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  1. #1
    1980CX500CUSTOM's Avatar
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    Feb 2012
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    Walla Walla, Washington
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    59
    i have a 1980 cx500 custom. i think the battery is bad as it doesn't hold charge overnight. i have low compression on the left cylinder, it has been that way since i bought it. the left coil was also not getting a spark signal from the cdi. I recently bought a 79cx500 standard parts bike and robbed the cdi box off of it. Now i am getting spark on both cylinders. I was not sure what had been done to the carbs, so i ran the pilot screw for the mixture all the way in and then out 2 full turns. I started the bike and let it warm up. to check the spark i unplugged one coil at a time at the bullet connector coming out of the cdi box. when i unplugged the coil for the left cylinder it made little to no difference, but when i unplugged the right coil the bike almost died. Also, during this warm up the bike's idle was betweeen 3500 rpm and 4000 rpm. So i took the bike for a ride (this is where the turbo kicks in) and at 5k rpm it starts to sputter and hesitate and then around 6500 or 7k rpm the bike takes off!!! This is like a turbo kicking in, and so i kinda peed my pants a little, then grinned from ear to ear, shift up and kept the throttle pegged. While this is a very "fun" ride, i am still wondering what is wrong with my bike....any help would be appreciated. I have a ignitech on it's way but i would like to have all the other issues resolved so when it arrives so i can plug and play....
    1980 CX500 CUSTOM.

    "Be kinder than necessary, for you never know the battle that others are fighting˝

  2. #2
    1980CX500CUSTOM's Avatar
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    Feb 2012
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    Walla Walla, Washington
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    Quick update, i do not have a hg meter to balance the carbs. what i do have is a hand vacuum gauge for bleeding brakes. This meter measures in pounds. I unscrewed the phillips head screw on the intake pipe into the head and hooked up my vacuum guage. the needle jumps between 16 pounds and 12 pounds on the left carb. On the right carb it jumps between 6 and 3 pounds. I downloaded the high res manual for the cx500 off the wikispaces site and looked up section 3-7 and according to the picture on the bottom of the page there is a adjusting screw with a lock nut on it to adjust the vacuum on the right carb. So, i wandere3d out to my bike and looked, and looked, then i took opff the tank and looked again. no adjusting screw!!! i looked all over and still i found nothing. i checked the id numbers on the carbs and found 25acsj1 on both carbs imprinted on the left side body of each carb... Does anyone know what this is and how i can adjust the vacuum without a adjusting screw....?
    1980 CX500 CUSTOM.

    "Be kinder than necessary, for you never know the battle that others are fighting˝

  3. #3
    Supreme Ognosticator jjwelderman's Avatar
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    Dec 2010
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    I'm interested it this as well so I'll be watching.
    I live out in the country, ya know."



    1980 Honda CX-500 Custom

    1985 Kawasaki 454 LTD

    South Central Texas

  4. #4
    Senior Member Allan's Avatar
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    Aug 2010
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    3,953
    Try checking the resistors in the spark plug caps, here is a link.
    ...and as the elders of our time choose to remain blind, let us rejoice and let us sing and dance and ring in the new. Hail Atlantis!

    1975 XL-100, 1978 CX500, 1980 CX500, 1981 CX500

  5. #5
    Senior Member Blue Fox's Avatar
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    Aug 2010
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    I'm fairly sure there is a adjusting screw for the balancing. It will be closer to the left carb, on the linkage. It may still have a drop of yellow locking paint on the screw to. It is a flat headed screw with a 8 mm locking nut on the outside.



    I think you may be in for a lot of frustration using a pound type vacuum gauge, but it may be better than nothing. There are several posts on how to build your own nanometer on this forum, including in the Wiki. If you only have one gauge, you will be constantly shifting the gauge from one cylinder to the other and blocking the one not in use.



    To lessen the bouncing on the gauge, you need to put restrictions in the hoses close to the intakes. These can be an aquarium air shutoff, or I have used a needle nosed Vise Grip. Just clamp the Vise Grip on the hose loosely, then tighten the adjusting knob until the bouncing stops.
    1983 GL650I, 1980 CX500, 1979 CX500, 1982 GL500I, 1978 CB550, 1974 CB350F, 1973 CT90

    Need information? Try our new Wiki site: http://cxgl.wikispaces.com/

  6. #6
    Senior Member Reg in Bristol's Avatar
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    One possibility is a sticky carb piston

    that isnt lifting properly at lower engine speeds

    When eventually, the airflow is enough to lift it

    you get the 'turbo' effect



    Mis set Carb balance has its effect but this doesnt usually

    stop it picking up in such a pronounced way.



    It may well be other things of course, first thing I'd do is inspect the plugs

    then systematically check the rest of the fuel and ignition system
    I started to resurrect my site at
    http://tinkrin.netau.net/index.html
    but TBH, cant be arsed

  7. #7
    1980CX500CUSTOM's Avatar
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    reg, bkue fox, and allen... thanks for the input. I will be using my meter and checking the cdi to make sure everything is i spec. I will look again for the adjusting screw and see if i can find it. the right carb should be the one that is adjustable right? I have read the post on building your own nanometer and plan on getting the supplies to do so tomorrow. As far as the spark plugs, they are brand new and gapped properly. I am looking into also rebuilding the resistor caps as i just saw that build up last night. Thanks again for the wealth of knowledge and expertise guys, i really appreciate it!
    1980 CX500 CUSTOM.

    "Be kinder than necessary, for you never know the battle that others are fighting˝

  8. #8
    Senior Member stern-69's Avatar
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    Agree with Reg, the piston may be sticky. If you like the "turbo kick-in" then I would suggest you clean the carbs REALLY good and ballance them. Ballancing makes a huge difference to the bikes performance, but only if the carbs are spotless. May seem like a pain but its the single most important thing you can do to the bike to make it run well

  9. #9
    Senior Member Reg in Bristol's Avatar
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    testin the piston is often as simple as stickin yer finger in the back

    lifting each piston fully and letting it drop.

    They should both feel the same and lift with little resistance then drop freely

    I've had some where the piston looked fine but when the cap was fitted, got sticky

    so I always test before fitting to the bike

    Remember:

    when removing carbs, start from the manifold and work back

    slacken hose clips, remove manifold bolts,pull carbs back a bit, twist manifolds and remove

    then work the carbs forward out of the rubbers and remove to the left

    then its easy to remove the cables if you wish.

    Apart from the hose clips theres no need to disturb the airbox rubbers

    just push the clips back on the rubbers so they dont get lost or forgotten when

    re-fitting the carbs
    I started to resurrect my site at
    http://tinkrin.netau.net/index.html
    but TBH, cant be arsed

  10. #10
    Eddie42's Avatar
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    Quote Originally Posted by CX500CUSTOM View Post
    the needle jumps between 16 pounds and 12 pounds on the left carb. On the right carb it jumps between 6 and 3 pounds.


    A perfectly evacuated vacuum at sea level (Close enough for Walla Walla) is 14.7PSI. And you've got some air and gas in there for sure.



    -Your forum Physicist



    I just had my carbs in my hand this weekend. There is a small phillips head set screw, and spring in a brass bracket near the throttle linkage and choke linkage. Mine had some locktite on it, and I also didn't touch it, but that is the Carb balance.
    79 CX500 Custom

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