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Hi Ben, we see film of "third world" news, c90' with a kid on the handlebars, I kid standing on the footpegs, dad riding, mum pillion with a baby in her arms, and a bed on the carrier. C90's are a very underestimated bike. In the UK is a bike( or car ) cannot do 110 mph it's considered *#@p. I am not one of those people.

Cheapo infra red thermometers are great, carbs get cold equally ?

Carb needles, the ones in the slide, bottom notch is richest, top notch us weakest, but main jet will only pass max fuel relative to hole size...

Peg spanner needed to strip engine ideally....

Did you say that thrust washer was missing ?

Head bearings, good idea if done properly. More modern Honda's have ball race cam/head bearings.


Back later, sun shining and shopping trip to do.

Ps, just use bike below vibration period, don't blow it up.

Check CMSNL, clutch held on via circlip ?

Peg spanner nut not badly chewed up ?

Have a good day and stay safe out there.....

Oh, no further ign advance beyond 4 to 5 k rpm.....normal.
 

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Hi Ben, I worked on one of those a few years ago here in Bandung, West Java. I have PDF manual if you want me to email a copy to you?
The one I worked had been converted to CDI but still used the original auto advance mechanism, I can't see how yours can auto advance with the pick-up on the crankshaft.
The one I worked on was pretty bad, I had to put in 16 heli-coils, replacing the cut up pieces of a coca cola can, plus lots of other work.
 

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Discussion Starter · #43 ·
Hi Ben, I worked on one of those a few years ago here in Bandung, West Java. I have PDF manual if you want me to email a copy to you?
The one I worked had been converted to CDI but still used the original auto advance mechanism, I can't see how yours can auto advance with the pick-up on the crankshaft.
The one I worked on was pretty bad, I had to put in 16 heli-coils, replacing the cut up pieces of a coca cola can, plus lots of other work.
Hi there.

A fellow biker from Indonesia! Thanks for chiming in.

The cut-up coke can is the exact thing what I was talking about. Here shops would take a hammer or a grinder to anything just to make a fit - before opening up a manual.

Speaking of manuals, I have two and I believe you’d be sending me one of these? If you have another one please let me know.
These are the ones I have:

Shop Manual Honda 125-175 CB/CL
Service Manual Honda CB125-160

I believe my issue will be the crankshaft or other missing items like that thrust washer mentioned here. I don’t know if it’s on mine, can’t remember and haven’t taken any photos :(

good day,
Ben
 

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Discussion Starter · #45 ·
Ah, you have the same as me.

Keep us updated with your progress.

Whereabouts in Lombok are you? I may be touring Bali & Lombok Dec - Jan, I'll give you shout if I'm over.
I am in Senggigi - Lombok Barat. I’ll be in Nusa Penida from Dec 30-Jan 2 then Bali until Jan 5.
we can meet in Lombok or Bali. If I manage to get the bike to drive better, I’ll use that for the trip :)
 

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Discussion Starter · #46 ·
Hi Ben, we see film of "third world" news, c90' with a kid on the handlebars, I kid standing on the footpegs, dad riding, mum pillion with a baby in her arms, and a bed on the carrier. C90's are a very underestimated bike. In the UK is a bike( or car ) cannot do 110 mph it's considered *#@p. I am not one of those people.

Cheapo infra red thermometers are great, carbs get cold equally ?

Carb needles, the ones in the slide, bottom notch is richest, top notch us weakest, but main jet will only pass max fuel relative to hole size...

Peg spanner needed to strip engine ideally....

Did you say that thrust washer was missing ?

Peg spanner nut not badly chewed up ?

Oh, no further ign advance beyond 4 to 5 k rpm.....normal.
Thanks again for the info. Not a lot of C90's here but definitely a lot of C70's. I know because if I turn my head 90 degrees to the right I see 3 :) I have 2 C70's and a C100. I love these old bebek's - as they call them here. Bebek means Duck in Indonesian. Oh and I also see an old rusty vespa super 150...

Back on topic! Infra thermometer - got it. Will get one.

Good - so if no advance over 4-5K then my bike is all set when it comes to the ignition.

I don't remember the thrust washer. I hope it's there, don't want to open the engine now. I had the engine opened a month ago but foolishly I did not take any photos.
I do have a photo of the crankshaft I have in Japan and that is showing the thrust washer so once I get that over here I'll be good to go. I also see from my photos that I have an extra fuel pump / the chain tensioning mechanism and a clutch basket! Good to have these spare parts, hard to find them these days.

Peg spanner nut wasn't too bad if I remember correctly but again, I didn't take photos. I remember being able to open it without an issue.

So now carb stuff! Again, I am running Honda S90 carbs, two of them. They are repro but seem to work pretty well.

