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engine rpm bouncing rapidly while riding, mostly 5k+

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  • engine rpm bouncing rapidly while riding, mostly 5k+

    I've got a 94 Katana 600. I bought the bike used a few months back. I bought a Vance and Hines pipe, and a Dynjet jet kit for it. After getting these both installed, the bike seems to run oddly on the highways... well, anyplace for that matter. Basically it will start almost jumping, sort of like "vroom VROOM vroom VROOM", it'll seem to jump rpms maybe 500 up than down... This does not happen all of the time. I'm assuming there's been no maintenance done to this bike prior... Is there something obvious that I could look for? I'll probably take it to a shop, but I don't want to pay someone to tell me there's nothing they can do about it..
    oh ya. i've done the basics, changing plugs and stuff... i've tried different types of gas even. the carbs were cleaned out a few weeks ago, no improvement.

    thanks.

  • #2
    Hmmm. New jets. Carbs are almost impossible to rejet without a dyno. Here's a good link...

    http://66.47.68.116/tech/carbtun.html

    Go here, then go to the 'High RPM' page and read and weep!!! Good luck. 8)
    My first aid kit comes with lights and siren

    But sir, we are Navy SEALs, we are supposed to be surrounded...

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    • #3
      that might be it, the plce i took i to didn't have a dyno, not really sure what they did... but i'm thinkin i could have randomly stuck a new jet in and played with it also =]
      i might just call a shop and tell them whats going on, maybe it'll be something simple. i just didnt know if it could have been something in the engine or not. like, something seriously wrong in it, haha.

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      • #4
        no one has anymore opinions on this one? i'm hesitant to take it to a shop since a lot of them will say 'bikes too old to mess with!'

        thanks

        Comment


        • #5
          It might not be your carbs, coils do the same at higher rpm's when going bad. If you ease off the throttle does the bike smooth out? if so I garrantee it is the coils going bad.
          TDA Racing/Motorsports
          1982 Honda CB750 Nighthawk, 1978 Suzuki GS750 1986 Honda CBR600 Hurricane; 1978 Suzuki GS1100E; 1982 Honda CB750F supersport, 1993 Suzuki Katana GSX750FP. 1981 Suzuki GS1100E (heavily Modified) http://katriders.com/vb/showthread.php?t=94258
          Who knows what is next?
          Builder of the KOTM Mreedohio september winning chrome project. I consider this one to be one of my bikes also!
          Please look at this build! http://katriders.com/vb/showthread.php?t=91192

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          • #6
            the bike does smooth out when i left off the throttle... i can let off just a tad and it'll smooth out nicely... maybe i'll check into replacing that first. stupid question, but are the choils just the box that the plug wires plug into? or... i forgot what thats called, haha. ive never really had to mess with replacing much on bikes obviously.

            thanks.

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            • #7
              is there anyway to test the coils before assuming they're the issue? it sounds like it possibly is the coils... i was wondering if somehow they were pushing out the wrong voltage or whatever to the plugs and making them fire whack. they look sort of high to replace... i guess i could find a 'working' pair off ebay and see

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              • #8
                Originally posted by encieno
                the bike does smooth out when i left off the throttle... i can let off just a tad and it'll smooth out nicely... maybe i'll check into replacing that first. stupid question, but are the choils just the box that the plug wires plug into? or... i forgot what thats called, haha. ive never really had to mess with replacing much on bikes obviously.

                thanks.
                That can be carb slides or coils. More than likely, <and this is without riding or experiencing the problem personally> it is coils.
                TDA Racing/Motorsports
                1982 Honda CB750 Nighthawk, 1978 Suzuki GS750 1986 Honda CBR600 Hurricane; 1978 Suzuki GS1100E; 1982 Honda CB750F supersport, 1993 Suzuki Katana GSX750FP. 1981 Suzuki GS1100E (heavily Modified) http://katriders.com/vb/showthread.php?t=94258
                Who knows what is next?
                Builder of the KOTM Mreedohio september winning chrome project. I consider this one to be one of my bikes also!
                Please look at this build! http://katriders.com/vb/showthread.php?t=91192

                Comment


                • #9
                  it does sound more like an ignition issue than a carb problem. it was probably just bad timing that the jet kit was put on, and the coil/s were failing. i'm going to go ahead and replace them to see what happens. ronayers looks like around 140 or so for both of em.

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                  • #10
                    Just an update.. Before changing the coils on this thing, I've been trying other items that people have been suggesting. Basically, I've checked the carb sync, they were OK, I've lowered the floats to 15mm, they were right about 12mm. I'm hoping this will help it run a little leaner since it was running RICH as hell. Now I'm just waiting on some coils on ebay so I don't have to buy new ones.. Oh ya, after the float lowering and such, problem still exists... Now it's really sounding like a coil issue, unless there's some weird carb setting that I'm unaware of... the 'bounce' screw, haha.

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                    • #11
                      STOP.

                      Before you go any further, get a manual. Then whip out a multi-meter (hey I've got one here for $10 plus shipping) and test the coils. It's far easier to test them (and other issues) than it is to simply throw money at parts in the hopes that you will hit the right solution.

                      Cheers
                      =-= The CyberPoet
                      Remember The CyberPoet

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                      • #12
                        Encieno, when you say you lowered the floats, are you talking about when the carbs are inverted? If so, you richened the misture. If you "lowered" them while looking at them in their normal position (as installed on the bike) you leaned the mixutre. The suzuki manual will tell you proper float hieght is a set spec +/- 1-2mm.
                        If you wanna live life by your own terms, you gotta be willing to crash and burn!!!

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                        • #13
                          Sorry about that.. I actually raised them inverted, which would have lowered them if they were sitting normally. The plugs looked a lot cleaner after doing that. I also notice a lot LESS black smoke coming out the back when you rev it up... It was turning my exhaust pipe really dark also. So as of now, I'm assuming it's leaned up a bit... Still working on the idle issues.

                          CyberPoet: I did get a multimeter and checked the resitance in the coils, everything looked good on the primary side, but I couldn't get anything out of the secondary... I tried to check all sorts of ways. I know there's *something* there, but the meter just wasn't showing anything. I figure I would at least try the coils since if that's not the issue, I can just resell them on ebay... hopefully not losing money on the deal. I'm about out of ideas other than that... I've never really messed with engines like this so I really don't know what else could be causing this 'rhythmic' type of engine bouncing.

                          Comment


                          • #14
                            ok, SOOO, this sucks. i got the new/known good coils today, stuck em in, same thing... now i'm really lost, haha. i think it's gotta be something electrical, just by the way it seems to loose power... unless carbs could do that too, i'm really unsure. i think i might scrap it and get something else if i can figure it out soon. i'd hate to pay a shop $500 or whatever to fix it... i put a bit of money into it initially but hell, its starting to be like paying to put a new head gasket on an 89 geo, haha. just doesn't make sense!
                            anyone else have any ideas what may be causing this?

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                            • #15
                              After taking it to a local shop, the guy assured me it was a sync. or vacumm issue. Would a vacumm problem be causing this? How many places are there to check for vacumm? He said to spray some carb. cleaner around the carb seals, where it enters the chamber and see if the idle raises or not. I did that and didn't hear any difference really... I didn't try it with the tank off though... Would this be a possibility? Would replacing those rubber seals around the carb/chamber be a good idea? I'm hoping it's some simple problem out there, but after tearing it apart 10-15 times, I'm starting to lose hope, hehe. Anyone with ideas?

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