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Thread: Carbs

  1. #1
    cheatin' piston popper addicted's Avatar
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    Carbs

    I learned some thing the past few days about my carbs.
    It was running like crap the end of this season, and was running lean, even with the HS needles 3 turns out. Compression is good.

    Pulled the carbs apart and found pieces of glass like chips laying in the screwdriver slot in the jets on 2 out of 3 carbs. Looks like it was varnish that was stuck under the horseshoe that holds the n&s in, and also from the fuel tunnel that connects the filter to the n&s.

    Tore everything apart, cleaned with a dremel and a small wire brush.

    Tested popoff. found 2 out of 3 n&s were leaking. . . just not from the needle, but from the 0-ring that seals the seat to the carb! I bought these in august!

    Then I realized that even with a trippple outlet fuel pump, the way the carb rack is plumbed with the return in the rear is still asking for trouble. That must be why my yamaha has the return on the gas tank side if the rack and only runs a single outlet pump feeding the rear. Just the way the engine sits on a small angle up in the front means that the fuel will not be forced to fill all 3 carbs and be returned out the top. It will take the path of least resistance out the back. So, I swapped the fuel blocks from carbs 1 & 3 and looped the hose to connect the return nipple. Now they will be fed from 3 individual lines, and the return is facing the fuel tank.

    I won't be able to verify this setup until spring, but it makes sense when I think about it.

    I'll post a pic later.


  2. #2
    ph2ocraft's Avatar
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    I'd like to see a picture. You really have to watch for the crap that gets into the carbs via the tank, hoses etc. it can ruin a day pretty damn quick.
    In-line fuel filters are your friends!!

  3. #3
    cheatin' piston popper addicted's Avatar
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    The weirdest thing is that the gunk was from the inside of the tube that connects the filter to the n&s. The filters were spotless! I actually had to scrape the sh1t with a dentist's pick from inside that tube, and under the "horseshoe".

    Diddn't take pix if the crap. Sorry, but It slipped my mind. I do have a pic of the new fuel routing. I'll put it up later.

  4. #4
    ph2ocraft's Avatar
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    Did you ever get those pictures? I'm still a little lost in regards to the fuel taking a different route and not filling the one carb.

  5. #5
    cheatin' piston popper addicted's Avatar
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    Sorry. I had it, just never got around to downloading them.

    Here it is. As you know, the fuel lines in stock trim feed and return in the rear. This is also on a downward angle when running, because the nose is usually pointing up. That means that theoretically, an air pocket could form and stay in the front carb.

    Besides blocking off the stock nipples, I switched the fuel block from carbs 1 & 3. That way the fuel enters from the rear or bottom, and leaves along with any trapped air from the front, or top. With this setup, I doubt that a tripple feed is necessary.

    Look at the pic of the stock carb setup from my raider 1100. You can see that a single outlet pentagon pump feeds a fuel rail in the same way, but the return is on the front. And that engine drinks way more gas than a polaris 750 ever could.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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