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  1. #1
    Hell Bent or Heaven Sent? Bent's Avatar
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    Carbs - why not slide types?

    I'll admit I'm only aware of the butterflys in the majority of what I've seen so far, but why didn't polaris pursue slide type carbs like their sleds?

    has anyone retro'ed a set of slide carbs on a Polaris?

    At least I have a slim chance of tuning them.


  2. #2
    XLTNoob
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    I'm not a polaris guy at all, so I'll speak from general experience.

    In action, snowmobiles generally sit at one plane. They rarely lean and never (hopefully) turn on their side or upside down.

    Jetski's are constantly leaning side to side, as well as up and down. They also flip over occaisionaly. This is all considered "normal" behaviour.

    The "Slide" type carbs that you speak of on the snowmobiles are actually called Variable Venturi carbs.

    In my experience, the Variable Venturi carbs rely on a fuel bowl on the bottom of the carb, and those rely on gravity to feed the bowls from the tank. Turn the snowmobile on its side and see how long it runs. (then look inside the engine bay and look at the spilled fuel!)

    On the other hand, Jetskis use diaphragm carbs. The diaphragm is used for fuel accessiblity, eliminating the issue of carb orientation. These can even work upside down! They also (usually) have two check valves on the other side of the carb, which works as a fuel pump. This eliminates the issue of gravity to feed the carbs from the tank.

  3. #3
    Bing-A-Ding-Ding-Ding, Brrrrrap! Brrrrrrrrrap!!! Polaris_Nut#1's Avatar
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    I wouldn't be surprised if I saw these diaphragm carbs on a serious snow cross sled.

  4. #4
    Hell Bent or Heaven Sent? Bent's Avatar
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    'seems to me the old Ski Doo TNT model (early 70's 340 cc engine) used titlotson carbs that were butterfly types.

    And - Fuxxy, you may be right about the diapham type theory, but I'll counter with this, how about dirt bikes - it seems they lean over quite a lot?

    HMM?

    O, BTW, Polaris Nut, congrats on 1000 posts.

  5. #5
    XLTNoob
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    You are correct, motorcycles do lean a lot. However, when they lean, centrifical force overcomes gravity and the fuel stays glued to the bottom of the bowl

  6. #6
    Bing-A-Ding-Ding-Ding, Brrrrrap! Brrrrrrrrrap!!! Polaris_Nut#1's Avatar
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    Quote Originally Posted by Bent View Post
    'seems to me the old Ski Doo TNT model (early 70's 340 cc engine) used titlotson carbs that were butterfly types.

    And - Fuxxy, you may be right about the diapham type theory, but I'll counter with this, how about dirt bikes - it seems they lean over quite a lot?

    HMM?

    O, BTW, Polaris Nut, congrats on 1000 posts.
    Thanks Bent, I would have missed it. I hear ya on the dirt bike theory. I'm guessing it had to do with if the craft were to tip upside down for any period of time. I know if I tip my 250R over it will flood it. Wouldn't be good in the middle of a lake or ocean.

  7. #7
    axgrider73's Avatar
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    Kawasaki Ultra 150's use a slide type carb. The provide a very smooth throttle response.

    The biggest problem most people have with them is trying to put after market flame arresters on them. It will make a lean condition that cannot be corrected by jetting.

    The slides are controled by vacuum, and when you put a free flowing F/A on it disrupts the vacuum inside the venturi.

    Not to mention that the rebuild kits are $120 each.

    However, I might be selling mine in about a month if you want to give them a shot.

  8. #8
    SPEED KILLS, BUT YOU GET THERE QUICKER Keddano's Avatar
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    I would have to say the std brass floats in a slide style would get knock out off wack often from the G-Force of slam on waves.(float height) Bikes don't normally face the impact that a ski does.

  9. #9
    ph2ocraft's Avatar
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    All valid reasons and if I'm not mistaken somebody tried them on a watercraft and wound up dead due to the fuel left in the bottom of the hull after a roll over.

  10. #10
    race24x's Avatar
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    PH2O so far thats the only valid reason I can see. A dirt bike takes just as much abuse riding motocross and jumping etc as a water craft, but are only upside down for a very very short instant (from what I have seen on TV anyway LOL)

    AXG I am not sure why they would have trouble my slide type carbs went from an airbox to a stage 3 jet kit (open air filters) and I had to change some things in the slide and jetting as well as needle profile but it ran very well

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