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  1. #1
    Newbie
    My Bike(s)
    1979 Honda CB750K
    Location
    Pittsburgh area, PA
    Posts
    3

    Exclamation 79 CB750K CDI spark units/idling problem/Crash bars

    Hey,

    I posted this on the maintenance forum, but I figured I would give it a try over here too.

    I just ordered off eBay a working set of CDI ignition spark units for a CB750K.

    Last week my Dad took the bike for a ride and came back and the bike was smoking under the seat. He shut the key off, I had some water that I poured on the spark unit to put the flame out, and the spark unit was basically fried. I noticed that one of the battery cables was lose, but it never hit the frame. Also, my units are the ones that have the tar on the back of them, so that is actually what was burning.

    I was speaking to the gentleman I bought the spark units off of, and he said those units require a solid 12 volts to them. He said I should check the resistance to the ignition coils before hooking up the spark units and trying to get the bike running again.

    How should I check the coils?
    Is there anything specific I should test with a voltmeter?
    If so...what leads should I connect the meter up to?

    Once I get the bike running, I am going to hook a voltmeter up to the battery to make sure I am getting a good 12 volts charge, the alternator may be giving up too.



    Second question, on a cold start up the bike is kind of cold blooded, but if you hold the throttle for about 3 minutes at 2000-3000 rpm, I can let go and the idle will rest and run at 1000 rpm which is where it is spose to be. If you ride the bike for about 5 minutes up and down the road, the bike will then idle around 3000 rpm and absolutely will not come down. If you reach under the tank and pull on the throtlle cable it idles, but as soon as you let go it goes right back to 3000 rpm. I put a good oil on the upper part of the cables figuring maybe it was just getting stuck, but it still isn't working right.

    What else could cause this before I spend $150 for a mechanic to look at it?



    Third and final question...What crash bars fit a 79 Honda CB750K?


    This motorcycle thing is all new to me so I need all the help I can get. Cars I am fine with, bikes I have alot to learn.


    Thanks!

    -Dave


    2001 Chevrolet Blazer 4WD
    1986 Oldmobile Cutlass
    1980 Chevrolet Malibu
    1967 Chevrolet Camaro RS/SS (a real one)
    1979 Honda CB750K

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  3. #2
    Newbie
    My Bike(s)
    1979 Honda CB750K
    Location
    Port Orchard, WA
    Posts
    1
    My CB750K had no power to go uphill until I replaced the CDI units and the coils. The CDI units were like yours, fried! and after checking the spark plugs I found that the number 1 and 4 were black indicating no spark and the 2 and 3 plugs were a nice gray indicating normal ignition spark. I suggest you check the plugs for condition and if black due to the non spark problem replace the coils. I found NEW after market coils for about $45 each which is a lot less than Honda wants to bleed you for them. After replacing the CDI units and coils the bike goes up hills like a shot! Also the bike wouldn't idle well at anything less than 2 to 3 grand and now idles at 1k or so and is smooth. My mileage went from 28-35 mpg to 50 mpg. Huge improvement all around. Good luck with your CB750 and by the way highway / crash bars are very hard to find for a 79 CB750K. Watch e-bay for used ones as I've never found new ones and I'm still looking.

    bink1595

  4. #3
    M-J Lifetime Achievement Award
    My Bike(s)
    1980 Yamaha XS850 - being dismantled; 1999 Kawaski Concours
    Location
    Washington County, WI
    Posts
    13,275
    I found NEW after market coils for about $45 each which is a lot less than Honda wants to bleed you for them.
    I strongly agree - never, I mean never, buy anything out of the boneyard that is involved in the ignition system.

    Mother nature does a real number on anything electrical - vs somewhere where new aftermarket is being produced.
    Couldn't put "fail" across Lolo's picture, but she did come in 4th in the 100 m hurdles - still one heck of an effort.


 

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