Author Topic: do CB900 coils bolt right on the 750k2 or do they need massaging first?  (Read 6480 times)

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amattel

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do CB900 coils bolt right on the 750k2 or do they need massaging first?

It looks like we almost got this into a faq but it never seemed to have made it.

this would be handy to have as a reference for future ignition system tinkerers.

Thanks,

Adam


Offline puppytrax

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It's not for a 750, but maybe this thread could be tied in, too (for us Little Four owners)...

1981 CB900 ignition coils on a 1976 CB550

http://www.sohc4.us/forums/index.php?topic=9248.0
...stock 1972 CB500 '500 Four' undergoing re-assembly...
...Stock 1972 CL450 'Scrambler' also being re-assembled...

Offline cben750f0

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mate i tried those coils on my F1 and the threaded caps that the leads screw to the coils with, hit the inside of the tank when you try and fit it.... could i suggest VF750/1000 coils on a modified mount, the exit downwards, and the you dont have to worry about them interfering with the tank....
you are never to old, to act like a kid... be safe
funny thing,chasing someone down hill on a bike 30 years older than theirs..
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Offline cben750f0

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a veiw from the bottom..peace
you are never to old, to act like a kid... be safe
funny thing,chasing someone down hill on a bike 30 years older than theirs..
he said \\\\\\\'it was like watching a 250kg unguided weapon getting stuck up you bum\\\\\\\ http://www.bikepics.com/members/trixtrem/

amattel

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My cb900 coils just arrived.

THey look different than the ones that you have CBEN

mate i tried those coils on my F1 and the threaded caps that the leads screw to the coils with, hit the inside of the tank when you try and fit it.... could i suggest VF750/1000 coils on a modified mount, the exit downwards, and the you dont have to worry about them interfering with the tank....

With mine the plug wires come from the front and the input wires are in the back.

I just checked them with the multimeter and they are both showing 2.5 ohms.






Offline cben750f0

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they are the 900 ones, the ones in the pics are the VF750/1000 coils... sorry if i wasnt clear, i found the 900 coils hit the inside of the tank on my F1,when installed... thats why i have gon the VF coils...
let me know if you need any help...peace
you are never to old, to act like a kid... be safe
funny thing,chasing someone down hill on a bike 30 years older than theirs..
he said \\\\\\\'it was like watching a 250kg unguided weapon getting stuck up you bum\\\\\\\ http://www.bikepics.com/members/trixtrem/

Offline SteveD CB500F

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Adam - let us know how it goes.

I'm happy to convert this thread into a FAQ once we get to the bottom of what fits and what doesn't
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1971 CB500K0 (US Model)

Offline dusterdude

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those mounts look a lot like the 750 mounts i had on my bike.when i installed my yamaha? coils,i couldnt use the 750 mounting pieces.all i did was wrap some cardboard around the 2 frame tubes under the tank and tie wrap the coils to the cardboard.they been that way for a little over a year and everything is working out fine
mark
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Offline cben750f0

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i agree you cant use the CB mount, as it is too narrow, and you cant us the 900 mount b/c its too wide, i tried both, and as i have mentioned b4 it interfers with the channel in the tank, thats why i used the VF coils, same basic coil, just exits out the bottom..
you are never to old, to act like a kid... be safe
funny thing,chasing someone down hill on a bike 30 years older than theirs..
he said \\\\\\\'it was like watching a 250kg unguided weapon getting stuck up you bum\\\\\\\ http://www.bikepics.com/members/trixtrem/

Offline Terry in Australia

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I've got a set of honda V4 coils like yours Ben, but javen't used them yet, how do they compare to Dynas? Cheers, Terry. ;D
I was feeling sorry for myself because I couldn't afford new bike boots, until I met a man with no legs.

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amattel

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ok.  I just tore into it...

And I can verify the the cb900 bracket is too wide (doesn't fit in tank channel) and the stock mount is too narrow to fit cb900 coils (tried it  ;D)

What I did get to work is to flip the coils in thier mounts so the plug wires are exiting backward.
This fits in the tank groove, just need longer plug wires.

My next step is to buy 8 feet of plug wire that I can cut to fit.

I was so pissed off as I went out to Kragen autoparts and they don't even carry ignition wire by the foot  >:(

Couldn't fins any in berkeley before closing time was upon me 6pm so despite my best effort will need to finish this after work tomorrow.

I don't see any other way fro these coils to fit except backwards.  Would be nice is someone could verify this is the common way to do this mod.

Is there any issue with plug wires passing close to head? I assume it is meant to withstand high temperatures.

thanks for the help,

Adam


amattel

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I couldn't find the copper core wire anywhere out here.

I found a universal silicone wireset.  Unfortunately they have about 5k ohm resistance and so do the caps!

It is running great, despite this.  Took it around the block and it just roars!

Here's somes pics on how I mounted it.  It fits perfect with the wires exiting toward the rear.

I still don't know how anyone else has done it but here's my solution.

Adam

Offline cben750f0

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the coiuls are great, just dont great grabbed by them when checking spark.... will start the heart thats for sure.. ;D..peace
you are never to old, to act like a kid... be safe
funny thing,chasing someone down hill on a bike 30 years older than theirs..
he said \\\\\\\'it was like watching a 250kg unguided weapon getting stuck up you bum\\\\\\\ http://www.bikepics.com/members/trixtrem/

Offline puppytrax

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My cb900 coils just arrived.

I just checked them with the multimeter and they are both showing 2.5 ohms.

I am curious as to which leads you used to get the 2.5 ohm reading...could you describe, please? Thank you!  :)
...stock 1972 CB500 '500 Four' undergoing re-assembly...
...Stock 1972 CL450 'Scrambler' also being re-assembled...

amattel

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each coil has 2 input leads and two output leads (plug wires).

