This cb125 is going to be the death of me

Ok I'll make this as short as I can, got a 1974 cb125 for free from my dads buddy. It was sitting for 30 years. The carb was disgusting and it had no spark and the tank was gross and rusty.

So I have done the following-
Clean the carb about 10 times, clean the tank and added fuel filter
Replaced coil, points and condenser and battery

Gapped the points, set the float height, set static timing and gone through with a multimeter to try to find and issue with wiring

Here is my issue. I charge the battery and start the bike and it runs great... for about 1 mile. Then sputters and dies. It feels like a fuel problem but when I take the carb off again its completely clean.

But then it seems like it's related to something electrical because when the lights are on it seems to bog worse.

I'm ready to light this bike on fire and forget about it. But on the other hand I REALLY want to ride it because for the 1 mile it works, it's fun as hell and I have the biggest dumb smile on my face. It's just aggravating the crap out of me because it's such a simple bike and I feel like the problem is going to be so ridiculous that I'll be ashamed

Literally any help at all would be greatly appreciated

How long does it have to sit before it fires up and goes again?

Whats the battery voltage shut down - key off - when it dies?

Whats the charging voltage at idle and 3krpm?

Gas cap vent clogged?

Vapor locked inline fuel filter?

Soon as it dies - quickly pull plug and see if it has spark.

Double check points gap.

Too tight and it will overheat coil.

Too wide and it won't have enough time to properly charge coil.

It will fire right up and idle right away but wont take any throttle. Battery voltage is 6.3v shut off but running it will get to 7.05v @ 4k rpm. Gas cap vent could be it but I cracked the gas cap a bit to take that out of the equation.

You migh have something with the fuel filter, I'm apprehensive to run no filter after all the crap I went through with the tank.

I will double check points gap. I did it yesterday and it was .013" at TDC

And ill have to make it die and pull the plug

I just went out after like 2 hrs of it running and the batt was at 4.2 v

swizbee42 said:

I just went out after like 2 hrs of it running and the batt was at 4.2 v

Click to expand...

Im sorry but just to be clear this is a 6 volt bike right. My 72 CL100 was 6v but I modded to 12 volt.

2 hours of riding it? various rpm?

4.2vdc seems weird as its charging w 7.05vdc. Possible Your battery may be bad even if it's newer.

Whats the voltage across battery terminals at idle?

Test the stator. Key off, unplug stator.

Set meter to ohms. Read between all three wires. 1 -2, 2-3, 1-3.

All 3 readings should be approx 1.0 ohms. If any is 0 = open. time for a new stator.

Or stator wires usually fail at bend. Through rubber grommet under cover. Or solder joints where the stranded wires are soldered to solid stator windings.

You can dig into find that. And make the repair.

trek97 said:

Im sorry but just to be clear this is a 6 volt bike right. My 72 CL100 was 6v but I modded to 12 volt.

2 hours of riding it? various rpm?

4.2vdc seems weird as its charging w 7.05vdc. Possible Your battery may be bad even if it's newer.

Whats the voltage across battery terminals at idle?

Test the stator. Key off, unplug stator.

Set meter to ohms. Read between all three wires. 1 -2, 2-3, 1-3.

All 3 readings should be approx 1.0 ohms. If any is 0 = open. time for a new stator.

Or stator wires usually fail at bend. Through rubber grommet under cover. Or solder joints where the stranded wires are soldered to solid stator windings.

You can dig into find that. And make the repair.

Click to expand...

yes it is a 6v bike, interestingly enough when i went back out the bike now gives me nothing when i turn the key on.....not even a directional light or anything, the horn will barley make any kind of noise. voltage across the terminals key off was 3.95v. so I definitly have a draw or short coming from somewhere I just dont understand. and in dont know if im smart enough to find it on my own

but i did test the stator wires (mine actually has 4 wires....) but i didnt get much of anything for a reading ( not sure if i did it right). so with that said and if i need a new stator and teh battery is questionable than i think now is probably as good a time as any to go to 12v right?

Yep, 12v sounds the way to go. I'll probably change mine over at some time. I think I have all the parts to do it.

Just need to get off my lazy butt and "git'er done".

I have a 72 CB100 and I just got it up and running. Just only been able to ride around the back yard.

Still need lights and I will try it on the street. Seems to bog a little in the yard, but not enough room to open it up.

