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  1. #1
    82elley's Avatar
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    Jun 2014
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    jensen beach, Florida
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    needle and seat ? 04 xlt 1200

    Ive run out of funds im using osisebill's jet and adjustments. Ive removed the accelerator pump and choke plates, modified the air box. Will 1.2 seats work or do I have to cough up another 60 bucks for 1.5's? Any thoughts would be greatly appreciated.


  2. #2

    Join Date
    Jan 2006
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    Texas City, Texas
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    Based on my limited knowlege of carbs, this is what I think.

    When you modified the air box, you potentially will begin to develope a lean hesitation. Not only that, but when you removed the accellerator pump, you most definitely created a lean spot in the mid range. The Mikuni "I" type carbs (which is what you have in your 1200) has a lean spot in the mid range by design..... for EPA testing purposes. The accellerator pump helps to get past that point by dumping extra fuel in the mid range while accellerating. So IMHO, if you were to put your carburation system back together as you described.....(removed pump, choke plates and modified air box), and I am assumeing that you did not change your jets, you would hesitate on the bottom end and potentially burn up a piston in the mid range.

    The larger pilot jet (110) and the 1.5 needle and seat help to eliminate hesitation by dumping the right amount of fuel through the bottom and mid range. The larger mains help to cover mid range lean spots and supply fuel all the way up to about 7/8's speed.

    The 110 pilot, 1.5 needle and seat, 95 gram spring and 120 main (125 main for those who have removed the choke plate) is a well documented, tried and true combination if you decide to go after market. You will do well if you follow this combination and do not deviate.

    Go to www.Mikuni.com and read on tuning of the Super BN 44carbs. There is a lot of interesting reading.

    I'm certainly not OsideBill, but hope this helps anyway.

  3. #3

    Join Date
    Aug 2006
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    I have done the O'Side mods to several boats and have done 2 XLT's using the 1.2 seats. Bill told me it would be fine if I fine tuned the springs. These new Mikuni springs are all over the place as far as pressure, you may have to stretch them a bit or squeeze them to get the pop off right anyway. In other words there is enough difference in the springs as received as there is in difference between a 1.2 and 1.5 seat. I set my pop off on both XLT's that I used the 1.2 seats on at 47.5 psi and both boats run perfect, boat in idle zones as well in accell and over 60 mph on gps, for the last 3 seasons. No issues. (I am at 850 ft above sea level)

  4. #4
    82elley's Avatar
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    Jun 2014
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    jensen beach, Florida
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    I have followed that formula to the t. Im out of funds for the flame arestors. I did drill the bkx and removed the inlet pipe. I'm planning on splashing tomorrow and see how it runs. Thks for the input guys! Hope im not blowing this forum up with issues tomorrow.

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