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Thread: Explain Jetting For Me

  1. #1
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    Default Explain Jetting For Me

    I have a 2010 Tundra LT 550F. I ride in high country at about 3,000 feet several times per year pulling a heavy loaded sled for 15 miles at a time. Sometimes the snow is pretty deep pulling the sled and other times it is a fairly well packed trail. The rest of the year I run in elevations of 5-6 hundred feet. I never have any problems but am I in danger of burning my machine up with factory jets installed? Does the higher elevation use more fuel and oil or less fuel and oil than the lower elevation?

    My Tundra does seem to require a lot of warm up time with the choke in the half choke position at the higher elevations but then often times it is 25 to 35 below zero at the time.

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    Member mod elan's Avatar
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    Factory jets will not hurt you in the elevations you describe. Skidoo claims their baseline jetting is for sea level at -4F. I have not ever compensated with larger jets for temps below -4F. I do however drive a little differently when it is -20 and colder. A bit easier on the throttle and won't do any wide open throttle riding. The added choke (enrichener is actually what it is) is required in the colder temps because the carburation is a bit lean and needs the extra fuel during warmup.

    I guess you could say the higher elevation is making you burn more fuel than you need. This is because the air is thinner and proper tuning would mandate you to use smaller jets to be better calibrated for the higher elevation in the thinner air. Would this be beneficial for you? Only if you want to install the larger jets when you come back down to the lower elevation. My opinion is not to mess with it in the conditions you have described.

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    Quote Originally Posted by mod elan View Post
    Factory jets will not hurt you in the elevations you describe. Skidoo claims their baseline jetting is for sea level at -4F. I have not ever compensated with larger jets for temps below -4F. I do however drive a little differently when it is -20 and colder. A bit easier on the throttle and won't do any wide open throttle riding. The added choke (enrichener is actually what it is) is required in the colder temps because the carburation is a bit lean and needs the extra fuel during warmup.

    I guess you could say the higher elevation is making you burn more fuel than you need. This is because the air is thinner and proper tuning would mandate you to use smaller jets to be better calibrated for the higher elevation in the thinner air. Would this be beneficial for you? Only if you want to install the larger jets when you come back down to the lower elevation. My opinion is not to mess with it in the conditions you have described.
    What he said. It should all be explained in your owners manual or the jetting chart under the hood. Sleds are jetted fat from the factory because the factory has to take into account every possible situation from guys who like to keep their machines constantly tuned for weather/elevation or the joe who just wants to start, run like a wild man, and who never bothers to peek under the hood unless it is necessary.
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    For a given jet size... The lower the elevation, the leaner your mixture will be. The higher the elevation, the richer the mixture will be. The warmer the temperature, the richer the mixture will be. The colder the temperature the leaner the mixture will be.

    If you're jetted for warm and go to cold, you will be running rich. Rich will have less power and waste gas.

    If you're jetted for cold and go to warm, you will be running lean. Lean is dangerous to the engine.

    If you're jetted for sea level and to up to the mountains, you'll be running rich.

    If you're jetted for mountains and go down to sea level, you'll be running lean.

    Since these two items are inverse of each other and you generally have warmer temps at sea level and colder temps at elevation, the effects on jetting are lessened. If you were running in very warm conditions up in the mountains and were jetted for that and then you went down to sea level in extreme cold, you would risk blowing the engine. But it takes a pretty significant change to get to that point.

    If you're concerned about it, there are plenty of devices available that will allow quick manual or automatic jetting changes as the conditions change. Otherwise, jet it in for perfect at your lowest elevation and coldest temperature and live with a little rich when you go up high. At least you won't worry about engine damage, but always carry spare plugs.

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    Quote Originally Posted by JOAT View Post
    If you're jetted for warm and go to cold, you will be running rich.

    If you're jetted for cold and go to warm, you will be running lean.
    I believe you have these statements reversed. Cold air is denser making the mixture leaner while warm air is less dense richening the mixture.

    My experience with skidoo sleds is they have been closer to proper jetting out of the box than other brands. They can be used with no issue in the conditions described right from the factory. Fuel injected machines are great IF the factory tuned them properly to start with. Various machines over the years have struggled with this. Expensive to rectify if not.

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    Member JOAT's Avatar
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    Yes, you're right. Proof reading is key and I skipped that step. I flipped the warm and cold in those two statements, but have it right in the rest of the piece.

    The 2nd and 3rd paragraphs should read:

    If you're jetted for cold and go to warm, you will be running rich. Rich will have less power and waste gas.

    If you're jetted for warm and go to cold, you will be running lean. Lean is dangerous to the engine
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    I appreciate this information guys. I've usually had an old machine if any at all for many years and I rode in the vicinity of Fairbanks which isn't high elevation. For the past three seasons I do ride some at the 3,000 foot elevation like I said and I don't want to fry an $8,000 sled. I did have a new Motoski 250 Sonic made by Bombardier back in 1976 and I burned a hole in a piston playing around off of my trapline trails one day. Even though it was only a 250cc it required high grade premium gas as it was a little hot rod machine.

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