How to run a CB77 without a battery?

1204_cb77 · Post by **1204_cb77** » Sat Apr 27, 2019 10:11 pm

revlover wrote:A word about your ignition coils.... The coils in your pictures are automotive type coils. As the printing on the side indicates, an external ballast resistor is required for each of the coils. Because of their very low primary resistance, a resistor or resistive wire is used to prevent excess current flow through the coil. If you operate these coils at 12 volts or higher, excessive current flow will result and your points will likely be damaged. In addition, the combined current consumption of the two coils may be beyond the output capability of the stator. A better choice might be some universal coil designed for motorcycles. EMGO makes universal cylindrical coils which have a more suitable primary resistance and will fit nicely in the tight space under the tank. If however you insist on using the auto coils, a suitable resistor must be sourced for each coil. The resistors should be wired inline with the positive wire and be mounted somewhere with adequate air flow because of heat. Probably not the best idea if you want the wiring to remain simple though. Hope this helps.

Here is a link for the coils.
https://www.amazon.com/EMGO-Ignition-Co ... 1MNKKZ829N

Thanks for the word on this..I have some MSD Ignition coil wiring I plan on using...I can post up a pic of it for reference. But I don't think it is resistance wire...I do recall seeing a white plastic thing in the box that had two terminal posts on it. Pretty sure those were the old resistors. If so, i'll pick up some new fresh ones. Thanks again for the heads up! I also found this very simplified diagram online that appears to be pretty close to how I will wire up my system. I will just split the end that goes from the ballast resistor into a dual lead to both (+) on the coils.

I did find this though on another site that states if the coil does say 12v on them and will be on a twin cylinder resistors are not needed...

upload pic

Cheers,
Max

revlover · Post by **revlover** » Sun Apr 28, 2019 10:37 am

Well looks like we're getting closer. I don't know what logic is behind the no resistor needed for twin cylinders notion. Since both coils will be energized at the same time, albeit momentarily, separate resistors should be utilized. You will need an ohm meter to make the final decision on a resistor. The stock honda coils had a primary resistance of about 4.0-4.5 ohms and no extra resistance was required. If your new coils have a much lower measurement, then you will need a resistor that will make the total resistance of one coil + ballast resistor closer to 4 ohms. It's okay to be a little off from that number, but the lower overall resistance will mean higher current. It is very important to note that these bikes had no voltage regulator and thus the stator output was designed to closely match the theoretical load of the electrical devices with just a tiny bit extra to charge the battery. A modern rectifier/regulator combo will eliminate the risk of overcharging the battery, but it won't make the charging system any stronger. Therefore, it is still somewhat important to stay close to original specs when choosing electrical components. I hope this is helpful to you instead of more confusing. Please keep us posted on your progress.

1204_cb77 · Post by **1204_cb77** » Sun Apr 28, 2019 12:44 pm

revlover wrote:Well looks like we're getting closer. I don't know what logic is behind the no resistor needed for twin cylinders notion. Since both coils will be energized at the same time, albeit momentarily, separate resistors should be utilized. You will need an ohm meter to make the final decision on a resistor. The stock honda coils had a primary resistance of about 4.0-4.5 ohms and no extra resistance was required. If your new coils have a much lower measurement, then you will need a resistor that will make the total resistance of one coil + ballast resistor closer to 4 ohms. It's okay to be a little off from that number, but the lower overall resistance will mean higher current. It is very important to note that these bikes had no voltage regulator and thus the stator output was designed to closely match the theoretical load of the electrical devices with just a tiny bit extra to charge the battery. A modern rectifier/regulator combo will eliminate the risk of overcharging the battery, but it won't make the charging system any stronger. Therefore, it is still somewhat important to stay close to original specs when choosing electrical components. I hope this is helpful to you instead of more confusing. Please keep us posted on your progress.

Makes sense, I will pick up two new ones for each cylinder. I am replacing everthing with new. New coils, new condensers and new resistors. I'll keep you posted. Thanks again!

1204_cb77 · Post by **1204_cb77** » Sun Apr 28, 2019 9:25 pm

I am wanting to confirm stator to the new Kohler rect/reg. wiring.

There are 3 terminals on the unit.

Yellow & pink I will tie together to one terminal
Brown wire will go to a terminal
Last terminal will go to battery (+)

I am leaving the light green / red wire alone as it is the neutral wire.

Lastly, the unit itself will ground through the mounting posts.

I picked up my new ignition ballasts today along with another new coil and two new condensers. Getting this beast wired up tomorrow!

Cheers!
Max

1204_cb77 · Post by **1204_cb77** » Mon Apr 29, 2019 10:34 am

Also wanted to confirm. I am using a on/off toggle switch.

From the diagram I see the Ignition ground running to the coils and the red wire fused coming off the battery (+).

Or, with my switch as there are only two leads. One wire from battery (+) and the other lead will be grounded?

I figured I'd wire it up like the schematic as the power will then run through the switch in the (ON) position and kill 12v power once toggled to the (OFF).

Sorry, more or less thinking out loud on here. Typing helps me think it through haha :)

Here is a similar switch to what I am using: https://www.amazon.com/gp/product/B01EL ... QJ81HW2X75

revlover · Post by **revlover** » Mon Apr 29, 2019 1:29 pm

Sounds good. An inline fuse might be a good idea too. 10 amp - 15 amp should do nicely.

mike in idaho · Post by **mike in idaho** » Mon Apr 29, 2019 6:37 pm

The main reason for using 4 ohm + impedance coils in this application is to keep the current load down for the points. Super low impedance coils mean burnt points. Amps times volts equals watts, the total watts needed to fire the spark plugs remains the same, use whatever coils are compatible with the points system and you can't go wrong.