2-cycle ratios

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SwedishRider

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I have multiple 2-stroke engines that all take a different fuel:eek:il ratio. One calls for 32:1, one calls for 40:1, and one calls for 50:1. How does one deal with such a range of ratios other than to mix 3 separate fuel containers? Shoot for the middle and run 40:1 in them all? I am using G-OIL Bio-synthetic 2-stroke oil and can mix it at pretty much any ratio I choose. What is my best course of action?
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My personal system is to setup everything to run on 32:1, because I always have a jug on hand for my dirt bike and atv.
 
It could, if you don't tune them for it. It can cause over heating from being too lean, and you will also lose power because of the incorrect fuel to air ratio.
 
With premix the oil displaces gas in the mixture, so less gas makes it through the carb. causing a leaner air to fuel ratio. But yes, it is a more concentrated oil to fuel ratio.

You have to adjust the fuel metering of the carb. to compensate.
 
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From what I've read, back in the days of two cycle racing motorcycles, 32:1 was the ideal ratio for making power and keeping the engine sufficiently lubricated. Those old air cooled two stroke race engines were making huge horsepower for their size and running at ridiculous rpms. They were flogged mercilessly for the entire race. However, the carbs were jetted to run 32:1 fuel.

What needs to be understood is that as you increase the oil in the mix, you're effectively leaning out the fuel to air ratio. Oil in the mix displaces gasoline thus creating a slightly lean condition. Can't say how significant of an effect that would have on a modern engine.

Modern carbureted engines are set so lean they're already on the edge. With that in mind, you might be better off keeping the ratio closer to 50:1 just to ensure they don't run too hot. Being a modern oil, 32:1 engines will likely run just fine if not better at 50:1 using a good quality two cycle engine oil.

I'd probably run 50:1 across the board.
 
Thank you both for the explanation. It makes more sense now. I guess I will mix a container of G-OIL 50:1 and run it for all three engines.
 
Some studies have shown that either 20:1 or 16:1 make the most power (I don't remember which, I am thinking 16:1). I think the extra oil helps the rings seal.

From my experience the smaller the engine, the more sensitive it is to the fuel mixture. Running 50:1 in a engine tuned for 32:1 may be safe, but it may hurt the performance.

I know some of the older Lawn Boy mowers that used bushings instead of bearings say to run only 32:1.

I have seen some ads lately for a new Husqvarna saw that claims to have a self adjusting carburetor.
 
Originally Posted By: AVB
With premix the oil displaces gas in the mixture, so less gas makes it through the carb. causing a leaner air to fuel ratio. But yes, it is a more concentrated oil to fuel ratio.

You have to adjust the fuel metering of the carb. to compensate.


It's probably a bit denser, and affects metering that way...the oil burns (mostly), so is still fuel for the large part.

I personally prefer my two strokes to have an oil damp exhaust, so that I know that the oil is getting all the way through the cycle.

A.G. Bell in his book two stroke performance tuning found more power always with richer fuel/oil mixtures, until the exhaust was overly wet.

will try to dig it up this evening.

http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=2224300&page=1

Edit link in thread is bust...will try to find another one, or copy the portion on oil mix.
 
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I have often wondered about the oil acting as fuel, how much it varies for different oils and how it affects the cooling properties of the fuel.

I like to have a wet exhaust too, we call it "splooge".
 
Originally Posted By: AVB
I have often wondered about the oil acting as fuel, how much it varies for different oils and how it affects the cooling properties of the fuel.

I like to have a wet exhaust too, we call it "splooge".


I think we're overestimating the effective contribution that the oil provides as fuel in a combustion chamber. If it were of such significance as a fuel, there would be no concern nor consideration for adjusting the carb to deal with the fuel mix ratio. In addition, if that much of the oil is burned off, it's lubricating effects would also be much diminished.

If your car is burning oil, does your fuel mileage improve?

Between 32:1 and 50:1, I'd say we're splitting hairs. However, as previously stated, with modern oils, I'd probably run 50:1 in everything.
 
I really haven't developed an opinion on the oil's contribution as fuel. It is just something I wonder about, but mainly what effects different oils have.

One of my favorite oils is Castor 927, I don't know if it would be considered a modern oil. I guess you could say it is a modern version of old school bean oil. The only other oil I really use is Motul 800 2T.

One thing I can say is that I hardly ever have a fuel related issue using these oils. Even with prolonged storage and ethanol.

I will have to check out that book by A. Bell, I had one of Eric Gorr's books until I loaned it to a friend.
 
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I just looked at the bottles that I used before the G-OIL, and they were also a 50:1 ratio. I've used them for some years now without issue in all three engines (without ever really thinking about it).

Seems a 50:1 mix is the way to go. I believe that's 2.6oz of G-OIL 2-stroke to 1 gallon of gasoline, correct?!?
 
The heavier ratios are just like when everyone used heavy oil in their cars. Oils weren't as good.

Now if you use a good oil 50:1 is more than enough oil. I think stihl did a study that showed that their ultra was good at almost 100:1.
 
Originally Posted By: jhellwig
The heavier ratios are just like when everyone used heavy oil in their cars. Oils weren't as good.

Now if you use a good oil 50:1 is more than enough oil. I think stihl did a study that showed that their ultra was good at almost 100:1.


Just like with anything else, it depends on the application, how you intend to use it, and what you consider is good enough. This is just my estimate, but for 90% of the population 50:1 with any decent oil is just fine.

For me, I am happy with the results and the convenience of running 32:1 in everything.
 
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