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Hello, I acquired a 1979 Yamaha SRX 440 premix that states on the tank that oil should be mixed at 15:1. It smokes like a coal train but runs great. Would it hurt it to lean it out a bit. Not only does it take a ton of oil, but the smoke makes me sick to my stomach. Is there any oil that doesn't smoke, or smokes less at such an obscene ratio? Thanks, JH
 

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Isn't the ideal stoichiometric ration of fuel to air 15:1..? I'm guessing your oil should be more like 40:1 or 50:1, but i'm not sure.
 

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Yeah, I think Megaman's right. I had a Yami SS440 and it was 40:1. Yours shouldn't be much different. Just a guess though.

Word of the day..."STOICHIOMETRIC"
 

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I bet you leave a haze in your trail with it mixed at 15:1!!! 40:1 sounds correct to me from what I remember.
 

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Originally posted by jmach
[br]

Word of the day..."STOICHIOMETRIC"
"Stoichiometric"= n. The quantitative relationship between reactants and products in a chemical reaction.

Oops, i was close. It's actually 14.7:1 ratio. (by the way, i'm NOT talking about the oil ratio)
This will help explain what i mean. I copied it from www.howstuffworks.com

In order to reduce emissions, modern car engines carefully control the amount of fuel they burn. They try to keep the air-to-fuel ratio very close to the stoichiometric point, which is the calculated ideal ratio of air to fuel. Theoretically, at this ratio, all of the fuel will be burned using all of the oxygen in the air. For gasoline, the stoichiometric ratio is about 14.7:1, meaning that for each pound of gasoline, 14.7 pounds of air will be burned. The fuel mixture actually varies from the ideal ratio quite a bit during driving. Sometimes the mixture can be lean (an air-to-fuel ratio higher than 14.7), and other times the mixture can be rich (an air-to-fuel ratio lower than 14.7).
 

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the oil ratio differs depending on the type of oil.regular 2 stroke oil could be a 20:1 ratio and fully synthetic oil might be 40:1.Long story short dont burn up your sled,check with the manufacture specs first.
 

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Sorry To burst your bubble guys, but all the literature i have also says 15:1 Here is a quote directly from my book.

"On all RT439 models built prior to 1980 fuel and oil must be premixed at a ratio of 15:1 before being poured into the fuel tank. Manufacturer recommends using Yamalube Two-Stroke Engine oil or a suitable equivalent."

So unless he has oil injection, which he obviously doesnt or he wouldn't be asking, the correct ratio is 15:1
 
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