78 cb550k 605cc bore misfire... - Page 3
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78 cb550k 605cc bore misfire...

This is a discussion on 78 cb550k 605cc bore misfire... within the Technical forums, part of the Caferacer.net Forums category; while it is off the road check the coil leads, I get the feeling you have a loose connection somewhere....

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  1. #21
    Senior Member Geeto67's Avatar
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    while it is off the road check the coil leads, I get the feeling you have a loose connection somewhere.
    Ever tried. Ever failed. No matter. Try Again. Fail again. Fail better.
    - Samuel Beckett
    A tool is just an opportunity with a handle
    - Kevin Kelly

  2. #22
    Senior Member Teazer's Avatar
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    So it's OK until you ease off at highish speed/load and after that it stutters and won't run. It doesn't break up before you ease off form speed though, just after you start to decelerate?

    Could be that coil lead of Geeto's or the carbs sucking something in under situation with high gas velocity/high vacuum conditions.

    My guess would be water or small debris in the float chambers being sucked in with high vacuum and dropping back out after it sits for a while. Sounds odd, but that's how I understood your explanation of the circumstances.

  3. #23
    Member photoputz83's Avatar
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    i took the carbs completely apart and they were clean as a whistle. i decided to clean them out again anyway and replaced the o-rings and bowl gaskets. hell i had them on hand so i figured why not. i made sure that i cleaned out all of the passage ways between the carbs and anywhere else that debris could be settling. put them back together and they will go back on tomorrow. i will also take a peek at those leads. i have to work in four hours and have not slept yet so i guess now is the time.

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  5. #24
    Member photoputz83's Avatar
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    going to drain the tank and re-install the carbs then sync in a little bit. the mains and slows were clean and open. it did however turn the cleaning solution a bit cloudy but i doubt that it would have made that big of difference. we shall see. not much else i can do besides check the valves and adjust to spec for the setup. i did this when i ran the motor for the first time only 300 or so miles ago. i am pretty sure it isnt the problem. also i did a compression test lastnight and the results were as follows. cyl#1 (163) cyl#2 (160) cyl#3 (165) cyl#4 (163).....pretty consistant. this is the second time i performed a compression test with this kind of result.

  6. #25
    Senior Member jaguar's Avatar
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    Do you have the correct resistor installed to run those 3 ohm coils?
    Stock was 5ohms right? The same as a cb750?


    Basically you have added a ton of variables to the bike so it's hard to jump around to solve things.
    Really need to sit still and run though the systems..
    Also just because it's a new part makes no difference to it working or not. and you can't just assume it's installed the right way.
    I am Derby\'s Bitch


    Some times things come around that are so singularly inept it gives you a whole new appreciation for the ept

  7. #26
    Member photoputz83's Avatar
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    im ipc whma a-620a certified in wire harness manufacturing and electrical assemblies so yes i did my research, found all the correct wire schematics for this setup. everything was done right with the guidance of a seasoned cafe builder out of studio city, ca. and this setup with stock coils did the same thing so i can eliminate that possibility.
    quote:Originally posted by jaguar

    Do you have the correct resistor installed to run those 3 ohm coils?
    Stock was 5ohms right? The same as a cb750?


    Basically you have added a ton of variables to the bike so it's hard to jump around to solve things.
    Really need to sit still and run though the systems..
    Also just because it's a new part makes no difference to it working or not. and you can't just assume it's installed the right way.

  8. #27
    Senior Member Geeto67's Avatar
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    Remember, we are having to guess at your mods and skill level since you provided neither.


    Seasoned cafe racer builder <------- there is your problem right there.

    Have you checked for things shifting while you ride? I had a coil once that tried to weld my fuel tank to my frame because of a loose bracket. Only happened when braking, and it weirded me out why I would drop a cylinder on deceleration. Maybe something is loose somewhere and shorting out.

    We are trying to help, honest.
    Ever tried. Ever failed. No matter. Try Again. Fail again. Fail better.
    - Samuel Beckett
    A tool is just an opportunity with a handle
    - Kevin Kelly

  9. #28
    Member photoputz83's Avatar
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    when i say seasoned i mean 15 plus years and has modded cb750s for the last 10 to 12. numerous 836 big bore kits and such. not to mention the fact that he is from essex. so across the pond. i ended up dropping in a new rectifier and it was the key. the only thing electrically that i didnt replace. runs fine from idle to 12k. also upped the octane a bit with a new mix ratio of 30:70 turbo blue, 93 octane no ethanol.

  10. #29
    Member photoputz83's Avatar
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    and sorry about the lack of detail. pretty new with the forum thing. ill be a bit more in depth if i need help again.

  11. #30
    Senior Member jaguar's Avatar
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    always find it funny when guys from england that talk about the honda cafe thing....ace closed before the 750 came out right?....sorry thats just a pet beeve with me.

    so back to your bike.....didnt really answer many of the questions posed buy people trying to help.
    an answer of "it cant be that because its new" or "its not that because a master did it" is not helping anything.

    and really for the life of me i cant figure out what your "issue" is because you keep popping back and forth with the old and new motor.....or maybe im just drinking to much....



    What resistors did you install for the coils and how did you install them? this IS a difference...

    also dont just look for one component thats wrong broken or just messed up....since there are so many variables that you added its hard

    Please write up what ALL the mods and settings are and then talk about the symptoms are again
    I am Derby\'s Bitch


    Some times things come around that are so singularly inept it gives you a whole new appreciation for the ept

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