Should I re-jet carb for ethanol gas? - Polaris ATV Forum
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post #1 of 5 (permalink) Old 08-23-2019, 01:59 PM Thread Starter
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Should I re-jet carb for ethanol gas?

A neighbor told me that I should consider re-jetting the carb on my 2004 Sportsman 400 a size richer because the amount of ethanol in the gas has increased since the machine was made and has the effect of running leaner than it should. Has it increased that much to warrant a re-jet? I live in CA and bought the machine used in 2008. The original owner bought it in CA. Anybody else hear about this?
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post #2 of 5 (permalink) Old 08-23-2019, 02:26 PM
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If it idles and runs fine, don't sweat it - but it may be improved a bit by adjusting the fuel screw and going up 2 sizes on the main jet, but only if the alcohol content is 15% or more - in fact 15% ethanol is not recommended by the mfg. 15% ethanol fuel will damage fuel tanks, lines, pumps, filters, petcocks, carb holders (intake manifolds) carburetors and fuel injectors in a relatively short time - as little as 30 days or less.

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post #3 of 5 (permalink) Old 08-23-2019, 10:26 PM
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You live in CA and run there. CA has many mountains. You can be running at sea level and in the mountains The higher you go in altitude the leaner you need to go with the carb jetting. Altitude will have far more to do then ethanol. What altitude was the carb set up for? It is a big problem here in CO. We can be running at 4000 feet one trip and at 10,000 feet another. Your engine will lose 3% of its power for every 1000 feet higher altitude. This is where the newer fuel injection really helps. Fuel injection was a god sent. We no longer need to change jetting. But the problem is that the power loss of 3% is never regained.
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post #4 of 5 (permalink) Old 08-24-2019, 10:27 AM Thread Starter
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It was purchased from a guy who used it at 4200 ft.. I am at 3400 ft. According to everything I have read, anything over 6000 ft. is considered "high altitude" where jet settings get leaner. However, I do use the quad to plow snow in the winter where it is usually colder than 40F. I also use it alot in the summer. The stock main jet at <6000 ft. is a 167.5, according to the factory service manual. The machine had a 172.5 in it when I bought it, so obviously the previous owner ran it in the winter alot too. Anyway, in regards to the ethanol affecting jetting, I can safely conclude that it isn't a real concern unless it goes above 10%, which hopefully, it won't.
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post #5 of 5 (permalink) Old 08-24-2019, 01:09 PM
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Around here they are pushing the 15% ethanol blends as a green alternative, better for the environment and so on. Hasn't been mandated just yet though. I avoid any ethanol in all my small engines. As stated before it is OK in a vehicle that gets used all the time (your car or truck) but for engines that sit for extended periods it isn't a good choice. If it is all you can get, add a fuel treatment like SeaFoam to every tank of gas. That helps counteract the bad effects of the ethanol.

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