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  1. #1

    Carb Guru needed - Popoff for 98 GSX limited

    I have a semi modified GSX limited the has a GroupK head (100 octane) Fly racing FA's, Solas Prop. Break in period on new top end.
    I tried 170m, 85 pilot w/ 2.5 needle, Black spring. 1 turn out low, closed mag HS, 1/2 pto HS. The thing feels like it is running one 1 cyl. Horrible idle. OK midrange, and 6300rpm top end. (unajustable)

    To me it is excessivly rich, but I would like sme ball park numbers to start with while I wait for my new topoff tester to arrive.
    I am going to try 2.3 needle, 80pilot, 165 main...Unsure about spring...

    Please help

  2. #2
    SURFnTURF's Avatar
    Join Date
    May 2007
    Assuming the engine is ok and the fuel lines are all good and adequete fuel is getting to the carbs.I would say your pop off is way too low using the 2.5n/s . I like 18-20psi prefer lower than higher.

    I like to use 167.5 mains , 87.5 lows with stock N/seat and stock spring.You can go larger on the N/seat if you like (some do, some dont). Highs closed and lows 1.5 turns out with accelerator pumps all working correctly. The 2.0 N/seat flows more than enough fuel for your application.
    To see if its rich do a plug chop test on the water, only way really if you dont have an egt guage. If revs are still low you might have a rave valve problem or water box control valve that is faulty.

    Pop off Chart below.

    115 gram = gold spring
    95 gram = dull silver spring
    80 gram = black spring
    65 gram = shiny silver spring

    115 - Mikuni Reference Number 730-03030
    95 - Mikuni Reference Number 730-03033
    80 - Mikuni Reference Number 730-03027-T
    65 - Mikuni Reference Number 730-03027

  3. #3
    Is the 65 gram spring stock?
    My main concern is the idle. It is running so rough at idle, even down to almost closed. Mid to high end accel good, but I think going from 170m to 167.5 will improve that adjustability, and bring my RPMs up.
    I will lower the needle seat to a 2.0.

  4. #4
    Stock spring is 95g

  5. #5
    aseymore aseymore's Avatar
    Join Date
    Aug 2008
    I think when you put a 2.0 n/s you will be able to adjust every thing out a lot better. Like someone said a 2.0 will feed your engine with all the gas it can handle. So many think that a larger n/s will do wonders when it is the other way around.

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