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  1. #1

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    Hey, hoping someone can help



    my 79 cx500 has had an issue i've been trying to solve. starts well, runs well on the center stand, but when I ride it, it gets really sluggish and bogs down at 3500 rpms up until about 5000 rpms then regains some strength...but it takes forever to get from 3500 to 5000...



    long story short, i tried pulling the spark plug wires on each side as the engine was going sluggish...pulled the left and the bike almost died completely, plugged it back in and the felt the power return to the normal level of sluggishness. tried same thing with the right and there was basically no change. So that told me that the right side wasn't performing and was probably a bad coil. so i switched the coils (as well as the lead wire so as not to disrupt the firing sequence) and figured the problem would move to the left cylinder as it followed the bad coil. but, to my dismay it didn't...it still stayed on the right. So what is this telling me??? Do you think maybe its a CDI problem and the lead wire going to the right side coil isn't getting the proper pulse? Can anyone tell me what resistance or voltage measurements I should be looking for?



    I'm still very much a newbie at motorcycle mechanics, and electrical is probably my weakest side...so all help is appreciated!!
    79 Honda CX500 Deluxe

  2. #2
    Senior Member Justen's Avatar
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    http://globalcxglvtwins.forumlaunch....php?f=17&t=521







    Because it's the right side, did you check the right spark plug for color conditions? Could be something with the carb on that side.
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  3. #3

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    Quote Originally Posted by Justen View Post
    http://globalcxglvtwins.forumlaunch....php?f=17&t=521







    Because it's the right side, did you check the right spark plug for color conditions? Could be something with the carb on that side.


    thanks, but i've already done all these tests. all my measures are within spec



    1/5 = 114

    2/5 = 95

    3/5 = 210

    4/5 = 114

    6/5 = 95

    7/5 = 214

    8/9 = 87

    5/9 = 429



    also, i have replaced the plugs with brand new ones, and have swapped those from side to side with no differences.



    i can't imagine its a carb issue. mainly because the carbs were just cleaned and rebuilt by Larry Cargill over the winter and the bike hasn't been really ridden since putting them back on. plus, the bike is smooth and perfect from 1000rpm up to 3500, and from 5000rpm up. if it were a carb issue wouldn't i be having problems more broad than that?



    my battery is probably needs replacement. when its charged i get 12.4 V readings and over 14 when running at about 3000 rpms in neutral, but the battery seems to die easy while working on the bike so I am assuming it needs replacement. But could that cause such a specific issue as this?
    79 Honda CX500 Deluxe

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  5. #4
    Senior Member Shep's Avatar
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    What is the condition of the air-Dam/Spoiler heat deflector on to top of the engine?If missing or damaged then coils can over heat.



    Check the resistance of the coils as per,





    Click here,



    http://globalcxglvtwins.forumlaunch....php?f=10&t=335



    Check the fuel filler cap air vent and ream clean high pressure air blow through if need be.
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  6. #5

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    Quote Originally Posted by Shep View Post
    What is the condition of the air-Dam/Spoiler heat deflector on to top of the engine?If missing or damaged then coils can over heat.



    Check the resistance of the coils as per,





    Click here,



    http://globalcxglvtwins.forumlaunch....php?f=10&t=335



    Check the fuel filler cap air vent and ream clean high pressure air blow through if need be.




    thanks! i'm going to sound pretty dumb here, but as I said I'm a newbie, especially with electrical. I'm lost in this sentence



    "The good coil tested 7.5k approx between the LT wire and the HT wire.The decent plug cap had continuity as it should as my plug caps don't have Resistors in them."



    and as far as the air dam question, what does this look like? I don'e recall seeing anything around or under the coils attached to the frame, but i can go re-look if i know what i am looking for
    79 Honda CX500 Deluxe

  7. #6
    Senior Member Shep's Avatar
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    Part number 9 on here,



    http://www.cmsnl.com/honda-cx500a-19...5.html#results



    Also are BOTH coils reading 7.5k?
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  8. #7
    Senior Member RVP3's Avatar
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    Check out Shep's post about testing coils here: My link



    And check out Larry's post about plug caps and resistors here: My link
    1981 GL500I

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  9. #8

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    Quote Originally Posted by Shep View Post
    Part number 9 on here,



    http://www.cmsnl.com/honda-cx500a-19...5.html#results



    Also are BOTH coils reading 7.5k?




    gotcha. i will remove the tank tonight or tomorrow and look for this part and its condition as well as check the resistance of both coils, and then post my findings
    79 Honda CX500 Deluxe

  10. #9

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    ok, so bike is still having same issue...loss of power on right cylinder from 3500 through 5000 rpms (roughly).



    i have a brand new battery on the bike now



    checked both coils, both read over 7.5k resistance. i have swapped the coils to each side, have also swapped the plugs to each side. no change, problem still stays on the right.



    all resistance checks of the stater coils and everything check out as mentioned in previous post



    i'm open to suggestions that this may be a carb issue, but as mentioned, these carbs were just cleaned and rebuilt by larry, and there are no other symptoms of any carb problems. bike starts and idles great. responds really well to throttle when in neutral on the stand. i would think if the right carb was getting starved of fuel i'd have issues with idle and throttle in neutral, no??



    what can i do to look at the cdi? could it be an issue with the lead going from the cdi to the ignition coil not getting the right pulse or something?
    79 Honda CX500 Deluxe

  11. #10
    Senior Member Justen's Avatar
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    jware21



    I would look at the carbs again. Just because Larry fix them doesn't mean there is no issue. The second you plug those carbs into the gas tank. You could have sucked in rust or dirt in the carbs. I would pull the carbs, check the bowl conditions. Check the jets. If there is signs of crud, I would empty the gas tank and try to get it cleaned out good. I would also pull the petcock and clean the screen. Replace the fuel filter and blow the gas line clean with the air compressor, or replace the line.



    Also another thing to keep in mind. Testing a coil with a multimeter is a good starting base. But doesn't rule out a bad coil. Coils can fail when hot, they short out. Cold, they are a perfectly good coil. Only bench testing them for a period you can catch it starting to fail. As you said, you swapped coils and no change. This is another good way to test a failing coil. Something to keep in mind dealing with coils.



    Usually on the cx bike it's three things that can cause one side to fail. coil, cdi, and, carb. After that I start looking at pulsars and wiring. On other honda's, I've also had it where a valve collapsed, causing the one side not to work. But this condition was hot or cold and wasn't mistakable. You can hear it's different.



    Couple other things you can try. Test the cdi output, (best tested after a ride and cdi is warm). Test the inputs to the cdi. You can test the cdi box it's self if you have a oscilloscope, otherwise swap the old box with another and see if you still have firing issues.



    http://www.youtube.com/watch?v=Q6kHbyUibvg
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