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Hello, so I recently bought a 1993 Sportsman 400 off marketplace and I was wondering if it was a 2-stroke or a 4-stroke? On the gas cap it does not say that it needs mixed fuel and then on the front of it, it has an oil Tank. The last owner said he did not remember if it was 2 or 4 stroke because he didn’t use it for a couple years.... I was thinking it was a 4-stroke because it has the separate oil tank at the front. I just want to check before I put straight gas in it.
 

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The oil tank requires two stroke INJECTOR oil - make sure to use INJECTOR oil and try to always use the same brand of oil - mixing oils can have an undesirable reaction. The guy you got it off of LIED! You will definitely remember is it is a 2 or 4 stroke regardless how long it sets unused. He was probably a flipper and never ran it for his personal enjoyment. I suggest you take it to a mechanic and have it inspected to make sure everything is adjusted and set correctly, or get a service manual and do the inspection yourself.
 

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The oil tank requires two stroke INJECTOR oil - make sure to use INJECTOR oil and try to always use the same brand of oil - mixing oils can have an undesirable reaction. The guy you got it off of LIED! You will definitely remember is it is a 2 or 4 stroke regardless how long it sets unused. He was probably a flipper and never ran it for his personal enjoyment. I suggest you take it to a mechanic and have it inspected to make sure everything is adjusted and set correctly, or get a service manual and do the inspection yourself.
Well the guy seemed pretty honest but when I got it, there was oil mixed with the gas... so that's why I was wondering.
 

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Well the guy seemed pretty honest but when I got it, there was oil mixed with the gas... so that's why I was wondering.
Another indication the seller was not an operator - he would not have mixed oil with the gas if it was a four stroke, but if the injector was disabled or disconnected, then it becomes necessary to mix the fuel. Again, I suggest you take to a mechanic to be inspected.

As to the fuel - Polaris recommends 87 octane non-ethanol, 89 or better 10% ethanol - I use 91 octane non-ethanol as it is the only non-ethanol grade available in my town (one station, one pump ethanol free) - to get any other grade I would have to drive a minimum of 12 miles. If you use ethanol blended fuel, don't put any more in the tank than you will use in 3 weeks. After 21 days, ethanol blended gasoline begins to degrade which can cause hard starting, bogging and if phase separation occurs, the water logged ethanol will settle in low spots in the fuel tank and carb leading to fuel line and carb damage and non-start problems. Just use non-ethanol fuel of any grade.
 
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