2001 ZX6R- Misfire upto 4K- Help required



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Thread: 2001 ZX6R- Misfire upto 4K- Help required

  1. #1

    2001 ZX6R- Misfire upto 4K- Help required

    Bike: 2001 ZX6R ~35000KM
    Maintenance done within last year by PO:
    Plugs, air filter, fuel filter, valve adjustment, carb cleanand sync, new float bowl orings, new float valve, float adjustment, battery approx.2 years old, carb is jetted but unsure of exact #s without pulling it
    Issue: Stumble, misfire at idle. Misfire until about 4K RPM.After that range bike runs fine.

    Description: Bike was running fine until about 1 week ago,maybe a little bit rich (sniff test).
    Out of the blue, began stumbling and misfiring at idle andup to about 4K rpm.

    Pulled tank and airbox to inspect. Noticed some black goop(somewhat consistent to oil) near #2 coil. Cleaned it up. Didnít noticeanything obviously disconnected or torn vac lines. Pulled plugs and they lookedokay. Surprisingly not wet. Put everything back together and started up.

    At this point, bike was again running rough. Touching throttle would send revs down. Let it warm up and turned it off.

    Came back to it a couple hours later and this time it firedup (no bogging but still stumbling). Took for a quick spin around the block(still missing under 4K). Sprayed brake cleaner on headers and it evaporated onall 4.
    Gas in tank is about 2 weeks old- Shell 91.

    Not sure where to start looking with this issue so all help is appreciated.

    Thank you in advance

  2. #2

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    Re: 2001 ZX6R- Misfire upto 4K- Help required

    So more air = lower rpms? That should mean you are lean. My guess is a plugged idle jet. Once you get onto the main jets enough your problem goes away.

  3. #3
    boyoboy's Avatar
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    Re: 2001 ZX6R- Misfire upto 4K- Help required

    Are you comfortable removing and working on the carbs? you stated carbs cleaned and jetted previously. My thoughts would be to take a look at the carb internals, and determine what jets are in the carbs and compare to oem specs. Im guessing the bike has a pipe and the pilot jets have been replaced with a set of pilots that are too rich. Take a look and compare, you may want to go one size smaller on the pilots if its running poorly from 0-4000rpms.

    Even if this isn't the case, at least you will know the jetting specs.
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  4. #4

    Re: 2001 ZX6R- Misfire upto 4K- Help required

    Quote Originally Posted by GreyGhost View Post
    So more air = lower rpms? That should mean you are lean. My guess is a plugged idle jet. Once you get onto the main jets enough your problem goes away.
    Thank you for the reply.

    Out of curiosity, what would cause a plugged jet out of the blue?

  5. #5

    Re: 2001 ZX6R- Misfire upto 4K- Help required

    Quote Originally Posted by boyoboy View Post
    Are you comfortable removing and working on the carbs? you stated carbs cleaned and jetted previously. My thoughts would be to take a look at the carb internals, and determine what jets are in the carbs and compare to oem specs. Im guessing the bike has a pipe and the pilot jets have been replaced with a set of pilots that are too rich. Take a look and compare, you may want to go one size smaller on the pilots if its running poorly from 0-4000rpms

    Even if this isn't the case, at least you will know the jetting specs.
    Thank you for the reply.

    Yes there is a pipe on it.

    I am comfortable with pulling the carbs. Just not sure what to look for when I do lol.

  6. #6

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    Re: 2001 ZX6R- Misfire upto 4K- Help required

    Quote Originally Posted by 01zx6r View Post
    Thank you for the reply.

    Out of curiosity, what would cause a plugged jet out of the blue?
    Rust or other contaminants in tank or fuel normally. Many bikes don't have a great fuel filter. The idle circuits have smaller passages than the main circuits so they are more likely to be plugged.

    A small vac leak could also cause the same symptoms. Hitting a hard bump could have dislodged something or opened up a crack in a rubber part. Once you get the revs up, the amount of air leaking becomes inconsequentially small.

    How many km do you have on the current tank of fuel? Before going nuts with disassembly, it may be worth a shot to syphon off most of the existing fuel and refill with new gas. Contaminated gas is not likely, but it is possible. Put some of the gas that came out in a clear container and check for junk. If it looks good, dump it in your car.