Sympthoms I am having. Maybe someone with more knowledge can guide me.
Bike idles well both with and without the air filter.
I manage to adjust the air screws finding the highest idle so I think we are good with that.

The issues I am having:

WITH AIR FILTER:
Bike idles and runs fine but at Wide Open Throttle (WOT) it bogs down and jerks - doesn't rev out. If I let the gas back a little it'll pick right up and run.

WITHOUT AIR FILTER:
Bike idles and runs fine even at WOT. However, if I have the bike on stand and I pull full throttle from nil straight away - the bike dies. So if I apply gas suddenly, the bike bogs down and dies. If I pull throttle a little gentler - it revs up nicely.
This is telling me that the bike runs rich - or perhaps I am wrong? I don't have different jets available - the only thing I can do is to change the position of the needle? Which way I'd go?

Plugs look good both with or without air filter.

Any help much appreciated!
Ben
 

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Discussion Starter · #47 ·
The one I worked had been converted to CDI but still used the original auto advance mechanism, I can't see how yours can auto advance with the pick-up on the crankshaft.
This one has no advancer at all - it is all removed. The CDI unit (which is a computer) does it's own advance based on the RPM. It reads the sensor on every crank rotation so it knows exactly how fast the crank is turning. Smart device but honestly I'd prefer to have it back to points which I'll do one day.

Where was your pickup if not on the crankshaft of flywheel? If on the camshaft, you'd need to have two pickups - one for left and one for right cylinder. For one camshaft rotation the crankshaft rotates twice.
 

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It was on the camshaft so two required, it only had one and the owner was complaining about the lack of power..... The left cylinder wasn't firing at all, I put on another pick up and both were firing. The owner was really shocked with the bike's increased power.:)
 

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Discussion Starter · #49 ·
It was on the camshaft so two required, it only had one and the owner was complaining about the lack of power..... The left cylinder wasn't firing at all, I put on another pick up and both were firing. The owner was really shocked with the bike's increased power.:)
Jesus :) that sounds funny.

My bike fires both plugs at the same time but as only one cylinder has compressed fuel on top of it, the other one ends up being a blank spark in the smoke (exhaust stroke)

So the CB125K3 is not your personal bike?
 

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It's good that a "local" has seen this thread, even better that he has the same bike.

The original points ignition centrifugal advance unit has two cams, but one set of points. This means a wasted spark system delivering a spark to both plugs for every revolution of the crankshaft. This you know.

As your bike is suffering from had vibration, and quite worn, and you are sourcing spare parts, being where you are etc., I feel I would just ride the bike avoiding the bad vibration period, IE riding the bike below 5 k revs or so.

You don't want any internal parts smashing Thier way to the outside world.

When you convert back to points ignition, you could use the points system to trigger your cdi system but the signal may need some cleaning up electronically.

There is room in the points ignition "space" for an electronic trigger system, but that's for after.....

Jet needles, start rich.....

You have a strobe timing light, any loss of flash /spark at bogging down on stand ?

It would be worth getting 4 red neon plug caps that flash when ht passes thru them. They fit between the spark plug and bikes plug caps but you may have to make an adapter.

They can be used when riding and can be seen, particularly at night. They are an inexpensive bit of kit and really usefull for ignition problem diagnosis.

They can rule out( or in ) an ignition problem.

Research " hall effect" sensors.

Research the system your cdi unit comes from, a battery powered cdi system only using the crank sensor for engine speed ?

Arduino micro processors are very versatile, there is loads of free info out there for these.

A friend is in the process of making his own engine management system using Arduino.

Stay safe out there...
 

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Discussion Starter · #51 ·
It's good that a "local" has seen this thread, even better that he has the same bike.

The original points ignition centrifugal advance unit has two cams, but one set of points. This means a wasted spark system delivering a spark to both plugs for every revolution of the crankshaft. This you know.

As your bike is suffering from had vibration, and quite worn, and you are sourcing spare parts, being where you are etc., I feel I would just ride the bike avoiding the bad vibration period, IE riding the bike below 5 k revs or so.

You don't want any internal parts smashing Thier way to the outside world.

When you convert back to points ignition, you could use the points system to trigger your cdi system but the signal may need some cleaning up electronically.

There is room in the points ignition "space" for an electronic trigger system, but that's for after.....

Jet needles, start rich.....

You have a strobe timing light, any loss of flash /spark at bogging down on stand ?

It would be worth getting 4 red neon plug caps that flash when ht passes thru them. They fit between the spark plug and bikes plug caps but you may have to make an adapter.

They can be used when riding and can be seen, particularly at night. They are an inexpensive bit of kit and really usefull for ignition problem diagnosis.

They can rule out( or in ) an ignition problem.

