Topic: Resurrecting 1973 CB125

[Wind-Rider]

Hi All,

I'm new to the site and hope there are CB125 enthusiasts out there who might be able to assist.
I've been reading posts on this site for a bit now, and have noticed unlike a number of other forums, that there is always good response from those affiliated with SOHC/4.  Kuddos

Last time I  fired her up was in  about 1992, so she's has just been sitting in storage for quite some time, waiting for mama to decide she wanted to ride next to me instead of behind me.  I'm pretty close to completing renovations.  Here is what was changed.

New rectifier to replace the old selenium rectifier
New points
New Air Filter
Rebuilt Carb
New fork seals and guides
Cleaned out oil filter screen (pretty clean anyhow), and changed oil
New speedo indicator bulbs
New cables (all)
De-rustified gas tank. 
New paint on tank can wait.

She really needed more cleaning than anything.

Anyhow, I bench tested the Stator, new rectifier (old selenium didn't test correctly on all wires), coil (primary & secondary side), ignition switch.  all had good continuity.  The primary tested at 2.3 Ohms, and the secondary tested at 14.9 ohms (with the plug cap on).  Not sure if those are good readings or not, as I never had an owners manual - just a Clymers manual.  I did not do anything to the top end as compression tested at 110 psi.  a little lower than I would have liked to see it, but passing.

I adjusted the cam chain, set the inlet and exhaust valves at .002" and initial point gap at .014".
My problem arose when I'm setting the points with a test light (made from an extra 6v indicator light).  When hooking the (+) test lead of the test light (which I soldered to the (+) part of the bulb) up to the points nut, and the (-) lead (which I soldered to the (-) side of the bulb) grounded to engine , and then turning the ignition on, I expected to see the bulb light up when the points are open, and for the light to go out when the points are closed (no gap).  My test light stays on no matter whether the point are opened or closed.  Kind of wondered why I couldn't get spark at the plug.

Now, I did have spark at the points when I inadvertently had the ignition on, and I check the point gap with a feeler gauge.  when the gauge touched both sides of the open points, I got a surprise, as I thought the ignition switch was off.  I don't believe the issue is the way the wires are hooked up, as I'm using the same wiring harness since I had good continuity in all wires.  I did replace a few of the bullet ends though by soldering on new ones.

I'm just kind of at a loss on what to check next. I'm wanting to think electrical, but not sure. I am a so, so, wrench however electrical is not my strong point.

any help would be appreciated.  I go to retrieve my other bike from winter storage next week, and would like to be able to start mama out on the finer points of a motorcycle clutch on the 125.

Even though I don't think the issue is in the way it is wired, I've attached a photo of how the wires to the points, condenser, coil and ignition are connected.

[b52bombardier1]

I'd recheck your points gap. I think you will also eventually need to replace your points condenser if you see extensive arcing and sparking at the points with the bike running and the points cover removed in a dark garage.

Do you have spark at the plug? Have you checked the spark advancer for full movement of the counterweight arms?

You don't mention it but you need a healthy battery on this bike for good spark ignition.  The battery is also the voltage regulator. Without a healthy battery that can accept recharge current,  you will blow every lamp on the bike.

Rick

Sent from my SAMSUNG-SM-N900A using Tapatalk

[grcamna2]

+1 on checking the condenser. I would also make sure the points lead wire isn't gounding-out inside the points plate,etc.

[becken]

Make sure the contact surfaces of the points are clean and not burned. Dress them with a points file or fine sandpaper and then clean them with alcohol.

[Wind-Rider]

Hey Rick,

Thanks for the reply.

I did install a new set of points, plug, and do have a new battery.  I keep the battery on a trickle charger, so its always been testing at 6.4v when I take it off to try and check electrical work.  I haven't removed the spark advance, but will do that to check the counterweight arms for movement.  I just retested the condenser for continuity, and with one of my testers it toned, and with the other one, the display went from 1 to 0.

If you think of anything else. Do not hesitate to shoot me a line.

[Wind-Rider]

grcamna2 and  becken,

Thanks for your suggestions.  Condenser seams to be a commonality, I will purchase a new one even though the current one tests out.  Tests can be wrong.  I did consider the points wire grounding out on the plate, so I adjusted it a bit, maybe I should adjust again just to make sure, or maybe install some electrical tape around the area that is really close to the side of the casing (there's just not a lot of room in there).

I doubt I'll  have the opportunity to get make these adjustments and cleaning for a couple of days. Not sure about filing on a new set of points, but if the arcing with the feeler gauge didn't hurt them, a fine points file shouldn't hurt them.

I just couldn't figure out why my test light would stay on all the time.  It's like I have an open circuit even when the points are closed, or a closed circuit when the points are open.  Did I mention electrical is not my strong point?

