dollar 2 cycle oil helps keep things cleaner as well. Lighter on the oil gives you snappier throttle response but shorter engine life.

Joel

 

[bonnie john]

WELL, that goes against all my experience using opti 2 at 100:1 and never having an engine failure or any premature wear
eg cheap mc culloch line trimmer, pulled the engine to bits at 15 years after the rest of it fell to bits, bore and piston looked like new chrome, bearings tight and no deposits in ports

Quote:

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If it runs well on 40:1, doesn't smoke you out or foul the plug, keep it on the oilier side. A higher dollar 2 cycle oil helps keep things cleaner as well. Lighter on the oil gives you snappier throttle response but shorter engine life.

Joel

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[flatlandtacoma]

Quote:

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my understanding that as 2 stroke oil is increased in the fuel/oil mix, the carburation on the equipment experiences a slightly leaner condition. Can anyone confirm this is correct?

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Correct. If you keep the needles set the same and add more oil, fuel goes down and air stays the same.

 

[Jim 5]

Thanks flatlandtaco...

Then at my altitude, it couldn't hurt things (from a carburation perspective) to add slightly more oil to mix for the 50:1 equipment.

 

[JHZR2]

is that really the case though???? oil is also a hydrocarbon.

If we assume gasoline as on average C7, and the oil is, say C35, you do have 5x more carbon per unit of air... however, it is not like it is replaced by an unburnable species.

Is this really a big problem? Id never heard of it.

Thanks,

JMH

 

[JTK]

Quote:

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... pulled the engine to bits at 15 years after the rest of it fell to bits, bore and piston looked like new chrome, bearings tight and no deposits in ports.

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You would expect deposits with opti-1 at 100:1?

Joel

 

[bonnie john]

yes joel, no deposits ( to speak of ), and fouled plugs and mufflers a thing of the past

Quote:

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Quote:

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... pulled the engine to bits at 15 years after the rest of it fell to bits, bore and piston looked like new chrome, bearings tight and no deposits in ports.

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You would expect deposits with opti-1 at 100:1?

Joel

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[Shannow]

A lot of the oil is consumed, so I wouldn't worry too much within reason.

After reading A.G. Bell's book on modifying two stroke engines, I like to run rich enough that the exhaust is just oily.

(To my mind at least), that indicates that the oil is not being completely consumed, and makes it to all parts of the engine.

 

[wileyE]

many new small engines for reason of emissions use fix jets or anti tamper devices. The fuel to air mixture (rich-lean) is set at the factory using the factory recommended oil mixture (fuel to oil). Deviating too far from this can make the engine run slightly richer or leaner (air-fuel). Since two strokes can be somewhat sensitive to rich-lean changes run quality might suffer. So if the factory wants 50:1, an oil formulated and mixed at 100:1 might "work" but usually won't give the best results.

 

[Shannow]

wileyE, I've got to disagree (only a little).

Running richer oil mixes (to the point that the exhaust is wet) has never given me a "driveability" issue on fixed jet appliances.

Some oils come "pre-diluted" for improved mixing, and would effectively be a leaner oil fuel mix in service

 

[wileyE]

No problem Shannow every machine and oil acts different. If your running more oil it can act slightly leaner, which with twostokes can often make them run a little crisper. The increased combustion temps can often burn the oil off better resulting in a cleaner running motor.

Where I've seen issues is motors that spec 20;1 and you run 100;1 in them without tuning the mixure. They go rich and usually smoke and pipe drool more, even though one might think less oil would have been better.

 

[Shannow]

I agree on the magnitude that you are suggesting.

My 1:50 stuff usually ends up 1:30(ish), much less a difference.

 

[mtgrs737]

Jim5,

I run all my 50 to 1 engines at 32 to 1 and I don't experiance visible smoke after warm up or fouled plugs or oil dripping out the muffler or excessive carbon build up. You need to remember that oil in a two stroke is just passing through and it is important that there is enough of it hanging around long enough to ensure that there is no metal to metal contact. I have been advised by long time lawn professionals and long time small engine mechanics to "run a little more oil" than the manufacturers recomended 50 to 1 ratio. Also remember that more oil equals more power because of better ring seal, and the more oil the more additives like detergents, anti-scuff, anti-ware etc. As far as worring about the air/fuel raito being thrown off by the higher amount of oil in the fuel mix one only needs to remember that the air/fuel raito is by weight and not volume. I suggest you mix to what you feel comfortable with and give it a try, I think that you will be pleased with the results.

 

[rokky]

As far as I know, any carbuerated engine will run richer at higher altitudes, not leaner.

 

[Jim 5]

rokky,

You're right, and that's why I want to run a little more oil in the mixture which causes the engine to compensate for the altitude by running a little bit leaner than the altitude will cause it to run.

 

[Cujet]

Oil mixture ratio can and is used to fine tune jetting. The old thoughts on two stroke oil still apply. Even with new, synthetic oils. To a point, more oil lubricates better and results in longer engine life. Racing engines need 32 to 1 for proper lube with modern oils. Just ask any Kart racer how well the engines hold up with 50 to 1.

Also, more oil does result in more power. I have the experience and testing background to state this.

Now, for lowly yard eqpt, anything will work, these engines do not make any power.

I suggest 32 to 1 Mobil 2T racing, for longest life, lowest carbon and best power.

 

[Jim 5]

Thanks cujet. You seem to be one of the 2 stroke guru's here on Bitog and I was hoping you'd chime in.

I had done a fair amount of searching on the 2 stroke oil and had concluded the Mobil 2t was the one to get. Problem is when you buy a new Stihl, they'll double your warranty if you buy a six pack of 100ml stihl 2 stroke oil. Having bought a stihl chainsaw and leaf blower recently, I've got about 9 bottles left.

I have promised all of this stihl oil to my dad for his John Deere mower with some kind of B&S 2 stroke engine. I don't think he's too fussy about the oil he mixes with. He said he was very pleased with this engine though it doesn't start on the first pull anymore after 15 years (but it always starts on the second or third). Of course, I just found out he's never changed the spark plug or air filter in 19 years since it was new. On my next visit, I'm going to do that for him.

 

[MrMeeks]

Cannot find Mobil synthetic 2 stroke locally.

 

[Johnny]

Mobil quit making the 2t about two years ago. To bad as it was a very good oil.