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Discussion Starter · #1 ·
So that's the motorcycle. I've put 1250+ miles on it since I got it two years ago. It hasn't run reliably for a year. I have discovered that troubleshooting an ignition with a kickstart is a strange form of torture.

I have rebuilt most of the motorcycle several times at this point. I tried an aftermarket cylinder (when I got a ring kit) but saw no reason for it. Got an OEM ring kit and switched back to stock.

I have replaced most of the electrical components on the bike. They all went one or two at a time. Ignition coil was easy, but components like the CDI unit are a mystery to me. A lot of parts I got from China, Taiwan and northern Europe. After the fact-- they're all cheap junk imo.

I have fuel, I have gas and my carb is clean as a whistle. I have a spark when I kick, but she rarely starts and when it does-- fights for the right to die.:madd:


So I have a last ditch plan and I was hoping someone here could tell me if I'm about to waste 500-600 bucks. (Blue book value on a 1985 Kawasaki cb125s is less than $900. Obviously I don't care about how much my motorcycle is worth to SOMEONE ELSE. I want it to start first kick like it should, period.)

New plan-- Honda wiring harness from a 2015 125cc dirt bike.

Module is $250! (Aftermarket ones were $10-20.) New OEM Coil, New OEM Regulator/rectifier and brand new wiring harness.

The 1985 cb125s has no starter. All the new harnesses have one.

Can I parts swap this $500+ electrical system to resurrect my motorcycle? (I'm ready to try it, but I'm looking for a nudge.)

Thank you for your time and consideration. :cool:
 

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Discussion Starter · #4 ·
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I'm new to posting on forums, but pictures are usually fun. Hopefully they came up.

This is what I'm working with.
 

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and my carb is clean as a whistle.
You don't REALLY know that, since the critical parts are small passages that you can't really SEE.

So....should you blindly continue on the assumption that there really is an electrical problem ? NO !!

Will it run any better with the choke partly ON ?
When it starts, if you let it warm up does it do any better ?
Do you have a stock air filter in place when testing ?

I think you would be MUCH better off to guess at a carb problem.
And then start with a healthy dose of Berrymans B12 Chemtool in the gas and a couple of test runs over a couple of days.
After that, a new carb might be in order.

The odds that you will fix anything by replacing the harness are very small.
But the odds that you will create a second problem while doing that are not so small.
 

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Discussion Starter · #6 · (Edited)
In the past, the engine is more likely to start with the choke partly on. I used to get it to idle but I haven't recently.
(The knot that forms in my calf from one day of troubleshooting usually lasts THREE :-/)

When it starts I generally need to add throttle to keep it running. If it runs long enough to get warm-- it will not start again easily.
(Last time I rode 3 miles was a year ago. It started like a champ and I thought I was golden. Stalled as I pulled into the lot.
I spent 20 minutes there doing business. Got back to the bike and it took 15 minutes of hard kicking (might have even flooded it and waited for it to clear) before I got it started.)

It used to do 55mph 4th gear and 65-70mph in 5th. Now (for over a year) it does 45-55 in 4th gear and 45-48 in 5th gear.

The only way I have gotten it started over the past year is a WICKED HARD KICK. I know I shouldn't have to kick so hard,
but it works-- eventually. IF it had an electric starter I feel like I could get it started reliably-- though it would still run just as poorly.
I HAVE gotten it started on a second kick while it was almost starting from the first. (I'm glad the compression is so low, or I'd have a broken ankle from backswings.)

--I'm not looking to add a starter, that was just a comment on my experience kick starting.--

I have never touched points. I don't know if that could be something, though the bike has less than 2500 original miles on it. (It was about 1200 when I got it, 2500 now.)

When I got it two years ago it wasn't registered for over 20 years. Started first kick, but everything rubber was shot.

