# Oil mix mistake



## Macrocarpa (Apr 19, 2015)

Hi, all. This is my first post, although I've looked at many threads over the last few years. You might think I'm an idiot, but I poured enough Stihl Ultra oil to mix with 2.5 gallons. Unfortunately, my 1.25 gallon tank was nearly full before I realized my mistake. I added enough to get just under 1.5 gallons of gas. Would it be a mistake to use the gas with that much oil? I'll be using this in my FS 250 brush cutter -- won't be getting my Sthil saws out for a bit. I have a new plug and air filter to start the season. So, I'd have about 9 tank fills with the brush cutter on a ratio of about 30:1, rather than 50:1

Thanks, and hope you're not laughing at me!


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## sawfun (Apr 19, 2015)

I doubt you hurt anything except maybe plugged the exhaust a bit or at worst, fouled a plug. Better more oil than less. I run Stihl ultra at 32:1 in my fs250 like in my saws. 50:1 in the 4-mix engines. Just try to use a quality oil for saws and the real key is try to use ethanol free gasoline of any grade.


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## anlrolfe (Apr 19, 2015)

If you're worried, dump it in your truck and start over.
I'd probably just run it.


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## KenJax Tree (Apr 19, 2015)

Its fine just run it....worst case you foul a plug


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## CR888 (Apr 19, 2015)

Too much oil is better than too little, l would run it but be ready to richen your carb a little as its tuned for 50:1 so 30:1 will make the saw run noticably lean.(probably need 1/8-1/4 ccw) Just as long as you realize more oil in mix will make the carb fuel:air ratio leaner. Ultra is a good oil to accidently spill a bit too much into mix. I bet you really like your FS250....Stihl got that one right!


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## Macrocarpa (Apr 20, 2015)

Thanks for the ideas. I'll go with what I mixed by accident yesterday. We'll see what happens -- when the rain stops!

I do love the FS 250. It's a beast with the saw blade -- a great way to manage woods by whacking weeds, excess saplings, etc.


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## Marshy (Apr 20, 2015)

CR888 said:


> Too much oil is better than too little, l would run it but be ready to richen your carb a little as its tuned for 50:1 *so 30:1 will make the saw run noticably lean*.(probably need 1/8-1/4 ccw) *Just as long as you realize more oil in mix will make the carb fuel:air ratio leaner*. Ultra is a good oil to accidently spill a bit too much into mix. I bet you really like your FS250....Stihl got that one right!


Can you please explain why this occurs? does the viscosity of the oil/gas mix have a hard time getting through the carb jet and so less charge is delivered to the cylinder with the same amount of air?


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## KenJax Tree (Apr 20, 2015)

Marshy said:


> Can you please explain why this occurs? does the viscosity of the oil/gas mix have a hard time getting through the carb jet and so less charge is delivered to the cylinder with the same amount of air?


Exactly....so as your mix gets richer the air/fuel mixture gets leaner.


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## Marshy (Apr 20, 2015)

KenJax Tree said:


> Exactly....so as your mix gets richer the air/fuel mixture gets leaner.


That is not an explanation, your just saying the same thing that I highlited in bold but with different words.

What mechanism is at work with causes a decrease in the amount of fuel/oil to enter the combustion chamber (less fuel, same amount of air = leaner) or an increase in the quantity of air (more air, same amount of fuel = lean) such that the ratio of fuel/oil to air changed and cause the charge (air+fuel/oil) to lean out?


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## KenJax Tree (Apr 20, 2015)

You answered your own question....less fuel and same amount of air, so by opening the jets you're letting more fuel in. When the amount of oil increases the amount of fuel decreases. The only way the air would change is if you get an air leak and it leans out.


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## Trx250r180 (Apr 20, 2015)

Marshy said:


> That is not an explanation, your just saying the same thing that I highlited in bold but with different words.
> 
> What mechanism is at work with causes a decrease in the amount of fuel/oil to enter the combustion chamber (less fuel, same amount of air = leaner) or an increase in the quantity of air (more air, same amount of fuel = lean) such that the ratio of fuel/oil to air changed and cause the charge (air+fuel/oil) to lean out?