  7. #7

    Re: 2001 ZX6R- Misfire upto 4K- Help required

    Quote Originally Posted by GreyGhost View Post
    Rust or other contaminants in tank or fuel normally. Many bikes don't have a great fuel filter. The idle circuits have smaller passages than the main circuits so they are more likely to be plugged.

    A small vac leak could also cause the same symptoms. Hitting a hard bump could have dislodged something or opened up a crack in a rubber part. Once you get the revs up, the amount of air leaking becomes inconsequentially small.

    How many km do you have on the current tank of fuel? Before going nuts with disassembly, it may be worth a shot to syphon off most of the existing fuel and refill with new gas. Contaminated gas is not likely, but it is possible. Put some of the gas that came out in a clear container and check for junk. If it looks good, dump it in your car.

    So over the weekend:

    Check for vac leaks. None found

    Pulled carbs. Clean as a whistle inside. Floats and needles not sticking.

    Main jet sizes: Cylinder 1 and 4 : 155
    Cylinder 2 and 3: 157.5
    I believe these are factory sizes.


    Pilot jet sizes: Mikuni jet stamped 15 on all four.
    I think these are not from the factory. Maybe one size bigger if I am reading the charts correctly.

    Now I am stuck. Should I start playing with the mixture screws. The caps have been drilled out so someone has been in here.

  8. #8

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    Re: 2001 ZX6R- Misfire upto 4K- Help required

    Quote Originally Posted by 01zx6r View Post
    So over the weekend:

    Check for vac leaks. None found

    Pulled carbs. Clean as a whistle inside. Floats and needles not sticking.

    Main jet sizes: Cylinder 1 and 4 : 155
    Cylinder 2 and 3: 157.5
    I believe these are factory sizes.


    Pilot jet sizes: Mikuni jet stamped 15 on all four.
    I think these are not from the factory. Maybe one size bigger if I am reading the charts correctly.

    Now I am stuck. Should I start playing with the mixture screws. The caps have been drilled out so someone has been in here.
    Did you blast carb cleaner through the jets while everything was apart?

  9. #9

    Re: 2001 ZX6R- Misfire upto 4K- Help required

    Quote Originally Posted by GreyGhost View Post
    Did you blast carb cleaner through the jets while everything was apart?
    Yup through and through

  10. #10

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    Re: 2001 ZX6R- Misfire upto 4K- Help required

    Check your wiring harness connections for corrosion. On a bike this age, I'd open each connection, spray it with contact cleaner (fine wire brush anything that has white or green chalky corrosion), then apply a small amount of dielectric grease to the connections before reconnecting.

    Intermittent electrical connections in harnesses often cause problems like this. They are difficult to diagnose and often lead to replacing other parts that are working fine.

    The fact that you're getting good power above 4000rpm is is consistent connection issues and might be a clue that this is a problem. Your charging system should be peaking at 4Krpm, providing enough power to excite intermittent connections.
    Last edited by Mad Mike; 09-21-2017 at 04:45 AM.

  11. #11
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    Re: 2001 ZX6R- Misfire upto 4K- Help required

    try turning in your mixture screws until lighted seated, make a detailed note on number of turns req'd - and record for each carb. This will allow you to put them back where you started from in the event things dont improve.

    these mixture screws should probably be about 2.5 turns out from lightly seated. You can try adjusting each of the mixture screws to where you get the highest idle revs. then reset your idle revs screw to get stock idle (1000-1200rpm?) and test ride.

    never bottom out the mixture screws more than lightly seated as this could damage them.

    "Like" mikes suggestion to clean your electrical connections and grounds. Always a good idea for a mature bike ...

    Do you have a slip on or full pipe? did you measure float level of the carbs? float levels can have a large effect on jetting. check that you have carbs perfectly sealed with no air leaks at clamps. rubbers not leaking or torn.

    You can also bench test the carbs for balance. You can visually look to see that they all have - even to each other openings.

    Is the up to 4000rpm misfire/stumble worse with cold engine? or hot engine? or the same regardless if engine is cold or hot?

    EDIT
    After re-reading post #1. "bike was running fine before and just started suddenly running bad at idle and up to 4k" makes me think this problem isn't the carbs or jetting. nothing had been changed with the carbs. I would do as mad mike said and very carefully go through all your electrical connections and clean. including grounds to engine or frame. take your time to make sure they are all VERY clean and corrosion free. check near connectors to see if the copper wire itself isn't green/black and rotting..
    Last edited by boyoboy; 09-21-2017 at 11:41 AM.
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