Topic: Connecting 79 coils to a K5

[Kinch]

First off please excuse my ignorance.

I picked up a pair of coils off of a 1979 CB750 to replace the bad ones on my K5 and have just replaced the spark-plug wires with new ones.

A couple dumb questions: Would just a standard 14 gauge copper wire from Auto zone work to replace the wires that go into the starter and wiring harness (the ones that are built in on the K5 coils)? Also, as the coils are shaped differently and do not fit the mounting bars from the K5 coils is there a good way to attach them to the bike?

Any info greatly appreciated.

Thanks

[Triffecpa]

yes, standard Autozone copper core wire will work fine. 

I can't remember how the stock coil set up is mounted, but basically any mounts that secure them solidly to the frame will work.  Nothing magic about the stock ones.  You will want to make sure that the coils don't hit the underside of the tank though as the newer ones are slightly wider at the end where the spark plug wires attach.

TR

[Soos]

That will be a change in ohms of your coils wown't it?
Is there anything needed to accommodate for this?


'79DOHC cb750 coils are 2.5'ish ohm coils, aren't the K5's coils 5.0 ohm?




mabey hondaman could steer you in the direction of what you want to know.



l8r

[eldar]

Well coils such as this are a common upgrade. Points will tend to wear out sooner, same with condensers. There will be more current draw so be sure your charge system is working good. I might even suggest going to an electronic regulator as they are usually more efficient and allow better charging at lower rpm.

[Kinch]

Thanks all, forgot to mention that the stock ignition has been replaced with a Dyna S, someone on a previous post stated the 79 coils and Dyna S should work fine together. I'll have to check out the regulator to see if it's stock or not.

[eldar]

The dyna will be fine with the lower ohm coils. It is the rest of the system you need to make sure is in top shape.

[Kinch]

Noted, thanks again.

[Kinch]

Ok, so I've gone through and cleaned or replaced any iffy connections throughout the bike. I attached new copper wire with coated female blade connectors to the back of the coils. The connections on the back of the coils are marked positive and negative, do the positive wires connect into the black&white power wire and the negative wires connect to the blue and yellow wires or vice-versa?

Regulator is stock, I'll look into an electronic one.
Edit: is this what you're referring to?
http://www.z1enterprises.com/detail.aspx?ID=3267

[Patrick]

If those are 2.5 or 3-ohm coils you may want to consider adding a couple of resistors in line with the power connections. Hondaman sells them. I am using the coils from an early 80s VT750 on my K0. They are 3-ohm. I use Hondaman resistors along with a Hondaman igntion, which you do not need. I am not altogether certain your electrical system will handle 2.5 ohm coils without them. A 750 can do 3-ohm coils, but resistors will help reduce draw on the system.

[Kinch]

Yeah, I was looking at the manual for my DYNA and it listed 3 ohm as the lowest recommended resistance so I'll probably do that, thanks.

[Kinch]

Ordered some 1 ohm resistors (thanks Hondaman), the coils are 2.7 ohms.

I know it's a dumb question but how do the wires coming off of the coils that are listed + and - correspond to the black&white striped and blue and yellow wires? Does + = black and white and - = Yellow and Blue or is it the other way around?

[Patrick]

Black and white is power to the coils. Blue and yellow is negative to the points (Dyna).

[Kinch]

Thanks 

[Kinch]

Meh. From how I understand it, the black and white wire coming out of the wiring harness should attach with a push-down clip to the red wire from the DYNA and the + connections from the coils but when I check the power on that B&W wire directly where it comes out of the wiring harness with a circuit tester it doesn't have power going through it. There is, however, a solid black wire out of the harness that does have power going through it and is not attached to anything  .

As usual when it comes to anything electrical, I'm confused.

[Duke McDukiedook]

Don't worry about that black wire. clip in the red to the B+W wire and see if it works.

[Kinch]

I did and no spark. - connectors from the coils going to the Blue and Yellow and both + wires coming from the coils clipped with the red from the DYNA to the Black and White coming from the harness but still nothing. Shouldn't the B&W wire out of the harness light up the circuit tester though?

Never mind, something else is going on with it. Need to trace a couple other things before I proceed...