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Backfiring after carb cleaning question

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  • Backfiring after carb cleaning question

    Looking for a little guidance from the Katrider gurus!

    Things have gotten fairly busy at work and I didn't ride my Katana for almost 9 months so of course when I got around to it the carbs were fairly gunked up and the bike would only run on choke. I decided to do a full carb cleaning and install new plugs and a jet kit while I had everything apart. Thanks to the awesome detailed guides on this site and some video walkthroughs I was able to get everything apart, dipped, and reassembled in a week. After synching up the carbs with some gauges I bought on ebay I put the tank back on and went for a test ride. The bike ran better than it's ever felt but once warmed up was idling to high. I pulled over and reduced the idle but couldnt get it started again due to a weak battery. After an overnight charge I started her up again and its running but seems to pop or backfire on deceleration. I would appreciate any advice or steps to trouble shoot from where I am now. I wonder if it could be a fuel issue as I still have some seafoam in the tank.

    The jet kit I used is Ivan's performance
    Stock air filter
    Stock exhaust
    A/F screws are 4 turns out
    Floats adjusted to 13mm
    --

  • #2
    Popping on decel means you are running lean. Where in the rpm range are you when this happens? Near red line? 8k+? 3-8k?
    1998 Katana 750
    1992 Katana 1100
    2006 Ninja 250

    2006 Katana 600 RIP - 130k miles

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    • #3
      Hmm....
      LOL I was going to say too rich.........

      By drawing too much petrol on closed throttle and burning the unburnt fuel in the exhaust

      4 turns out on the AF screw is about 2 turns too much and the float is also set a bit on the rich side if memory serves
      “Anything that happens, happens. Anything that, in happening, causes something else to happen, causes something else to happen.
      Anything that, in happening, causes itself to happen again, happens again. It doesn’t necessarily do it in chronological order, though.”
      ― Douglas Adams

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      • #4
        So to confirm, popping on decel is lean... not rich. Rich mix won't pop in the pipe, as the mix continues to be too rich and won't burn. Lean on the other hand will burn due to increase in temp of the exhaust and cause the flash burn or pop.

        That said... you mention Ivan's kit so I'm going to confirm your talking about a 98+ model katana. 4 turns out does sound way out, but that may be necessary to counter an issue that has been discussed here before for the Ivan's kit where new pilot fuel jets are needed on some models. That would cause a lean issue.

        Have you replaced any jets other than the main jets?

        Krey
        93 750 Kat



        Modified Swingarm, 5.5 GSXR Rear with 180/55 and 520 Chain, 750 to 600 Tail conversion, more to come. Long Term Project build thread http://katriders.com/vb/showthread.php?t=96736

        "I've done this a thousand times before. What could possibly go wron.... Ooops!"

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        • #5
          Sorry for the late response, been out of town all week. The bike is a a 98+ and I followed the specifications that came with the jet kit for the float adjustment and screw turns. I'll have to look into the new pilot jet issues Krey referenced as I only replaced the mains. I'll have to take it out for another test drive to see at which point the backfire occurs on decel, but I have not redlined it since installing the carbs so I would estimate below 5K rpm.
          --

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          • #6
            I do believe that a vacuum leak will cause back fire on decel too. I recently sprayed some Acetone based carb cleaner in my carbs, which ate the o-rings at the back of the intake boots. That caused a vacuum leak and it started back firing on decel and idling high at stop lights. Either the vacuum leak caused the backfire or the carb cleaner washed debris down the pilot jet holes.
            My Katana-1100 17" wheel swap
            http://katriders.com/vb/showthread.php?t=136894

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            • #7
              Originally posted by katanarider View Post
              I do believe that a vacuum leak will cause back fire on decel too. I recently sprayed some Acetone based carb cleaner in my carbs, which ate the o-rings at the back of the intake boots. That caused a vacuum leak and it started back firing on decel and idling high at stop lights. Either the vacuum leak caused the backfire or the carb cleaner washed debris down the pilot jet holes.
              Air/vacuum leaks and out of sync will definitely decrease the fuel flow, but increase the air... = lean. Yes sir!

              Krey
              93 750 Kat



              Modified Swingarm, 5.5 GSXR Rear with 180/55 and 520 Chain, 750 to 600 Tail conversion, more to come. Long Term Project build thread http://katriders.com/vb/showthread.php?t=96736

              "I've done this a thousand times before. What could possibly go wron.... Ooops!"

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