I re-built the bottom half of the original carb. Replacement carbs have no accelerator pump, so I had decided to keep the original.
I have run wires and carb cleaner through every part I can. Long horizontal tubes don't take well to wires, but carb cleaner seems to flow with compressed air assistance.

I would definitely be willing to swap a carburetor, if that's my likely culprit.

I'd be happy to try "Berrymans B12 Chemtool" but without the ability to start / keep the bike running reliably-- that might not work even if it should.

Thank you for the response and I hope my info isn't too messy or irrelevant.
 

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Does this bike have a battery ?
If so, please tell me you have put in a new one......changed up fully.

And for the second time, do you have a stock air box and filter on it ?

You can test for fuel problems to some degree by squirting a LITTLE starting fluid or propane into the intake to see if that keeps it running better.
 

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Discussion Starter · #8 ·
The motorcycle will only start with a FULLY charged battery. 12.5-13volts or it just won't happen. I always charge it to full before trying to start the bike. (It is a new battery. I have two, used to swap them in the A.M. for a full charge before work.)

Yes it has the stock air box and air filter. (It is missing the CB125S body kit cover, but I believe it is aesthetic.) It also has two wire mesh (filters?) that sandwich the (cloth?) filter.

It had no air filter in it when I got it. First thing I did was buy an air filter. I didn't want to risk damaging anything with debris.

Starter fluid is really hit-or-miss. When I pull the throttle the accelerator pump literally squirts a stream of gas into the combustion chamber. Whenever I do get it started I usually try for a bit, let it sit for 5 minutes and then it has a "good" chance to start.

I've heard a bare bones bike like this should start with the kick without a battery, but I never could. Not even when it was running well.
 

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If you have never touched the points they may be pitted/dirty and or worn out....age related not mileage. The condenser/capacitor....same thing... may be toast and this allows the points to arc making it very difficult to almost impossible to start. A kick start bike will need to have a very big fat blue spark and poor points condition will rob the power available to the plugs. the timing and points gap need to be spot on too.

You mention a CDI unit and these do not use points...basically you have a capacitor and this is charged up by the alternator. A signal generator....magnet passing a coil...is used to determine when the cdi unit is to be discharged...a few degrees prior to TDC and this is what sends the power to the plug via a low inductance coil.

Wikipedia is a great source of info for CDI ignition systems.

You also say the engine fails to pull as well as it used to and that all the rubber parts were replaced. I might suggest ER is on track with the carb not being as clean as you suspect due to tiny rubber particles in some or all of the circuits...in particular the idle circuit...thus the hard to start and keep running issue.

I would be looking at pulling the carb apart again and using compressed air to clear the jets...wire is not a good option as it can damage the tiny soft brass jets and openings, carbs are made of very soft metal easily damaged or more specifically set passages can be enlarged. Sonic cleaning is another option which shouldn't be too expensive.

I would also be checking the fuel supply hoses for crumbling material, the tank venting system and any vacuum lines for security and condition.

One thing you have not mentioned is any fuel filters...if the tank filter is original then it will almost certainly be clogged up, the fuel tank itself may be crusted up with 31 years of crud too.

I suggest these points be checked out before any more money is spent on the machine.


Good luck
 

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Starter fluid is really hit-or-miss. When I pull the throttle the accelerator pump literally squirts a stream of gas into the combustion chamber. Whenever I do get it started I usually try for a bit, let it sit for 5 minutes and then it has a "good" chance to start.
This might mean that your starting "technique" is off a bit and causing a partial flooding condition.
Put the choke full ON and do not touch the throttle.
If it doesn't sputter by the second kick, move the choke back to half.

I still think you need to run some B12 through with the gas.
And you need to check the charging voltage while the bike is running.
If it really has a CDI, it will NOT start and maybe not run at all if a healthy battery is not present.

And I assume that you have replaced the spark plug at least once ??
I had an S90 and just about killed myself kicking it when the plug shorted out.
 

