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3500 rpm flat spot?

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  • 3500 rpm flat spot?

    I have rode motocross all my life. I recently bought my first street bike, a 97 Katana 750 with 11k miles. The bike has to be choked slightly to get started and takes a while to warm up, I think I can fix this with a washer on the needle or an adjustable needle. My main problem is a flat spot between 3500 and 4200 rpm, after that it pulls really strong, I'm not really familiar with this type of carb and was wondering if it was a jetting issue. It has a 4 into 1 slip on under it and a Honda silencer?? (I'm not sure how that happened, it was like that when I got it). I am also checking the compression this evening and changing plugs, if there are any suggesttions on the best plugs. Any insight on this bike is greatly appreciated.

  • #2
    If the 750 is like the 600, 4k is when the main needles should start to move and let the main jets start working. I had a similar flat spot stock and an Ivan's jet kit cured it.
    - Beave

    1998 Katana 600 - Traded
    2005 F4i -


    • #3
      Thanks, I thought that would be the case, but experience is better than a hunch.


      • #4
        a very good cleaning never hurts either. with a 4-1 exhaust it might already be jetted. a 5* advancer is a simple upgrade too
        99% of the questions asked here can be answered by a 2 minute search in the service manual. Get a service manual, USE IT.
        1990 Suzuki GSX750F Katana
        '53 Ford F250 pickumuptruck
        Lookin for a new Enduro project


        • #5
          Shimming the needles won't help warm-up time . But it MAY help the low/mid rpm weakness ....
          Best plugs are stock plugs . NGK JR9C .
          Has the bike been jetted ? Check it out . Many just turn screwdrivers and hope for the best . Also look at the bottom of the slides to see if they've been drilled/tapped . I had to fill mine in and re-drill them the right size because of the aforementioned .
          I am a fluffy lil cuddly lovable bunny , dammit !

          Katrider's rally 2011 - md86


          • #6
            If I were a betting man, I'd say the owner took the jet kit out of the bike and sold it seperately before you bought the bike from him.
            90% of motorcycle forum members do not have a service manual for their bike.

            Originally posted by Badfaerie
            I love how the most ignorant people I have met are the ones that fling the word "ignorant" around like it's an insult, or poo. Maybe they think it means poo
            Originally posted by soulless kaos
            but personaly I dont see a point in a 1000 you can get the same power from a properly tuned 600 with less weight and better handeling.


            • #7
              take the K&N out and install factory AF

              I dont have "hobbies" I'm developing a robust Post-Apocalyptic skill set....



              • #8
                Don't have a K&N,,,, Do have an AR-15 (and others) though, and I agree.