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  1. #1

    GP1200R carb rebuild: pop-off problems

    I'm rebuilding the carbs for a friend's GPR. I'm using the recipe from O'Sidebill. We have genuine Mikuni rebuild kits, the needle and seat sets are WSM though. On one of the three carbs the arm is noticeably below the body, and on all three needles the clip on top does not rotate easily. On the one I have tested so far, initial pop-off was at 32PSI, and sometimes it won't pop, just start leaking around the needle. Per the recommendation at I stretched the 95gram spring to get a pop at 42 PSI, the springs were noticeable shorter than the springs that came with the Mikuni kits. Should I be worried about the lack of a definitive pop? Also my plugs sometimes leak above 40PSI, what type of plugs have ohers used, are the available at Home Depot or something?

  2. #2

    Join Date
    Jun 2011
    what size are your n/s combo? are you running the stock breather or f/a's? you need to make sure the needle is saturated good while testing or you may have problems. use wd/40 for the test. also open the needle manually and squirt some wd/40 down in it to get underneath it before you test the carb. you may have a bad n/s eventhough it is new. i bought all my parts from atlantic jetsports and never had any problems. if i remember correct for the sbn44 and a 1.5 n/s and 95 gram spring the pop-off should be around 40-45 psi. if that pop-off is not right you can run the risk of a lean condition and engine damage. all pop-off settings should be equal for a triple carb set-up

  3. #3
    Yeah turned out my biggest problem was that I wasn't using enough WD-40, after I ditched the crappy WSM pop-off tester and used my compressor to pressurize the carbs I could add a lot more WD-40 and it worked much better. Also one of the new Mikuni ams was not bent properly, confirmed by putting old needle and seat back in and checking with both old and new arm. Reused one of the old arms.

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