ZX600 c will only go 80mph
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Thread: ZX600 c will only go 80mph

  1. #1

    Angry ZX600 c will only go 80mph

    Last fall I over wound the engine once and it ran alittle rough when I put it away for the winter. This spring I was running around on it and it was doggy and wouldn't go much over 80mph. I put an ajustable set of needles and bigger jets. it is way quicker in first and second gear than it ever has been but it still only runs about 80. It felt like it was running out of fuel so I put a snowmobile pulser (vacum fuel pump ) on it and it still only goes about 80. I put new plugs in it and it still feels like it runs out of fuel or has a rev limiter still at 80. I ran 130mph last fall before I over reved it but It felt weak. It must not be fuel because I raised the float levels till they over flowed then backed them down till they didn't leak. Have any Ideas's??

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  3. #2
    Super-Fast Redneck Array jschapansky's Avatar
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    Jul 2003
    99' Yamaha R6 turned Streetfighter
    carb sync???
    2 wheels or 4 wheel drive

  4. #3
    no probably not carb synch. that mostly affects smoothness especially at idle. and fuel economy.
    If you over-revved the motor you *may* have a bent or chipped valve , if you over revved it enough to float the valves or your camchain had excessive slack.
    Do a compression check and see if that's the case. cylinder with a damaged valve will have a way lower compression than the rest.
    Or it could be something simple and stupid like a clogged fuel filter or dirty air filter.

  5. #4
    Moderator Array TeeTee's Avatar
    Join Date
    Feb 2002
    Out to pasture in the 'Wack
    04 Kawi Z1000,
    First off Welcome to BC Canada... We're really meant to be a local forum but it's nice to see folks from further away come in for a visit now and then.

    Not to slag you but from all the carb messing you've done with an obviously heavy hand I would suggest you just drop it off to some shop or mechanic that knows what they are doing. Carb adjustments are a touchy thing and they do not respond to such crass adjustements. Or if you want to do it yourself I suggest you go back to the stock or previous setup that worked well and start from scratch again. No way should you be moving the float level that far. Especiallly no way should you be messing with the carbs when it's far more likely the problem is related to the overreving you did.

    I also suspect that you bent something or blew something if it's running that badly. The bike would not go out of adjustment to the extent you describe over the winter unless you broke something in it. You should be checking the compression and valve clearances first before you mess with the carbs.
    A backyard mechanic without a service manual is just like a hooker without a lamp pole.... they are both in the dark.

  6. #5
    Registered User Array Commuter Boy's Avatar
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    May 2003
    Suzuki Bandit
    What were the plugs like when you replaced them? Do a search on the net
    for "plug chops" and maybe find out what your wide open throttle jetting is
    like. Perhaps it's a bit rich, which might have a lot to do with your floats being
    just low enough not to overflow.

    When you start adjusting stuff, only do one adjustment at a time, else you can't
    isolate what changes are affecting what.

  7. #6
    The plugs I removed had the electrodes burned back about even with the ceramic and the gap was out to .040. they where an Ivory white color. They are dark brown now with a #2 nearly black. I set the float levels back to normal it didn't change anything. I put the heavier springs in the diaphragms that just dogged out the bottom end alittle. i pulled the plugs again and did a compression test Plugs were still dark brown with #2 nearly black. The Compression was #1 73 lbs. # 2 53 lbs #3 102 lbs #4 93 lbs. it still would only buzz up to 80 then pickup speed super slow. I cloud run faster with 2/3 's throttle than full open.The bike always over heated when setting at a street light that didn't change for a long time. The bigger jets seemed to have cured that. I took it to the shop where I bought it and they sent it home with me so far out of wack it would barely start. they opened up the air screws only 2 turns . With these jets it likes 3 turns from 2 3/4 turns with the old jets. It starts better than ever has more off the line power than before. I think your right about the valves . Maybe the rings are weak ?? What is the compression supposed to be?? Thanks for the help .I'm from montana so your my neighbors.

