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Vacuum Leak ????

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  • Vacuum Leak ????

    So I have been working on my Kat for some time now..

    I have cleaned the carbs and bench synced them. After that she would start but would idle kinda rough. I did the water test and splashed some water on each of the header pipes and they all were hot and sizzled the water off.. at this point the bike would rev to some point just not well and still sounded pretty rough...

    So i went ahead and changed spark plugs, the old plugs didn't look awful,didn't smell of gas or have any oil on them.. after the spark plug change the bike will start and idle fine now with no choke . But as soon as I try to give it any kind of gas at all it will die.. if i turn the choke up it will idle higher but will still die as soon as I twist the throttle in the least.... She will also rev up if I cover the intake with my hand. but again as soon as I touch the throttle it dies.....

    So my first thought was a vacuum leak .. So I had seen on the forum somewhere that you can spray carb cleaner around the boots and if the Idle raises then you have a vacuum leak. well I tried that and nothing..

    So if anyone has any ideas please let me know because I am at a loss.
    http://katriders.com/vb/showthread.php?t=132122

  • #2
    I think you're on the right track with vacuum...Someone else will chime in on model specifics but, some (all?) of these bikes have vacuum operated petcocks on them. So, if it isn't able to open enough to get the full flow of fuel, you won't have enough fuel.

    The main issue is not getting enough fuel. Is it because of the petcock or because of a blocked/pinched line? Something like an Auxiliary Fuel Tank will help you narrow down the problem. It would eliminate the tank/petcock and if you use a fresh fuel line, that too.

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    • #3
      So I had thought the same thing. So I turned the petcock to what i believe was prime while the bike was running, to eliminate that as a option and it still did the same ... I might have turned it the wrong way to reserve... I will have to try it again.
      http://katriders.com/vb/showthread.php?t=132122

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      • #4
        http://katriders.com/wiki/index.php?...e:Petcock.jpeg

        Did you make sure to set the air/fuel screws and floats?

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        • #5
          Yes I did.. I had to replace the o-rings on the air fuel screws.I have them turned out 2.5 times... So about right in the middle of the range.. I did not however check the float heights. But I did make sure that the float needle was set onto the float itself.
          http://katriders.com/vb/showthread.php?t=132122

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          • #6
            Float heights are critical for proper operation.
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            • #7
              So do you think that it just isn't getting enough gas??? and that is why as soon as I hit the throttle it dies... but would run higher RPM with choke?
              http://katriders.com/vb/showthread.php?t=132122

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              • #8
                My guess is that you actually may be flooding the motor. Try loosening up throttle cable as much as you can at carbs and at handlebars. Turn idle adjust way down. Start bike with as much throttle as necessary , then hold at "idle" with throttle with one hand and slowly up idle adjust screw until you can let off throttle without bike dying. This worked for me after bench syncing carb. I had to play with idle and choke to get proper setting there too.

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                • #9
                  What? I'd put my hand slightly over the filter and rev, does it run better or die? I had the same issue with clean and stored set of carbs, I tore them down for a quick clean and assembly. Worked well after.
                  "I'm sorry, I didn't mean to upset you when I called you stupid. I thought you already knew..."
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                  • #10
                    If you don't mind me asking, I am having a crapload of issues with my 04 Katana 600 and I noticed you mentioned the hand over filter. I have two sets of carbs, cleaned both, and the set I had on the bike would run like a monster when I had my hand obstructing the filter, full power smooth acceleration. Take hand out and whammo..all goes to shit. Got good idle but stalls on throttle...got smooth power, but shit for idle. What ended up being your solution because I never found a vacuum leak anywhere..sprayed my bike all over.

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                    • #11
                      Originally posted by elianator View Post
                      If you don't mind me asking, I am having a crapload of issues with my 04 Katana 600 and I noticed you mentioned the hand over filter. I have two sets of carbs, cleaned both, and the set I had on the bike would run like a monster when I had my hand obstructing the filter, full power smooth acceleration. Take hand out and whammo..all goes to shit. Got good idle but stalls on throttle...got smooth power, but shit for idle. What ended up being your solution because I never found a vacuum leak anywhere..sprayed my bike all over.
                      By placing the hand over the intake your increase the pressures that pull fuel from the carbs, and decrease the air flow. Basically... you richen the mix and this points out that the bike is running lean when your hand isn't over the hole.

                      Lean could be dirty carbs, aftermarket high flow air filter, or poorly tuned carbs (especially if an aftermarket exhaust of any type is added to the bike, even slip on). It could also be an issue with something blocking partially the air 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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                      • #12
                        I've had this problem also. Had rebuild the carbs and everything.. Problem still persisted. Then read about the airbox drain tube needing a cap/stopper or it may cause a vacuum leak into the intake system. Plugged that up and seems to idle better.

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                        • #13
                          Originally posted by Foreverever View Post
                          I've had this problem also. Had rebuild the carbs and everything.. Problem still persisted. Then read about the airbox drain tube needing a cap/stopper or it may cause a vacuum leak into the intake system. Plugged that up and seems to idle better.
                          Yep, that'll cause a big ol' air leak
                          Howdy neighbor, welcome
                          1998 Katana 750
                          1992 Katana 1100
                          2006 Ninja 250

                          2006 Katana 600 RIP - 130k miles

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