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  1. #1

    Join Date
    Aug 2007
    Long Island NY

    Mikuni BN46I carb rebuild

    Just rebuilt 4 Mikuni BN46I carbs, 2 from 98GSX and 2 from 99XPL. Rejetted and removed chokes. When testing pop off pressure with Main diaphragm and cover installed, needle won't hold pressure and pop off won't test on any of the 4 carbs. If I do the test with the main diaphragm and cover removed needle holds 10psi and pop off checks at 20psi. Book calls for 19-23 psi. New diaphragms seam stiff compared to old ones that are like tissue paper.
    With all the choke junk removed and the choke shaft holes plugged, and the accel pump removed, is it ok to use the orginial spray nozzles for the accel pump as my primer input?
    One last question while I have your attention: reed valve spacers help any? Both engines are fresh, first oversize, Miller heads, carb mods 85/167, carbon fiber reeds, solars impellars, waterbox bypass kit, Rev limiter set to 7500. 98GSX has a 4tec 10 vane pump.

  2. #2
    ive had dramas with wsm rebuild kits the same way, also make sure the arm is flush with the body of carb either side of the arm, good to check if the arm pivot is seated properly too,
    some say spacers dont work but if mel miller makes them use them, moves the reeds away from the crank turbulents and gives you more cc's to the cases

  3. #3

    Join Date
    Feb 2008
    Spray alittle lube on the needle and seat, they wont pressurize when dry.

  4. #4
    Moderator OsideBill's Avatar
    Join Date
    Mar 2006
    United States
    You have to use wd-40 even the mikuni manual suggests this. test pop-off with the diaphram and cover removed. put some wd-40 in and hold the needle open so it will drain into the fuel supply side, then do the test cover with a paper towel to minimize spray. Here is a copy of the Mikuni SBN manual that outlines everything. all thesame principals apply to this carb.
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