1972 CB125 Project

[loser69]

Just bought this for nearly nothing. Don't know much about them at all but always wanted a single cylinder honda cafe. Going for a minimal chop, minimal investment cafe thumper I can drive to work. It sat outside for a long time but seems like with a little cleaning it will fire up. Anyone have a link to 12v conversion and is a battery eliminator possible with these little guys? I've searched around a little and can't seem to find much.

Here's how it sits now right after I got it.

[Guest]

Conversion is easy peasy, I convert all my 6v bikes to 12v when I get them. On old 6v systems the battery acted as a regulator as in excess was sent back into it, well the idea didn't really work so well because anytime you were under maybe 4 to 5k rpm all lights were being powered just off of the battery storage, when the bike got at that RPM 5k ish it typically generated around 10k volts to quickly charge the battery back up...

The bad news is if you stick with 6v you'll always have a weak shitty electrical system. The good news is, since the stator output so much voltage it'll maintain a 12v great, of course the old rectifier has to go, a radio shack dual bridge rectifier is cheap and does the job great even has a hole in the center to use for mounting and costs under 5 bones. Don't need a regulator since the excess voltage is used to charge the system.

Hooking the new RS rectifier up: The bent post is the positive diagonally across from it is ground/negative. You'll have 4 wires off the old rectifier look at a diagram to find the positive rectifier wire hook it up, either jump a wire to ground or hook to negative from diagram if one is present diagonally across to the other post, the other two wires do not matter which post as both are AC outs.

Here's a picture to aid what I'm talking about:


Next, change all of your bulbs out to 12v, and use smallest drawing headlight bulb you can find no more than 35W is best, and if you can hook LED's to the other lights the brighter the head beam will be, less chances of dimming or flicker at idle and low speed due to no charging taking place... from low rpm, the secondary stator winding does the charging, the primary winding keeps it running.

If you're using blinkers you need a 12v flasher, and you need to bump the main fuse up to a 15A with the conversion.

Power source: You can use a battery or a large capacitor make sure the capacitor you use is unidirectional meaning the voltage only exits out of one post not both.

And well that's all there is to it.

Benefits: Faster starts, charging RPM drops to about 2K range instead of the 5k range, horn much louder, and your not gonna play nanny to a battery, and you can hook in a 12v accessory cigarette plug if you want to.

Some see this as a negative: Starter spins faster if you have one. I don't see it as a negative, faster spinning flywheel equals faster start equals less wear in the long run or at least balances it out instead of dragging it with 6v.

My two current bikes with the conversion:

My 150cc CA95 can sit over 8 months and still be holding 12v or better... too bad gas can't do the same. My CM185 is converted to 12v and has dimming issues, because I'm still running the stock 6v rectifier on it, it's getting chopped soon so I haven't bothered changing that part out yet, but works well enough as it is for now(battery hasn't ever died).

Quick part list:
RS Dual bridge rectifier
12v bulbs
15A fuse
12v battery or capactior
12v flasher if running blinkers

If you have any further questions about it, or need electrical help when hooking it all up feel free to ask.

[loser69]

Conversion is easy peasy, I convert all my 6v bikes to 12v when I get them. On old 6v systems the battery acted as a regulator as in excess was sent back into it, well the idea didn't really work so well because anytime you were under maybe 4 to 5k rpm all lights were being powered just off of the battery storage, when the bike got at that RPM 5k ish it typically generated around 10k volts to quickly charge the battery back up...

The bad news is if you stick with 6v you'll always have a weak shitty electrical system. The good news is, since the stator output so much voltage it'll maintain a 12v great, of course the old rectifier has to go, a radio shack dual bridge rectifier is cheap and does the job great even has a hole in the center to use for mounting and costs under 5 bones. Don't need a regulator since the excess voltage is used to charge the system.

Hooking the new RS rectifier up: The bent post is the positive diagonally across from it is ground/negative. You'll have 4 wires off the old rectifier look at a diagram to find the positive rectifier wire hook it up, either jump a wire to ground or hook to negative from diagram if one is present diagonally across to the other post, the other two wires do not matter which post as both are AC outs.

Here's a picture to aid what I'm talking about:


Next, change all of your bulbs out to 12v, and use smallest drawing headlight bulb you can find no more than 35W is best, and if you can hook LED's to the other lights the brighter the head beam will be, less chances of dimming or flicker at idle and low speed due to no charging taking place... from low rpm, the secondary stator winding does the charging, the primary winding keeps it running.

If you're using blinkers you need a 12v flasher, and you need to bump the main fuse up to a 15A with the conversion.

Power source: You can use a battery or a large capacitor make sure the capacitor you use is unidirectional meaning the voltage only exits out of one post not both.