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Discussion Starter · #11 ·
ER-- THANK YOU for the solid starting technique. (Also, yes new plug.)
I have two stihl chainsaws and I run them properly.
When it comes to the motorcycle I kick and pump like a madman for no good reason.
I'm baffled that I've utilized no technique what-so-ever while kickstarting a motorcycle.... (I blame frustration.)

Aussie Steve-- "You mention a CDI unit and these do not use points..." Wow. And thanks for the wiki selection.
(You salvaged a piece of my sanity I had previously left for dead.)

I have the user manual-- been wrenching on this bike for two years now. Troubleshot so many problems I've literally lost track of them.

I replaced the CDI unit when it went bad-- and my bike ran like a CHAMP!
I was lulled for about a month and I thought I would never have problems again-- but then it became difficult or impossible to kick start.

The regulator/rectifier went. That was the last thing to go bad, or maybe the last thing to fully die.

I heard that short trips drain a motorcycles battery-- so I tried to blame it on that.
The reality is, my batteries NEVER recharged while riding. That's why I had two new batteries to swap daily.

It's my understanding that this motorcycle (Honda 1985 cb125s) was made in the years that manufacturers switched from 6volt to 12volt batteries.

I have not found the right regulator/rectifier replacement pre-wired for my motorcycle.
I have a hunch that the wiring configuration is obsolete-- which is why I'd like to replace the whole harness with an updated one.
(After further looking at the 125 dirt bike harnesses, they seem to lack wiring for a horn and lights at the very least.)


The original regulator/rectifier has 6 wires. It's a female six that plugs into the harnesses male 6. I have a wiring diagram somewhere and all of them seem to be called for...
The only replacements I can find are 5 prong (seemingly for motorcycles) and 4 prong (seemingly for dirt bikes.)

The bike didn't work right with the 5 prong. I tested resistances between the prongs and did my best to rewire a regulator/rectifier.
(It may seem like a bad idea, but after 6+months of no motorcycle I decided to experiment. Learning is why I bought the bike.)

That's the last time I got the bike to start-- but it was difficult. It idled with partial throttle and I rode in circles for a few minutes.
But once it got warm the bike died and wouldn't start.

Please forgive me for poorly presented information. This project has left me scrambled. You've both helped me already and I appreciate it!

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The first picture is the original reg/rec leaning against an aftermarket one.

Second picture is the bike's electrical system as it is now.
The ignition coil was the first thing to go bad-- new one was smaller, have it grounded on one side. Bike worked great then.
CDI unit worked like a charm. Went from not starting to starting again-- but it was never easy to start after this point.
Reg/Rect (with jumbled wires) replacement is the black box on the left.

The bike ran great for 1,000 miles after I replaced all the rubber and cleaned the carb and fuel tank.
I cleaned the fuel filter when I first got the bike. No rust inside the tank.
The fuel filter is only used when you manually switch to reserve. It's just a wire mesh.
There is no fuel filter directly from the tank to the carb. I could add an in-line if I wanted to, but that's not stock.

Thanks again for all the help.
 

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Aussie Steve-- "You mention a CDI unit and these do not use points..." Wow. And thanks for the wiki selection.
(You salvaged a piece of my sanity I had previously left for dead.)
CDI conversions often DO use the points......but not as originally designed.
They just provide a low current timing signal. They won't "burn" but can get dirty.
 

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Climber ;

Are you still here ? .

Did you ever get it sorted out ? .

If it started easily and ran great after replacing the CDI box, I'd begin there .

The alternator rotor has permanent magnets that over time collect ferrous SWARF that causes the CDI pickup to not 'see' them well, easy to clean with clean paper towels or napkins .

None of your pictures show .

I'm interested because I went through the same mess with my 1984 CB125S, I know it's a worthless bike but it's light weight and dead easy to flick through the twisties (beware of this !) .

I've dumped WAAAAAYY to much money into mine but it now runs AS-NEW so I'm working on the cosmetics .

Where are you located ? .
 
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