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  • New Bike Owner

    Hi, I'm a first time katana owner and also a first time bike owner. I've been having a horrible time trying to figure out an issue with my 2000 750. When I got the bike the guy trailered it a couple hours here and we unloaded it and fired it up. I was told it has a problem with one cylinder misfiring and you could tell by the way the bike was running, the guy said he had done a carb clean before because the bike sat for a while and has been having trouble ever since.

    Since then I've tried to start it a couple times, the first time it just turned over forever but never even showed a sign of firing, tonight I decided to take a look at the carbs and see if anything was out of the ordinary. I was in auto mechanics for a lot of years but here's where my illiteracy with bikes really shines, I have zero idea what it's called but every carb has kind of a block off plate that acts like a plunger, I could push them up and you could hear the diaphragm pushing up with it. Every one acted fine except for one, I could move it up about 1/8th of an inch before I could feel binding and couldn't open it any more. So I opened up the top of the carb and couldn't find anything out of the ordinary, I put it back together and it operated fine, I'm guessing that the spring may have been off of the alignment peg in the centre of the cap or something and that why I didn't notice anything out of the ordinary. Could that be the cause of the miss on one cylinder? What are those for on these bikes?

    Also after putting everything back together I tried to start it again and actually got a sputter out of it but then that quit and it went back to turning over with no luck, anything to check on this thing before I dive into checking the ignition system? Thanks for any help.

  • #2
    Sounds to me like the carbs are gummed up, most likely the pilot circuit. If not properly stored they will gum up quickly with our current fuels. Those plates are called slides, it's what operated the main jets through the needle you see coming off the bottom of it. The needle it tapered specifically and at a certain length to properly control fuel release gradually starting at 3000 RPM. To test my theory, attempt to start the bike, then pull the plugs... Are all of them wet? What color are they? Answer those and we'll have a better picture on where to go next. Like possible coil voltage and testing.
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    • #3
      Are you using the choke lever when trying to start the bike? Are you setting the petcock to prime also? (do not leave it on prime, leave it in the on position normally).

      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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      • #4
        Thanks for the help so far, I'll check on the plugs tonight after work.

        Should I be putting it on prime to start? The bike has an airbrush job done on it so the labels for the fuel switch are gone, but I've been using the 6 o'clock position which I read somewhere is the on position.

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        • #5
          http://katriders.com/wiki/index.php?...e:Petcock.jpeg

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          • #6
            Being an auto tech too, for 15yrs....10yrs ago If it was a misfire I always tried to determine which cyl/s were not firing by pulling fuel injector harness or spark plug wire one at a time if idle doesn't change you found it or simply by spraying the exhaust at each cyl with a spray bottle. Now we have those fancy infrared temp sensors.
            I'd rather see those results first rather than digging in the carbs first. If you believe it's the carbs than clean them all paying closer attention to the troubled carb

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            • #7
              Ya I was an auto tech for 14 years before moving up into management, the circumstances of the misfire sounds like a fuel issue more than a spark issue so that's why I started looking at the carbs, the cylinder that's misfiring is the same cylinder that had the stuck slide that's why I was asking about that. The previous owner was having a misfire after it sitting, did a carb clean to the best of his ability and after reassembly the misfire moved cylinders so it's hard to say if he did something wrong with them, he didn't notice the binding slide so it's hard to say what else he may have missed.

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              • #8
                Alright, so today I dug back into the bike, all the plugs were bone dry, clean and sparking perfectly so I went back to the carbs, I check the petcock on the tank and it worked fine, check the lines, the fuel filter, everything was operating properly. I watched the final length of line going to the fuel rail and the level inside the line wasn't going down while cranking the bike over, so I tilted the line and poured gas into the centre 2 carbs that the line could reach, cranked it over and it fired right up, not only that, it didn't even have the misfiring problem anymore, it ran awesome without the tank on with just the little splash of fuel in 2 carbs. My next step will probably be just replacing all of the fuel lines to the carbs and a new fuel filter but is there anything on the carb assembly that I should be looking at?

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                • #9
                  Originally posted by TA0502 View Post
                  Alright, so today I dug back into the bike, all the plugs were bone dry, clean and sparking perfectly so I went back to the carbs, I check the petcock on the tank and it worked fine, check the lines, the fuel filter, everything was operating properly. I watched the final length of line going to the fuel rail and the level inside the line wasn't going down while cranking the bike over, so I tilted the line and poured gas into the centre 2 carbs that the line could reach, cranked it over and it fired right up, not only that, it didn't even have the misfiring problem anymore, it ran awesome without the tank on with just the little splash of fuel in 2 carbs. My next step will probably be just replacing all of the fuel lines to the carbs and a new fuel filter but is there anything on the carb assembly that I should be looking at?
                  My Pre-98 doesn't use fuel filters. I considered using them but was recommended not to by someone here. Instead, they recommended sealing my tank with a tank cleaning/sealing product made by POR-15 (Do not use Kreem). Inspect how much crap/rust is in the filters to determine if you'll need to coat your tanks innards too.

                  I just replaced my fuel line with some 1/4" AutoZone fuel hose but it isn't formed, so I made them a little longer to make a more swooping bend as to not kink it. (Pre-98's use two fuel lines as the petcock outlet has two ports, plus the vacuum port.)

                  Verify that none of your rubber diaphragms on the carb slides are ripped, torn or have tiny pinholes. Definitely clean the main jet and pilot (idle speed) jets and carefully wipe down the needles of gum and varnish. The pilot jet has an axial thru hole that gets crap in it and clogs. Do not mess with any o-rings unless you have a rebuild kit to use with new o rings. I'd shoot cleaner and compressed air in all the jets and carb orifices. Good luck! Oh also, leave the four carbs mounted on the common rail or else you'll need to synchronize them to one another.

                  Originally posted by 92xjunker View Post
                  Sounds to me like the carbs are gummed up, most likely the pilot circuit. If not properly stored they will gum up quickly with our current fuels. Those plates are called slides, it's what operated the main jets through the needle you see coming off the bottom of it. The needle it tapered specifically and at a certain length to properly control fuel release gradually starting at 3000 RPM. To test my theory, attempt to start the bike, then pull the plugs... Are all of them wet? What color are they? Answer those and we'll have a better picture on where to go next. Like possible coil voltage and testing.
                  @92xJunker aren't there screws in the bottoms of the float bowls that you could crack open to drain carbs for the winter time? They seemed kind of accessible with a long phillips head screw driver....?
                  Last edited by dnelli; 07-28-2017, 06:03 AM. Reason: Automerged Doublepost
                  2004 KTM 525 EXC
                  2004 KTM 200 EXC
                  1990 Suzuki GSX600F
                  1978-1/2 AMF/H-D Low Rider 1200

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