And well that's all there is to it.

Benefits: Faster starts, charging RPM drops to about 2K range instead of the 5k range, horn much louder, and your not gonna play nanny to a battery, and you can hook in a 12v accessory cigarette plug if you want to.

Some see this as a negative: Starter spins faster if you have one. I don't see it as a negative, faster spinning flywheel equals faster start equals less wear in the long run or at least balances it out instead of dragging it with 6v.

My two current bikes with the conversion:

My 150cc CA95 can sit over 8 months and still be holding 12v or better... too bad gas can't do the same. My CM185 is converted to 12v and has dimming issues, because I'm still running the stock 6v rectifier on it, it's getting chopped soon so I haven't bothered changing that part out yet, but works well enough as it is for now(battery hasn't ever died).

Quick part list:
RS Dual bridge rectifier
12v bulbs
15A fuse
12v battery or capactior
12v flasher if running blinkers

If you have any further questions about it, or need electrical help when hooking it all up feel free to ask.

This is exactly what I was looking for and very descriptive! Thanks dude, can't wait to try this out with a cap. Probably only going to have a headlight and break lamp, Indiana law doesn't require turn signals. What about the coil, mine says 6v right on it?

[Guest]

Coil will be fine, make sure it's wired all right to be safe and certain, typically coils are rated for up to 20-24v spikes, and can run much higher than rated, the ohms is the most important number on a coil. Where it's a point system never leave the key in the "on" position for any reason other than running it for any amount of time over 20 seconds max, unless you wanna start burning the coil up, this is also why you wanna make sure the wiring is right or the same thing can happen. The key should break the power circuit to the coil if it doesn't... bye bye coil, it can also possibly start a fire if not discovered in time.

[loser69]

Started the CB100E motor tear down in my hillbilly basement shop (I'm poor!). Looks like it's in real great shape for having sat outside for several years. It had low miles on it but appears like it was rebuilt before it sat. The cam was hard to get out, had to use channel locks to twist it around the valve's pressure to slide out the head's cutouts. Found a decent manual for it here and printed it off at work. Thinking about boring it out. Found some information on using CB750 sleeve/piston and CB125 crank. Anyone done this?





Planning on polishing all the aluminum cases/covers by hand, we'll see how that goes. Started with too coarse grit (been a while since I've done this).



Frame/swing arm are out for sand blasting. When they're back going to start chopping away.

[HulkJoegan]

Keep updates coming, love seeing these small bikes. I'm working on a 73 cb125 myself

[CXDanimal]

Hi Jetblack
this is a great post thanks!
is this the rectifier you were talking about? http://www.radioshack.com/nte-nte530...-high&start=38

I take it the v and a important to get right?
I have also switched over to a lithium battery ...any idea of the ideal size?

Thanks again

[CXDanimal]

Conversion is easy peasy, I convert all my 6v bikes to 12v when I get them. On old 6v systems the battery acted as a regulator as in excess was sent back into it, well the idea didn't really work so well because anytime you were under maybe 4 to 5k rpm all lights were being powered just off of the battery storage, when the bike got at that RPM 5k ish it typically generated around 10k volts to quickly charge the battery back up...

The bad news is if you stick with 6v you'll always have a weak shitty electrical system. The good news is, since the stator output so much voltage it'll maintain a 12v great, of course the old rectifier has to go, a radio shack dual bridge rectifier is cheap and does the job great even has a hole in the center to use for mounting and costs under 5 bones. Don't need a regulator since the excess voltage is used to charge the system.

Hooking the new RS rectifier up: The bent post is the positive diagonally across from it is ground/negative. You'll have 4 wires off the old rectifier look at a diagram to find the positive rectifier wire hook it up, either jump a wire to ground or hook to negative from diagram if one is present diagonally across to the other post, the other two wires do not matter which post as both are AC outs.

Here's a picture to aid what I'm talking about:


Next, change all of your bulbs out to 12v, and use smallest drawing headlight bulb you can find no more than 35W is best, and if you can hook LED's to the other lights the brighter the head beam will be, less chances of dimming or flicker at idle and low speed due to no charging taking place... from low rpm, the secondary stator winding does the charging, the primary winding keeps it running.

If you're using blinkers you need a 12v flasher, and you need to bump the main fuse up to a 15A with the conversion.

Power source: You can use a battery or a large capacitor make sure the capacitor you use is unidirectional meaning the voltage only exits out of one post not both.

And well that's all there is to it.

Benefits: Faster starts, charging RPM drops to about 2K range instead of the 5k range, horn much louder, and your not gonna play nanny to a battery, and you can hook in a 12v accessory cigarette plug if you want to.

