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Carb vacuum issue

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  • Carb vacuum issue

    Hi guys! I´ve had an issue with my ZZR D1 that I just can´t figure out, so hoping for inputs here:)

    If bike has been sitting for more than a few days, on cold start it will run on 3 for a minute or so, then starts firing on all 4. Sweet as anything after that, smooth as silk and everything normal.
    While servicing today I noticed that when pushing the butterfly valves up with my finger, there´s a slight resistance noticeable on 3 of them, but #3 has almost no resistance at all. Changed all butterfly valves a couple of years back and synced the carbs ok, so doubt the butterfly itself is faulty.

    How do I find any possible vacuum leak here? Isn´t this a matter of either they work or they don´t? (As in, leak vacuum valve or cover badly seated/ broken?)
    Would appreciate feedback:)
    Cheers, Egil

  • #2
    If the diaphragm on the slide has a hole or tear in it then it would act up the entire time it was running. About the only way to find which carb it is would be to hook up vacuum gauges to them and see which one isn’t pulling the same vacuum. Just a thought, it could be a blockage in your “enricher” circuit since it only does it on a cold start.
    Government's first duty is to protect the people, not run their lives.


    • #3
      Ok, this sounds stupid but have you been leaving the bike on the side stand? You state that once it clears itself it runs fine and also it happens when the bike has been standing for a while. I know of several people who had a similar issue. It seems to also happen when the fuel is 10% Bio which is sold in many countries now.
      ZZR Riders don't die, we just reach light speed!



      • #4
        I've had the same thing happen with my 99 R1, which also has CV carbs. It would start on 3, and the 4th cylinder would fire as the engine was warming up.

        This gradually became worse though, to the point where you would have to start riding the bike before it would run on all 4. It turned out to be caused by a leaking float needle valve, which caused that cylinder to run too rich at startup.

        The R1 has Mikuni carbs and the intakes are at a much greater angle than on the ZZR, so a leaking needle valve on a ZZR might not cause the same fault. But it did take a while before I figured that one out.
        "You don't get slower with age, you just get more cautious." Michael Rutter

        06 Ocean Blue ZZR1200, the coolest colour.
        99 Yamaha R1


        • #5
          Really appreciate inputs here, guys! Looks like I have to take them off and check them one by one. Cheers!