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  1. #1
    spud's Avatar
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    Stock Carb Jetting on Lowell Ported 1390

    Wondering what you guys are using for jetting on stock carbs on a Lowell Ported 1390. Single pipe, Advent Yam 94, opened D plate, V-Force reeds, free flow tube, prok F/A's.

    Any input would be appreciated.

    Currently I have:

    115 Pilots
    2.0 N&S Black springs
    140 Mains


  2. #2
    Moderator DrewNJ's Avatar
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    Spud, I don't know if it helps any but I have a GK 1390, stock 1300 reeds, free flow tube, Riva flame arrestors w/outerwears, opened D plate, stock CDI, stock carbs.

    I'm running:

    115 Pilot @ 1.25 turns
    145 Main @ 1 turn
    1.5 N&S with dull silver springs.. 100 restrictor with the others drilled.

    It's a little rich for sure but I'm leaving it that way because we do quite a bit of cold weather riding and I'm tired of tuning carbs.. ..
    Doug

  3. #3
    philip_gpr's Avatar
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    A Lowell motor will run hotter than an equivalent Group K motor, so I would think you will need more jetting than a Group K motor

    so take the Group K jetting and go larger

    It seems everytime I give a lowell motor more fuel it makes more HP

    You might further lower the pop-off - up the N/S to 2.3 or 2.5 (though I realize going from a 2 to 2.3 doesn't make much difference) I think as a general rule we all tend to run the pop-off too high

    I am guessing on the jetting but you might try 117.5 / 150

    Here is the jetting on my Lowell 1530 with blackjacks

    Pilot 122.5
    Main 165
    N/S 2.5
    80 gram spring
    Last edited by philip_gpr; 07-22-2008 at 09:00 AM.

  4. #4
    All hail the Chief! fullboogie's Avatar
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    Jim, you know I have a 1300 with stock carbs and Lowell porting. Not sure if this will help, but this is what I run:

    115 lows
    130 highs
    1.5 n/s

    Been running this for 4 years and all is well.

  5. #5
    DRC 4 LIFE TheDome's Avatar
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    Quote Originally Posted by philip_gpr View Post
    It seems everytime I give a lowell motor more fuel it makes more HP
    That is very true....I actually tried bigger mains and different pop off and picked up 2 MPH this year. Should have done it last year.

  6. #6
    spud's Avatar
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    Thanks for the input. Interesting. These things sure are thirsty.

    Dave - I too have the ported 1300 with advent and V-Force 3's it runs really good with 115 2.0 N&S @ 135 mains low screws 1 turn, highs 1 1/2 turns

    This 1390 is a lot thirstier.

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