Some see this as a negative: Starter spins faster if you have one. I don't see it as a negative, faster spinning flywheel equals faster start equals less wear in the long run or at least balances it out instead of dragging it with 6v.

My two current bikes with the conversion:

My 150cc CA95 can sit over 8 months and still be holding 12v or better... too bad gas can't do the same. My CM185 is converted to 12v and has dimming issues, because I'm still running the stock 6v rectifier on it, it's getting chopped soon so I haven't bothered changing that part out yet, but works well enough as it is for now(battery hasn't ever died).

Quick part list:
RS Dual bridge rectifier
12v bulbs
15A fuse
12v battery or capactior
12v flasher if running blinkers

If you have any further questions about it, or need electrical help when hooking it all up feel free to ask.

Hi there, thanks for the awesome post. i am doing a 12v conversion on my cb125. would it be a good idea to change the coil over to a 12v while i'm at it? any thoughts on what might be a suitable one to use?

cheers Danny

[dereck]

wow, I am new here and I can't believe I found a link that exactly address my concerns. Thanks guys.. I have all the issues associated with a 6 V system.... And I want to upgrade to 12V. Thanks Jetblack for your detailed instructions. I can not believe it is this easy and I have been a slave to my 6V batt for for 3 years since I rebuilt my bike. Should I get a new harness to go with the upgrade? Or will the old harness work? and is it as simple as changing the rectifier? Please state the obvious for newbees like me. Any way to test to make sure the output from the stator is sufficient? thanks again...

[dereck]

ok now what?


I have the old rectifier off. how do I add the new one? I have all the parts recommended above.. Battery and all!! Please help!!!

Am I missing something?

[jethro57]

wow, I am new here and I can't believe I found a link that exactly address my concerns. Thanks guys.. I have all the issues associated with a 6 V system.... And I want to upgrade to 12V. Thanks Jetblack for your detailed instructions. I can not believe it is this easy and I have been a slave to my 6V batt for for 3 years since I rebuilt my bike. Should I get a new harness to go with the upgrade? Or will the old harness work? and is it as simple as changing the rectifier? Please state the obvious for newbees like me. Any way to test to make sure the output from the stator is sufficient? thanks again...

if the old harness is intact (not altered by the PO) then keep it, if its been messed with get another one, should nt be to expensive
excellent post there Jet, BUT
turn signals on a cafe ?

[dereck]

if the old harness is intact (not altered by the PO) then keep it, if its been messed with get another one, should nt be to expensive
excellent post there Jet, BUT
turn signals on a cafe ?

Yes turn signals need to be street legal in Florida. My harness is good. I am just trying how to hook up the rectifier. looking at the phots above.. Any suggestions?

[CraiGORE]

1 wire to battery positive. It's marked "+" on that exact rectifier. 1 wire to ground. It's marked "-"Original rectifier was grounded to frame so you won't find one on the original harness. So literally just ground that post with a wire going to the frame. Two wires from original rectifier go to stator. Hook those 2 wires to the new rectifier it doesn't matter their orientation they take AC and convert to DC. Just make sure ground and positive are correct.

It's an easy replacement you just need some blade connectors, maybe solder and shrink wrap. And a wire for ground

[dereck]

1 wire to battery positive. It's marked "+" on that exact rectifier. 1 wire to ground. It's marked "-"Original rectifier was grounded to frame so you won't find one on the original harness. So literally just ground that post with a wire going to the frame. Two wires from original rectifier go to stator. Hook those 2 wires to the new rectifier it doesn't matter their orientation they take AC and convert to DC. Just make sure ground and positive are correct.

It's an easy replacement you just need some blade connectors, maybe solder and shrink wrap. And a wire for ground

Thanks for that!! Appreciate it.. Excuse my ignorance... I have a red, yellow, Pink and green going into the Rectifier.. Green ground? Red live? And the other two are interchangeable? So once I do this and hook up the 12v batt. (and bulb) I should be good? Am I missing anything else? Is there any test I should do before I power so I don't blow the coil or something?

[CraiGORE]

red goes from the new rectifier to your battery or it will go to a fuse holder. I am looking at a cb125 diagram right now green is ground; if you were to trace that wire through the harness it attaches somewhere to the frame.
Just make sure red goes to + and green goes to - on your RS rectifier

yellow and pink come from the stator. yes they are interchangeable.

you will not blow out a coil just make sure that your fuse is good. it probably takes a round glass type and sometimes you cannot see if they're blown...annoying tracing wiring gremlins when the problem was a blown fuse.. ask me how I know haha

im working on a cb160 at the moment, I love geeky small displacement hondas