You'll get her right, just stick with it.

Speaking of having a silly grin, I do to when I ride this little thing......fun as sh1t.

And on another note..........I feel the same way you do with my other bikes (CB750, and CB350F), ready to push them to the back yard and set fire to them.

For the life of me cannot get them to run worth a crap.

The 4th wire is the neutral switch. ;D

Just check between stator wires as above.

You need to find the problem at hand. Then consider the the 12v upgrade.

Does your bike still have the stock selenium rectifier ?

trek97 said:

Download and save the Official Honda shop manual from my drive.

https://drive.google.com/file/d/0B94qfPnRdKQadTg1dmk4eWJaaFU/view?usp=sharing

The 4th wire is the neutral switch. ;D

Just check between stator wires as above.

You need to find the problem at hand. Then consider the the 12v upgrade.

Does your bike still have the stock selenium rectifier ?

Click to expand...

Yes I believe the entire bike is original besides what I have replaced, so that would include the rectifier which I tested (again not sure if i did it right, used the diode function on the meter) but i got inconsistent numbers on it. 2 were relatively the same and one was way out in left field

WhyNot said:

Yep, 12v sounds the way to go. I'll probably change mine over at some time. I think I have all the parts to do it.

Just need to get off my lazy butt and "git'er done".

I have a 72 CB100 and I just got it up and running. Just only been able to ride around the back yard.

Still need lights and I will try it on the street. Seems to bog a little in the yard, but not enough room to open it up.

You'll get her right, just stick with it.

Speaking of having a silly grin, I do to when I ride this little thing......fun as sh1t.

Click to expand...

I want to get it done so bad, ironically I put it away about 4 years ago after doing all the same stuff with no results, I think that's why it's so frustrating.

What do you need for the 12v conversion, I've read like 5 different ways to do it

Ok I dont get it. Seems like everything checks out. I cleaned out the tank and carb again. Re gapped the points to .013" @ tdc. Replaced the fuel line and filter and rechecked the spark and float height as well. The stator and rectifier checked out per the service manual and I measured AC voltage out of the stator while running and I got like 50 AC volts @ 5k rpm I'm getting fuel and a big fat blue spark.....

The only 2 things are that I think the battery is suspect since it not brand spanking new or maybe I did the static timing wrong, but wouldn't that effect the entire rpm range? I even replaced the freakin fuse for no reason!

This bike is making me feel dumb ( walking to get the matches ) very discouraged

And from 6.7v idling and 6.4v with the key off I checked 20 mins later and I'm at 4.22v

swizbee42 said:

I want to get it done so bad, ironically I put it away about 4 years ago after doing all the same stuff with no results, I think that's why it's so frustrating.

What do you need for the 12v conversion, I've read like 5 different ways to do it

Click to expand...

From what I understand, a CB350 stator, (i have a CL350) a 12v voltage regulator, (i have), and 12 volt bulbs, (i have).

I'm not really sure.

swizbee42 said:

And from 6.7v idling and 6.4v with the key off I checked 20 mins later and I'm at 4.22v

Click to expand...

Well there must be something drawing power w key off.

You need to find it and make the repair before going any further.

You need to use your meter and trace through harness following schematic.

trek97 said:

Well there must be something drawing power w key off.

You need to find it and make the repair before going any further.

You need to use your meter and trace through harness following schematic.

Click to expand...

This! Going to 12 volt system is not going to fix a parasitic ground problem. The bike is simple enough that it shouldn't take over 10-15 minutes to find the problem.

WhyNot said:

From what I understand, a CB350 stator, (i have a CL350) a 12v voltage regulator, (i have), and 12 volt bulbs, (i have).

I'm not really sure.

Click to expand...

Does it specifically have to be a cb350 stator? I have a good line on a cl175 stator that I'll just pull the trigger on if it works

swizbee42 said:

Does it specifically have to be a cb350 stator? I have a good line on a cl175 stator that I'll just pull the trigger on if it works

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I'm not sure, just that it said a CB350 stator was a direct bolt in.

I should have tried it when I had the engine tore down last week.

Disconnect your battery ground cable. Put one side of multimeter to the negative post on battery, and the other to the actual ground cable. Set it to volts. It should read -X.XX. Unplug components one at a time (and then plug them back in) until that draw stops.