Research " hall effect" sensors.

Research the system your cdi unit comes from, a battery powered cdi system only using the crank sensor for engine speed ?

Arduino micro processors are very versatile, there is loads of free info out there for these.

A friend is in the process of making his own engine management system using Arduino.

Stay safe out there...
Thanks for your points. Interesting on the LEDs. Will look into it.
Also nice to learn about points / CDI hybrid.

Jet needles, start rich.....
What do you mean here? My setup is rich and I should lower the needle to restrict fuel?

You have a strobe timing light, any loss of flash /spark at bogging down on stand ?
Will check this tomorrow. Good idea!
 

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Led's, neon plug caps that flash as HT passes thru them from the bikes own plug caps to the bikes own spark plug.

They are not bling but a real world ht check, no flash no HT no spark.
I would be lost without them mine are a good 20 years old. I loned them to someone and it took 2 years of hassle to get them back. Don't lone out your tools !

I use them on any engine for a quick, safe and pretty positive HT test.
You can see them when riding your bike so the system is under real world conditions and loads.

Hall effect, ir light source and sensor as found in vidio players, and other triggering/signal techniques like a rotating magnet.

There will be a way that suits, even transistor assisted points ignition, but that system is subject to the usual points ignition problems, apart from actual points contact wear due to very much reduced switching load.

Arduino, there is loads and loads of stuff out there for these, probably a ready made system schematic and program. These devices are programmable so ideal, and not over expensive.

The program language is English, so no hexadecimal or the hidiouse machine code.

If you have done even simple basic basic programming, or turbo Pascal to mention two, you will some pick it up.
 

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Discussion Starter · #53 ·
Led's, neon plug caps that flash as HT passes thru them from the bikes own plug caps to the bikes own spark plug.

They are not bling but a real world ht check, no flash no HT no spark.
I would be lost without them mine are a good 20 years old. I loned them to someone and it took 2 years of hassle to get them back. Don't lone out your tools !

I use them on any engine for a quick, safe and pretty positive HT test.
You can see them when riding your bike so the system is under real world conditions and loads.

Hall effect, ir light source and sensor as found in vidio players, and other triggering/signal techniques like a rotating magnet.

There will be a way that suits, even transistor assisted points ignition, but that system is subject to the usual points ignition problems, apart from actual points contact wear due to very much reduced switching load.

Arduino, there is loads and loads of stuff out there for these, probably a ready made system schematic and program. These devices are programmable so ideal, and not over expensive.

The program language is English, so no hexadecimal or the hidiouse machine code.

If you have done even simple basic basic programming, or turbo Pascal to mention two, you will some pick it up.
Thanks for the information - I am ordering those plug caps as we speak. Sounds like a nice idea for troubleshooting.

What about the carb question? Is there anything I should do with the needle jet's position?

Thanks again,
Ben
 

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Clip in needle bottom groove which is the richest position to start process, make sure air filters sound, air hose to carb sound, air to head sound, no air leaks.

Usually but not always the fuel jets will only go in one hole. Float hieght/fuel level correct.

Post a picture of inside of float chamber, float and needles valve that regulates fuel into the carbs.

It would be good to do a fuel flow test front tank to establish free fuel flow, for say two litres, to prove fuel does not " hang".

If you know float hieght, make an accurate as you can float gauge, or, when picture seen, determine fuel level test possibility.

It probably is via carb float chamber drain screw outlet and clear plastic pipe. You may have already done this.

Balancing carb slides can be done by "ear", vision, probe or vacuum gauge if the head had the test points usually blanked off by a small X head screws.

You could make an air flow meter to compare carb to carb. The ir thermometer gun can test heat and cold, so exhaust pipes equal temp hot and carbs equal temp cold.

Stuff can be made from empty pop bottles, tubing , lightly sprung loaded or gravity controlled flaps, even water as an indicator. Just make sure water cannot, that's cannot be ingested by the engine..

Check for air leaks using wd40 spray or similar, just don't set the bike on fire !
Research a manometer.

I know you are out in the sticks but also know you are inventive and resourcefully and can make stuff from materials we throw away, we need to recycle much more than we do !
 

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Jesus :) that sounds funny.

My bike fires both plugs at the same time but as only one cylinder has compressed fuel on top of it, the other one ends up being a blank spark in the smoke (exhaust stroke)

So the CB125K3 is not your personal bike?
Unfortunately, not my bike, I was just working on it. The owner sold it after getting back from being repaired.
No Honda's in my hobby workshop at the moment. I have a 1966 BSA A65 ready to be shipped to Ubud, Bali, a 1957 BMW R26 that came in this week and 1961 Austin Mini. The Mini is almost finished, just need to tidy up the wiring.
 