I'll let you all know after I've had the opportunity to get back to it.

Michael

[RAFster122s]

So, green on your bike is not Ground like on the SOHC/4s?
Black is normally switched power on the SOHC/4s. Red is battery power to the switch.

Blue will be going to the points won't it?  As it has to be connected to the coil to complete the path for charging and when the points open for it to fire the secondary side.

I am presuming your plug cap is removable. If so, unscrew it and cut the plug wire back about 1/4" or so. Before reattaching the cap you need to test it for ohms. If it is original it is likely to be 10k Ohm if like the SOHC/4 bikes. But more modern NGK caps are going to be 5Kohm caps. (or zero)  you need either resistor caps or resistor plugs, but not both.
Test your secondary without the plug cap attached.
Now, it would be helpful to see your wiring diagram.

It sounds as if you may have a grounding problem on your points wiring at the points plate from some of the description above.  You may wish to test for grounding of the terminals by a test lead on the wire and the other on the points plate. If you see zero ohms you are seeing a grounding problem.  Double check your mica insulators to be sure you have your connections right.  But, then again, you are seeing your points spark when they are opened...then you most likely do not have a problem.  I can't imagine you crossed the wires hooking it up but we all make mistakes.  Doesn't hurt to check your work to rule things out as an issue.
Would not hurt to replace the buggered up screw in the points plate.  If it stickys/siezes, then it is going to be a real pita to remove later.  Do you have JIS screwdrivers?  Really worth the investment. Vessel are very very good quality, but the Hozan brand on Amazon are adequate JIS screwdrivers as well. Motion Pro now offers a T wrench with the P1, P2, and P3 bits.  You can buy a two pack of the 1/4" hex JIS bits in two packs for each size as a replacement. (saving you from buying the T wrench). The are less than $3 for a pair and Dennis Kirk carries them as probably do other bike suppliers.  A local Honda dealer or bike shop could order them in for you with one of their other orders, or by themselves. Just ask them the price first. Hate to be charged double or foot the bill from them for the shipping when you could order a few things yourself and have it direct.
Then you put your bits in a hex driver or hex driver extension and you have some JIS screwdrivers, capable of others you might need (hex key bits if you replace JIS case screws or carb bowl screws, etc. with socket headed hex screws.)
David

[b52bombardier1]

Excellent advice on the JIS screwdrivers.  I can't live without them on these bikes. "Vessel" made my set of three and McMaster Carr carries the set.

Rick

Sent from my SAMSUNG-SM-N900A using Tapatalk

[grcamna2]

grcamna2 and  becken,

Thanks for your suggestions.  Condenser seams to be a commonality, I will purchase a new one even though the current one tests out.  Tests can be wrong.  I did consider the points wire grounding out on the plate, so I adjusted it a bit, maybe I should adjust again just to make sure, or maybe install some electrical tape around the area that is really close to the side of the casing (there's just not a lot of room in there).

I doubt I'll  have the opportunity to get make these adjustments and cleaning for a couple of days. Not sure about filing on a new set of points, but if the arcing with the feeler gauge didn't hurt them, a fine points file shouldn't hurt them.

I just couldn't figure out why my test light would stay on all the time.  It's like I have an open circuit even when the points are closed, or a closed circuit when the points are open.  Did I mention electrical is not my strong point?

I'll let you all know after I've had the opportunity to get back to it.

Michael

'Wind-Rider',
The other thing that can be a problem is where the points wire attaches to the points,where the points spring mounts there.. it has 2) little fiber washer/insulators and one small one that fits inside between there around the screw so the inside threads of the screw doesn't ground-out on the points plate;if that tiny little insulator that protects the threads of the screw inside is missing,the screw will ground-out on the points plate.

[tbpmusic]

  My test light stays on no matter whether the point are opened or closed.  Kind of wondered why I couldn't get spark at the plug.

That means the light bulb is your only path to ground.
What was said about wire colors is correct for all these old Hondas - green is ground, black is hot after the ignition switch.
Here's your wiring diagram - it says CB100, but it's the same for the CB125 (single, not the sloper twin).

[Wind-Rider]

Hi All,

I returned home a little earlier tonight so I though I would delve into some of the suggestions I have received. 

This is all going to read as pretty confusing, as I have so many thought going around in my head about this right now, I'm not sure I'm going to elaborate clearly, without repeating some ideas just in a different way.  If so, my advanced apologies.
 