Way was explained to me was put a straw in a pepsi ,take a drink ,then put same straw in a milkshake and take a drink ,the thicker volume goes through the same straw but slower ,so it creates a lean mixture so so you would need a bigger straw /jet opening for the thicker shake to flow same speed .
Hope this makes sense because i confuse myself often ,but i am kind of craving a pepsi now .


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## KenJax Tree (Apr 20, 2015)

Trx250r180 said:


> Way was explained to me was put a straw in a pepsi ,take a drink ,then put same straw in a milkshake and take a drink ,the thicker volume goes through the same straw but slower ,so it creates a lean mixture so so you would need a bigger straw /jet opening for the thicker shake to flow same speed .
> Hope this makes sense because i confuse myself often ,but i am kind of craving a pepsi now .


Ditto but i want the milk shake


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## jughead500 (Apr 21, 2015)

You guys are funny.makes me want to fire up the fs250 and piss rev it with a heavy mix. Oooo hey guess what? Tomorrow is Earth Day! Hey macrocarpa let it smoke!


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## olyman (May 12, 2015)

KenJax Tree said:


> Ditto but i want the milk shake


 wrong. I want a choc malt...........


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## pjones (May 15, 2015)

Thats different from how I understood it. I thought air and liquid volumes stay the same but because you are reducing the amount of combustible liquid and replacing it with oil it causes it to lean out. Maybe I am wrong but the viscosity of the mix would probably be very similar until you get more extreme differences so flow rates should be similar. 

For example: If your engine runs with 100% gas and you mix it with 50% oil then you are going to need to increase the flow rate to account for the fact that now the engine is only getting 50% of the fuel that it was previously getting.


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## KenJax Tree (May 15, 2015)

pjones said:


> Thats different from how I understood it. I thought air and liquid volumes stay the same but because you are reducing the amount of combustible liquid and replacing it with oil it causes it to lean out. Maybe I am wrong but the viscosity of the mix would probably be very similar until you get more extreme differences so flow rates should be similar.
> 
> For example: If your engine runs with 100% gas and you mix it with 50% oil then you are going to need to increase the flow rate to account for the fact that now the engine is only getting 50% of the fuel that it was previously getting.


Correct. Your mix ratio is richer with more oil but the air/fuel fuel is leaner, in other words more oil=less fuel in the combustion chamber.


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## nk14zp (May 15, 2015)

KenJax Tree said:


> Correct. Your mix ratio is richer with more oil but the air/fuel fuel is leaner, in other words more oil=less fuel in the combustion chamber.


Oil has more energy than gas so I don't buy it.


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## HuskStihl (May 15, 2015)

pjones said:


> Thats different from how I understood it. I thought air and liquid volumes stay the same but because you are reducing the amount of combustible liquid and replacing it with oil it causes it to lean out. Maybe I am wrong but the viscosity of the mix would probably be very similar until you get more extreme differences so flow rates should be similar.
> 
> For example: If your engine runs with 100% gas and you mix it with 50% oil then you are going to need to increase the flow rate to account for the fact that now the engine is only getting 50% of the fuel that it was previously getting.


The effect occurs because more oil does slow down the flow, not because there is less fuel. Best example of this is Belray H1R. If you switch to H1R, even with no change in ratio, you will need to richen quite a bit. Not because it burns less than the other oil, it has a different viscosity and flows thru the carb differently. BMX180r250pMS170 has it exactly right, but Pepsi is gross


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## HuskStihl (May 15, 2015)

nk14zp said:


> Oil has more energy than gas so I don't buy it.


If you don't buy oil, you are likely an unamerican commie!


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## HuskStihl (May 15, 2015)

To the OP, do you own a larger gas can, or a second small one?


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## Wood Butcher (May 16, 2015)

I wouldn't say that Pepsi is gross, but I sure siphoned enough gas in my misspent youth that reading about sucking Pepsi through a straw in a gasoline thread is gross because from just reading that I now cannot get the taste of gas out of my mouth! 

Regarding the initial question, as mentioned you might have to adjust your carb but long ago I worked for an OMC dealership and we as standard practice doubled the oil in pretty much all new 2 stroke engines so I doubt you will hurt anything.


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