  8. #7
    Supporting Sponsor/Vendor Array Talon's Avatar
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    Jan 2005
    DT Vancouver
    Husaberg FE390 / Honda CR500
    New engines should run about 140 - 160psi give or take. 53psi is rebuild low. Also white on a spark plug is Bad News, you may have cooked 'er and i would blame the lean running engine for the overheating problem. Could be from a plugged fuel filter. The new jets may be too big though, heres why.

    Consecutive low compression in all cylinders could mean that the problem of fuel washed cylinders exists. This means that the engine has had too much fuel introduced into it and all of the oil has been washed off the cylinder walls. The oil creates a sealing effect between the piston and ring assemblies and the cylinder walls of the engine block. Without this thin layer of oil, the engine compression would be allowed to escape into the crankcase.

    You mentioned that it ran great in the lower gears, so this may not be the case, but if your pilot jets were doing their job, it may run good at lower rpm's, but when you open up the throttle and get the main jets going, it might be introducing too much fuel. A trick I used to do on the snowmobiles, was to find a straight strech, and bomb along full out, kill the ignition while keeping the throttle fully open until you came to a stop. Then you yank the plugs and check them, this was 'supposed' to show how the cylinder ran at full throttle. Then again, this method could be a load of crap.

    If you find the compression reading is very low or zero in one cylinder, it is highly probable that internal engine damage exists such as:

    The piston could have a broken connecting rod or a hole in it.
    A valve could be stuck or leaking.
    There could be a broken valve spring or a bent push rod.
    The camshaft has excessive wear and is not opening the valve(s).
    If the compression is low or zero on two adjacent cylinders, it would indicate:
    There is a 'blown' or weak sealing surface at the head to block mounting area, which basically means a bad head gasket.
    The camshaft is broken in an area that operates valves for two adjacent cylinders.
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  9. #8
    Thanks I'll pull the head today to check the Cylinder walls and valves. I started with the needles up 1 ring from the bottom so I have room to reduce the fuel from the Main jets. The pilot jets shouldn't have been effected by changing the main jets at least I didn't think they would be . Why would the air screw need to be opened another 1/4 turn. Idling at 2500 is where it would turn the pipes red and over heat.I Didn't change anything to effect this problem but now its fine. It will still spin the rear wheel and bring the front wheel off the ground in 1st gear and carry the front wheel in second so it turns on great from 6200 to 9000 rpm. It just doesn't want to wind higher in the upper gears . I have the velocity stacks on it now but the the air cleaner was clean when I started messing with it and the both the paper and gold colored metal fuel filters Where clean. I know I'm running to much fuel on the main jet but it isn't so far off just a needle ajustment could take care of is it?

  10. #9
    I didn't remove the Head because the exhaust cam had jumped 3 teeth. I don't have the specs to time the cams but the compression is #1 124 #2 125 #3 117 3#4 128 . Soon as I find the specs on timming them I'll put it back togather and try it.

  11. #10
    Registered User Array
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    Feb 2005
    1998 Ninja ZX-6
    Wow sounds like you've been thru alot with this bike. But definately those compressions sound better. Could be a bit higher, but at least they are more consistant now too. thats crazy how one cylinder was 53 and the other 102. The difference i hear is supposed to be within like 15% or so. One way to tell if the rings, or cylinder walls are loosing some compression is if the first turn-over brings the compression rating right up to the highest point, or if its substantially lower. If it does take a few cranks to get ur highest reading, could be worn rings or something. Good luck with everything.

  12. #11
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    Nov 2010
    1992 zx 600 c ninja

    ninja zx 600 , 11-2-2010

    i have a ninja zx 600 c that im having about the same problem with but my problem isn't that its not picking up in higher gears but just has no top end an will not rev over 6000rpms or if u try it will just cut out an i saw all the problems u had with your bike an all the responces u got just figure some one might have a better ideal of what my problem might be

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