I measured the two input leads. and got 2.5 ohms of resistance.


Adam

Offline puppytrax

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each coil has 2 input leads and two output leads (plug wires).

I measured the two input leads. and got 2.5 ohms of resistance.

Thank you! My coils haven't come yet, and I wasn't sure which leads to check. I believe in the other thread on CB900 coils on a 550, the poster mentioned that he had two live leads left over...I just wondered if it made a difference which live lead you left unused...

I'll go post my question to that thread too...   ;D
...stock 1972 CB500 '500 Four' undergoing re-assembly...
...Stock 1972 CL450 'Scrambler' also being re-assembled...

amattel

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well, there are two black and white leads which actually are both spliced from a single black and white lead.

there is also one yellow lead and one blue lead.

On my 750k2 - the yellw lead and the blue lead connect right to yellow and blue on the harness. though, like he said in the post, you have to cut off the multi-wire connector on the cb900 coils and install female bullets ont he red and the blue wire.  I put a male bullet on the black and white wire and plugged it in where the old coils black and white wire plugged in.

Thats what I did for the 750... don't know if your is different.

amattel

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I have a new issue now.  Since I installed the cb900 coils and gerex cdi my kill switch doesn't do anything.  The engine just keeps on running no matter where the switch is.

I don't remember by passing anything so I am a little confused as to how this happened.

Is the kill switch on the negative or positive side of the circuit from the coils and ignition switch?

When I look at my wiring diagrams I can't even find the kill swicth.

Has anyone here had any experience with this?

thanks,

Adam

Offline cben750f0

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looking at the wireing diagram, the kill is on the black/white wire......if the switch was working it should cut [ower to the coils.... you haven't cooked your kill switch some how?.... i would think it had more to do with the kill switch rather than the coils.... check the sitch..... peace
you are never to old, to act like a kid... be safe
funny thing,chasing someone down hill on a bike 30 years older than theirs..
he said \\\\\\\'it was like watching a 250kg unguided weapon getting stuck up you bum\\\\\\\ http://www.bikepics.com/members/trixtrem/

Offline Pinhead

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Would these coils also work on CB650's? Specifically the '79 model.
Doug

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GM HEI Ignition Conversion

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Offline cben750f0

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mate i dont see why not, im using VF1000 coils.... though if you are runnin points the lower ohms rating might cook them.... but i wouldnt know... all you can do is try.. let us know.... peace
you are never to old, to act like a kid... be safe
funny thing,chasing someone down hill on a bike 30 years older than theirs..
he said \\\\\\\'it was like watching a 250kg unguided weapon getting stuck up you bum\\\\\\\ http://www.bikepics.com/members/trixtrem/

Offline Pinhead

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Are they any stronger? My coils seem to be working fine, but if I can get a hotter spark than it could be worth it. The CB650's have electronic ignition from the factory.
Doug

Click --> Cheap Regulator/Rectifier for any of Honda's 3-phase charging systems (all SOHC4's).

GM HEI Ignition Conversion

Quote from: TwoTired
By the way, I'm going for the tinfoil pants...so they can't read my private thoughts.
:D

Offline Bodi

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Have a look at the Gerex wiring to the coils, this is a multifire CDI ignition I think and probably has its own wires to both sides of the coil. Since the kill switch shuts off the original (black) power wire to the coils, if you aren't using that wire then there's naturally no killing. You could wire the Gerex DC power feed from the black power wire for the coils. That would preserve the killswitch. Where did you pick up power for the ignition, the brake light switch (pretty common spot)?

amattel

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Have a look at the Gerex wiring to the coils, this is a multifire CDI ignition I think and probably has its own wires to both sides of the coil. Since the kill switch shuts off the original (black) power wire to the coils, if you aren't using that wire then there's naturally no killing. You could wire the Gerex DC power feed from the black power wire for the coils. That would preserve the killswitch. Where did you pick up power for the ignition, the brake light switch (pretty common spot)?

Thank you for that thought, Bodi.  I originally grabbed power from  under the left sidecover and disocvered via a dead battery 3 days later that I had bypassed ignition switch  ;D so I used the suggestion of the dyna III installation instructions and spliced it into the power wire going into the coils.  There is a black&white wire going into each coil .  There is also a green and a purple wire coming from the gerex one of which goes to each coil as well.

I am a little confused by this black power wire thing... isn't black supposed to be ground/negative?

so are the green and purple wires power and the black ground?..

so here's a description of all the wires going into/out of the gerex and magnetic timing piece .

Gerex...four wires coming from magnetic timing sensor (Yellow, Orange, Brown, Green)
           Black wire to Grounding bolt on engine case.
           Purple wire to a coil
           Green to other coil
           Red spliced to black/white ahead of coils

The gerex's power wire (red) is tied to coil power.. which ought to be that controled by the kill switch...  Would the Gerex cause higher voltage to be running through the kill switch and could that have fused a perhaps already borderline switch?

thank you,

Adam


           

amattel

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Are they any stronger? My coils seem to be working fine, but if I can get a hotter spark than it could be worth it. The CB650's have electronic ignition from the factory.

they are supposed to be stronger.  this is a common upgrade ffrom what I understand.

Offline Terry in Australia

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I don't think the CB900 coils are any better than those on the CB650, as they're pretty much the same generation of technology, and both ran OEM EI's. Cheers, Terry. ;D
I was feeling sorry for myself because I couldn't afford new bike boots, until I met a man with no legs.

So I said, "Hey mate, you haven't got any bike boots you don't need, do you?"

"Crazy is a very misunderstood term, it's a fine line that some of us can lean over and still keep our balance" (thanks RB550Four)