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newbie needs help

This is a discussion on newbie needs help within the Technical forums, part of the Caferacer.net Forums category; Hi all. been watching the forum for awhile and you guys seem very knowledgeable about these old cb's so I decided to join.I bought a ...

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  1. #1
    Member cappys's Avatar
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    newbie needs help

    Hi all. been watching the forum for awhile and you guys seem very knowledgeable about these old cb's so I decided to join.I bought a 72 cb450 a few weeks ago. a little bit of work and I had it running good.
    ,breaks,cleaned petcock,spark plugs. that's all I had to do.Drove it around for about 20 mins.It was parked for 2 days when I went back to it I couldn't get it to start. did some checking and I have no spark in one cylinder.I changed the spark plug and still no spark.I'm guessing points/coil/condensor but I don't know where to start. Any help is much appreciated.
    Shawn

  2. #2
    Administrator borzwazie's Avatar
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    man, that thing is gorgeous. where'd you find it?

    As for spark, I'd check the coil(s) - you can measure the impedance of the coil if you have the right tool - if it's off, the coil is bad. They're not that expensive, and you can probably replace the pair of them with coils of the proper impedance from any auto parts store. You can't replace just the wires on the stock coils, and if they're original a break in the wires is likely.
    "This site is bullshit."

  3. #3
    Member cappys's Avatar
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    Thanks for the compliments .The story is that the bike sat in the window of a motorcycle shop (advertisement) for 15 years or better it only has 8000 miles on it.
    somewhere in N.C. Also thanks for the info if coils are reasonably priced I'll just go ahead and change them.They probably are stock.Any idea on what the proper impedance should be?
    Shawn

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  5. #4
    Senior Member bmartin's Avatar
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    Dido on the bike - nice looking. Re-check your points settings - it doesn't make any sense why it runs on day and dies after sitting for a few days.
    Bob - Palmyra NY
    2 - 69 CB750, 1 Turbo
    1 - 71 CB750

  6. #5
    Member cappys's Avatar
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    thanks. I don't have any feeler gauges yet so I'm not sure of the points settings. but I did take the cover off of the points and turned the motor over. and I did see spark on both sides. I will recheck when I get a gauge.
    Shawn

  7. #6
    Senior Member krapfever's Avatar
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    Check that the plug wire cap on the dead cylinder is fully screwed into the wire.

    Nice bike.


  8. #7
    Member cappys's Avatar
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    ok so I check my points their ok and then I checked the plug wires looked good no cuts or breaks not even dried out checked the plug to wire connection looks good.
    so I started looking for coils. Local honda shop can't get em. ok Ebay.Found a set on ebay and the same guy was selling raask rear sets and a bubble seat for a cb450.
    Emailed him struck a deal. Now I have a set of coils on their way hope that fixes the spark problem.can't wait to caffeinate my bike.
    Shawn

  9. #8
    Senior Member kenessex's Avatar
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    Shawn,
    Did you charge the battery? Those Hondas have to have 12V to run. That is 12V under load. Stick a volt meter on the battery and turn the ignition on and see what you have. I doubt you coils went bad just sitting. Lots of people replace good coils but don't know it because when they unplugged the old ones and plugged the connections in for the new ones they cured the bad wiring connection that was the original cause of the problem.

    Ken
    WERA 119
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    AHRMA not anymore
    \"Think twice before you speak, and then you may be able to say something more insulting than if you spoke right out at once.\"
    Evan Esar
    Newbies, Geeto and Tex (Bye Tex)hate me!!

  10. #9
    Senior Member Geeto67's Avatar
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    step 1: check battery - you need some voltage to be able to polarize the magnets in the stator, otherwise she don't run

    step 2: check points, if there is a short in the igniton (or you accidently left it on) and one of the points was closed then it goes bad quick.

    Step 3: check plug wires. These bikes are old, and honda plug wires can't be changed without changing the coil. Make sure your plug wires are making good contact.

    Step 4: check connections to coil. Sometimes a loose or corroded wire will kill the whole deal.
    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

  11. #10
    Member cappys's Avatar
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    battery is 2 weeks old and has been hooked up to a trickle charger after each attempted starting session.will definitely check the wiring to the coil.Don't know why I didn't think of that. Thanks Ken
    Shawn

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