spark unit burned

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spark unit burned

pacochopper
Hello to all, my nick is pacochopper

Sorry my english is very very very bad.

I write from Sevilla, España.

I am constructing a bike, cb 650:

-frame: yamaha xj 650 very modified.
-swingarm: chopped 11 cm.
-gas tank: sportster.
-front end: sportster.
-head light: bates 3".
-seat: metalflake gay jajaja.
-bar: yamaha sr 125.
-suspension: sportster low.
-front wheel: yamaha virago.
.....

The engine this one very good condition, but I have serious problem electrical.
The bike, she has been stopped 8 years, the engine has only 30000 km.

Once with everything mounted in the chassis, cleaned carburators, new battery....press start button and runnnn. The engine sound very well. But after a minute in march , the fuse of the solenoid breaks and one of the cdi (oki mps-200) burns, the silicona is melted and throws(adds) white smoke.

I buy two cdi to good price.

Since the electrical installation is the original one of the motorcycle, I think that it(she) can be damaged, make simplified
 
I install the new cdi to her, press start button and ruunnnn again. But after 1 minute, the engine stops , the fuse of the solenoid returns to be broken, I replace it, and again one of the cdi this one burned. I believe that I am going to cry.

Has this happened to someone?
For that it happens?

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The coils not screwed to the chassis, not ground to the frame. Only the wiring of the cdi.
If there is no ground of the chassis in the coils. Is it possible to burn the cdi?

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These are the spark unit burned:
oki-mps 200

The coils without ground, they were fixed by tape for the test on the road
 
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Searching the Internet there are more people with the same problem:


 79 CB750K CDI spark units/idling problem/Crash bars

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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

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Question
Ive got a 1982 honda cb750f supersport.  The bike has about 30,000 miles on it. I was riding  down the road the other day when my main fuse blew.  I looked for a possible problem, and when I didnt find one, I stuck a piece of wire where the fuse goes so I could get home. After I started my bike I smelled something burning.  One of the spark units had melted, but the other was fine.  I disconnected the burnt unit and drove home.  when i got home, i removed the burnt wire from the harness that goes fron the spark unit to the coils and to the run switch.  The wire was black with a white stripe and it was the only wire that had melted.  I ran new wire, replaced both spark units and replaced the run switch.  The bike ran fine for about 3 days then it melted one of the new spark units.  Ive searched for a shorted wire, but i didnt find any.  What could be causing this problem?  Thanks for your help


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Waiting for help
 
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Re: spark unit burned

shadow06
one thing to check is .your coil should not be a lower resistance than your ignition system or the coils will over heat and will burn out .you can use a coil of higher ristance .example  as a 5 ohm coil and a 1.5 ohm cdi system . the ohm ratings should be marked on the coils  not sure about the cdi units .you may need the manufacters info sheet . hope this helps
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Re: spark unit burned

pacochopper
Thanks men

the coils are original Honda CB 650
I think the problem is not having ground in the coils.

With your message, I confirm that the problem may be in the coils.
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Re: spark unit burned

shadow06
the ground circuit for the coils is controlled by the cdi unit .it makes and breaks the ground to induce the high voltage current to spark across the spark plug gap