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  1. #1
    cheatin' piston popper addicted's Avatar
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    need jetting advice from the experts??????

    here's the backstory http://www.greenhulk.net/forums/showthread.php?t=23394

    Basically running a 1mm over 750 with flame arrestors and boyesen reeds. 130 psi on all jugs.
    75 pilot (stock)
    110 main (90 is stock)
    LN 1.75
    HN 1.25, 1.5, 2.5

    I know that the low needles should be around 1 turn out, so how far do I jet the pilots up? 80's or 77.5's? Stock setting should be 1/2 turn out.

    what about the mains? rear and center have good wash. Front has almost no wash. weird thing is that it runs well, pulls hard and tops out at 6400 rpm.

    All the carbs are clean with fresh mikuni rebuild kits as of this winter.

    Running the 780 tripple pump with the return restrictor.

    Any ideas? this thing does not seem to conform to the normal rules


  2. #2
    It's kinda strange? I didn't mess with low jets but bumped my highs about 5 when I did my mod's 650 and soon to be a 750 so I set up my new carbs the same but anyway I had no prob getting in range! I did notice that the adjusters have a lot of range are you all the way out yet ? and do you only have the one coated piston??Z EDIT! not that I'm a pro! lol
    Last edited by ZMANN; 05-20-2007 at 11:38 PM.

  3. #3
    cheatin' piston popper addicted's Avatar
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    The low's do have more range, but everywhere I look it seems like the ideal way to jet them is so that the high and low needles are 1 turn out. I think it makes it a little more accurate metering the gas through a fixed jet rather than a tapered needle

  4. #4
    PolarisNut's Avatar
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    Quote Originally Posted by addicted View Post
    The low's do have more range, but everywhere I look it seems like the ideal way to jet them is so that the high and low needles are 1 turn out. I think it makes it a little more accurate metering the gas through a fixed jet rather than a tapered needle
    Remember though, that the jets and the needles adjust different parts of the fuel curve. The low speed needle adjusts idle only, where the low jet is from 1/8 to about 1/4 throttle. The high speed jet adjusts from about 1/2 throttle to 3/4 throttle, where the high speed needle is from 3/4 to Full. These numbers arent exact, but give you an idea. When all 4 adjustments are correct, you should have a seamless throttle transition.

    The low speed needles need to be adjusted to give you a good steady idle, without allowing the motor to load up. This setting will vary for a given motor and be dependant on ring seal, atmospheric pressure, idle rpm, temperature, etc.

  5. #5
    cheatin' piston popper addicted's Avatar
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    Right. I think I am compensating for an undersized pilot jet with a very opened low needle because if i only use the low needle for the idle, it lean hesitates when I nail it. Also, don't forget that the high needle also affects the transition that's something I learned from the watcon tuning sheet and it made a huge difference in my tuning results.

  6. #6
    PolarisNut's Avatar
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    Quote Originally Posted by addicted View Post
    Right. I think I am compensating for an undersized pilot jet with a very opened low needle because if i only use the low needle for the idle, it lean hesitates when I nail it.
    Yup, sounds lean on the pilot/low jet...

  7. #7
    cheatin' piston popper addicted's Avatar
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    I'm going to try a 80 pilot and see what happenes. Does anyone have any idea why I need so much gas on a mostly stock motor? or better yet, does anyone have a pic of bone stock 750 piston wash? Maybe they are supposed to be on the lean side?

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