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Hi Colv, it's good Ben has a "local" to help and bounce ideas about with...mini, a proper mini !

Bet you been having fun with that, real fun with the clutch and engine removal/refitting eh 😎..

Sounds like you have a nice and equipped workshop.
 

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Hi Colv, it's good Ben has a "local" to help and bounce ideas about with...mini, a proper mini !

Bet you been having fun with that, real fun with the clutch and engine removal/refitting eh 😎..

Sounds like you have a nice and equipped workshop.
Hi Drydreamer, you're right, it's been most enjoyable working on the mini, last time i worked on one of these was about 35 years ago in the UK.
Not had to remove the engine, a 1275cc SPI had been fitted a few years ago. The owner still has the original 850cc engine. I've fitted a new rear subframe, radius arm bushes, all the rubber suspension cones, brakes, ball joints etc, etc.
It runs and drives really nice, I have another one to fix when this one is finished :)
 

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Discussion Starter · #58 ·
Clip in needle bottom groove which is the richest position to start process, make sure air filters sound, air hose to carb sound, air to head sound, no air leaks.

Usually but not always the fuel jets will only go in one hole. Float hieght/fuel level correct.

Post a picture of inside of float chamber, float and needles valve that regulates fuel into the carbs.

It would be good to do a fuel flow test front tank to establish free fuel flow, for say two litres, to prove fuel does not " hang".

If you know float hieght, make an accurate as you can float gauge, or, when picture seen, determine fuel level test possibility.

It probably is via carb float chamber drain screw outlet and clear plastic pipe. You may have already done this.

Balancing carb slides can be done by "ear", vision, probe or vacuum gauge if the head had the test points usually blanked off by a small X head screws.

You could make an air flow meter to compare carb to carb. The ir thermometer gun can test heat and cold, so exhaust pipes equal temp hot and carbs equal temp cold.

Stuff can be made from empty pop bottles, tubing , lightly sprung loaded or gravity controlled flaps, even water as an indicator. Just make sure water cannot, that's cannot be ingested by the engine..

Check for air leaks using wd40 spray or similar, just don't set the bike on fire !
Research a manometer.

I know you are out in the sticks but also know you are inventive and resourcefully and can make stuff from materials we throw away, we need to recycle much more than we do !
Thanks again for all the suggestions.

I believe the air screws and the butterflies are now in full synch. Bike starts very easily with the push of the button and idles very nice. Even after a long ride with engine hot, bike idles identically to when it was still just warming up.

My intake manifolds don't have the testing screw but a quick look on the internet reveals the manifolds on my bike are handmade / reproduction pieces. Just placed the original manifolds (along with carbs) on my watch list at a Japanese auction!

This is what I did today:

  • Removed tank - placed on workbench (aka small handmade bamboo table I have) and opened the petcock - watching the fuel emptying into a bottle nicely. All looked good to me with the flow. Removed the petcock, checked for debris and found none. Reinstalled petcock and tank went back on the back.
  • Drained the fuel from both carbs via the drain plug to see how much was there - looked sufficient to me. The floats are also good - tested them when cleaning the carbs last week.
  • With the drain plugs removed, I opened the petcock to see how much fuel flows through the carbs. I assume this is what you meant when you asked me to test fuel flow. Both looked good to me but I am no expert so will wait for your opinion.
  • Tested the sparks with the timing light to see if I am detecting any sparks while I agressively apply WOT from idle and bike dies. I did see the light blinking.

I recorded 3 videos which I stiched together showing the left / right carbs' flows and the left sparks flashing light while killing the bike pulling a suddent WOT. The right one is identical so did not want to make the video any longer.

iMovie butchered the video while stiching the 3 together for youtube - a bit missing from the Top and Bottom but I hope you can still see what is happening clearly.

Video below:
Honda CB125K3 Carb fuel flow and spark testing

Please let me know what you guys think. You'll hear a couple of missfires while testing with the timing light, it happens sometimes with the bike cold. It was totally cold when testing.

Thanks,
Ben
 

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Discussion Starter · #59 ·
Unfortunately, not my bike, I was just working on it. The owner sold it after getting back from being repaired.
No Honda's in my hobby workshop at the moment. I have a 1966 BSA A65 ready to be shipped to Ubud, Bali, a 1957 BMW R26 that came in this week and 1961 Austin Mini. The Mini is almost finished, just need to tidy up the wiring.
Oh that's too bad, I was almost thinking we can take some nice photos in Lombok with the two twins while you are here.
The BSA is something I'd really like to once own - but first a Honda CB750. Already planning on letting my left kidney go for that one.

Sounds like you have a fun workshop going there. I am building a small garage here in Lombok also but it'll be for private use only - and for friends. Won't be ready by January I am afraid though...


Ben
 
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