First I took the points plate off tonight to look at the advance counter weights as Rick suggested.  Not sure that did me any good as I'm not sure what the advance was suppose to be doing.  I did notice that when I grabbed the advance b/w my thumb and forefinger, I could rotate it just a bit in one direction (maybe 5 or 10 degrees) until the weights would hit on the side of the advance unit (counter weights all the way out), and then I could return it to the starting point (counter weights in).  However when I put a wrench on the hex nut holding the advance unit in, and then turned the motor over with that nut, the weights didn't move at all.  As mentioned though since I'm not exactly sure what was supposed to happen, it could be working correctly?

While putting back together, I took the points apart to check on the fiber washer and make sure one of them went all the way through the opening to confirm the screw wasn't grounding out.  unlike my old set of points which had one of the washer going all the way through the points opening, the new set had both washer each going half way through the screw opening.  I considered replacing with the old one, but I didn't.  This might be a point of contention in the future.

Once I put everything back together, I took an Ohm reading as suggested.  Wouldn't have know to do that without the recommendation.  I took it 1st with the ignition switch off, and next with the ignition switch on.  I expected two different reading, however I read 1.5 Ohms in each test.  So even though I'm not sure what kind of reading I should be seeing, that was at least encouraging.

When I originally rewired (which wasn't really a rewiring as much as a reconnecting of all the wires , I used the CB100 wiring diagram.  As tpbmusic mentioned it is almost the exact same as the CB125 single, however since I only had the speedo and no tac, I used the CB100 diagram. Additionally, my front turn signals are grounded to the head light bucket as the CB100 diagram shows, instead of via a separate green wire as the CB125 wiring diagram shows.

I read somewhere that the green is normally the pathway to ground, however since it is a points based ignition, and the normal green ground wire connects to the points from the condenser, that the point plate then acts as the ground. I don't know it that's true or not, but it sounds plausible.

Also, just about everything I have read say a positive needs to go to the coil from the ignition (this would be the black wire as I only have the 2 wires coming from the ignition), and Red goes to the battery. Right now I have the black from the ignition going to the black from the coil. (not directly though, which I don't believe should matter, as all blacks are connected together at some point).  I guess I'm presuming the black from the coil is the hot wire for the coil, and the blue is the ground, which as it comes out of the coil goes into the condenser as blue, and out of the condenser to the points as green?  It all a little confusing to me.

The coil primary side only has the two wires coming from it.  Black which goes to ignition, and Blue which goes to the Blue wire from the condenser.  the only other wire is the green which comes from the condenser.  with only the green wire from the points left to connect, the green from the condenser must go to the points. That being said, the blue wire coming from the coil (Female connector) can connect to the points wire (Male connector) however this leaves only the green and blue from the condenser not connected to anything.  That would suggest they are to be connected together. This doesn't sound right though.

I originally had a ND X24ES-U plug, and a plug cap with a resistor in it.  I reinstalled a NGK DR8EA, and purchased an NGK plug cap without a resistor.  Prior to switching the resistor cap for a non resistor cap, I had good Ohm readings everywhere except when I placed the resistor cap on the plug wire - then nothing.  Now with the non resistor cap attached to the plug wire, I have a good Ohm reading.  If I remember that was around 15, which means 15K. With that knowledge it only tells me the old resistor cap was probably bad. Might tell someone that knows more about resistance, etc. something else.   I may have been able to install a new resistor cap and still come up with an Ohm reading, but is more than 15K needed?

I'm not exactly sure what a mica insulator is, unless it's the fiber washers on the points.  If it is, then the points spring, and the points wire connector are both on the outside, so isolated from the points. 

One last thing for now, then homework for a bit.  the arcing I had with the points open didn't occur on its own.  it only happened when I accidentally touched the feeler gauge to both sides of the points with the ignition off.  I don't know if that makes a difference or not, but thought I would clarify?

It sure is great brainstorming with everyone trying to help me get the 73' back up and running.

We'll get there.

Michael

[tbpmusic]

Your advancer would have nothing to do with whether or not you have spark, only when you have spark.......

[Wind-Rider]

Hey All,

I wound up buying a new condenser (didn't do this when I bought new points).  Installed the condenser, and double checked valve & points gaps, and the opening of the points in conjunction with the fire mark on the rotor, put gas in the carb., and it fired up on the 3rd kick.

Thanks to everyone who had an input in this.  now all I need to figure out is why my turn signals decided to go out.  They never did blink, but they at least used to always go on.  I'll get out the multi-meter this weekend and start testing for continuity in the wires.  my fear is it might be either the lighting wires from the stator, or from the rectifier.  And right after I bought a new relay to get them to blink - go figure.

Here's a photo of the bike.  Still have to attach the seat, but i want to be able to access the wires this weekend.  Will also need to try and find someone who can repaint the tank and side covers next winter.

Thanks Again,

Michael

[grcamna2]

That original paint is a bit faded but still very nice.  Glad to hear you have it running.