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27 Posts
Discussion Starter · #1 ·
Dear all,

New to the forum, please take it lightly on me. Also new to twins..

I live In Indonesia (Lombok) and got this fantastic twin as my first real bike. Have a few cubs etc…

i had the bike rebuilt, new pistons and all looks ok with the build.
the problem I have is that over 5,000RPM the engine starts shaking and making a little noise - hard to tell from where but I suspect the top.
Here there aren’t many bikes that are left original and this one isn’t any different. It has aftermarket carburetors and the pistons are from a C700 super Cub - brand new and block bored to match. No shop here can bore below 47mm so had no choice but to go with these type of pistons.
The bike was also converted to CDI before I got it, there is a little metal tab welded to the crankshaft just below the flywheel which actuates a pickup coil. The timing was off but I corrected it using a timing light - moved the position of the pickup coil. Timing should be ok, cam chain as well, valve gaps are good.
compression is spot on and the bike starts on one kick in the morning, pulls strong, the only issue is the vibration.
Any advice would be very welcome.
I am basically on my own with this as there aren’t other twin bikes here on the island and not one garage knows how to handle it


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27 Posts
Discussion Starter · #6 ·
Hello there, thanks a lot for your answers and here is a reply to your questions.

model: CB125K3 - 1969. I am aware of CMSNL but as so many of the parts are non-original, it is sometimes hard to work with it.

C700 piston - it’s basically a supercub C70 but a newer version. The C70 pistons until 1980 had a dome shaped crown and later models (here called C700) have a flatter crown. The piston size is otherwise the same, 47mm diameter. The original CB125K3 pistons were 44mm and here the shops can’t bore that small of a size.

The CDI does allow advancing and I saw this with the strobe light, however testing timing with the flywheel cover opened isn’t exactly easy. If I tilt the bike to the right and keep at at base RPM it’s kind of ok for about 15-30seconds, however as soon as I crank the RPM’s up, oil sprays Uncontrollably.

No shiny parts on the piston crown, there’s no touch of the valves.

valve gaps have not closed up, will recheck again today.

Is there a best way to synch the carburetors? I made sure air screws are identical in setting and also that the throttle bodies move at the same pattern on both sides.

I will try to take a video and upload.


27 Posts
Discussion Starter · #11 ·
I’ve created this video, best I can do. Would need 3 hands!

I am in 5th gear going from 60km/h to 80. I hear the noise and feel the vibration but granted on the video it isn’t really showing.
Maybe check the rear view mirror how the trees are blurry. Until 60 I see everything clear in the mirror and after that it starts shaking and things get blurry. Annoying at night with the lights from behind looking like bright dots going wild in the mirror.

I’ll reply to the other questions also later.

CB 125K3 60-80km/h vibration
Could you take a vidio from a bit further away please and at revs so the nouise/vibration can

27 Posts
Discussion Starter · #19 ·
Replying to your questions first:

What rpm is the vibration occuring ?

What sort of noise is it ?
Hard to describe, it just starts knocking a little - sunds like it is coming from the top. On the video it can't be detected at all!

Does it vibrate in every gear or just in top gear ?
Every gear - yes!

How is the rear wheel drive chain ?
All good and stock. Front 15T / Rear 47T. When I bought it the configuration was F14T / R40T but CMSNL tells me it should be 15/47. I got the right sprockets from Japan and installed them along with a new chain. It drives smooth but I found this stock configuration a little too short. At 70km/h I am already passed 6,000 RPM.

I assume stuff like tank rubbers are good and the tank is not touching the frame etc..

Plug gaps look a bit wide.
I checked and they are 0.7mm.

Colour looks a bit on the weak side.
Yes - motor runs a bit hot. Carbs are aftermarket and for a different model - this is what was suggested by a garage in Java saying this is what all Indonesian riders use once their original carb is tired. It is from another honda bike.

Left plug thread looks troublesome ?
Yes - very hard to access the left plug as it is deeply recessed.

How is that cylinders plug hole thread ?
Thread is good - new. I took the head to a shop and they remade the plug threads.

You have a plug hole thread cleaner/chaser ?
No I don't but can get one easily online. The plug sits first though...

Be extremely carefull with that plug hole...always start plugs into plug holes by hand...
Yes will do!

Picture of engine from a little further away, to show timing pointer on stator.....
The timing pointer is not there anymore, long story. In Indonesia most bikes are butchered. When this was converted to 12V and CDI ignition, they put a new coil in etc. Anyways I found TOP and market it on my video with a bent barb wire.

Just to clarify, cam chain is on left of engine ?
Yes it is.

To hear the noise at the vibration revs would be good.
I tried to record it but it wouldn't work. Engine sounds just fine on video :)

You sure it's not wheel vibration or exhaust system vibration ?
Yes pretty sure.

From memory handle bars are rubber bushed ?
No they are not. I am also not worried about a little vibration from the handle, it is just that the engine vibrates a lot after 5.5K and I am sure it should not be like this.

Another busy day for me so back much later...
Thank you for your time! Very valuable.

And to PoiPio's comment about crankshaft being out of balance, I think it is but maybe within tolerance? I tool a slowmotion video of it spinning so you can see how it goes out of true a little.

Video of crankshaft rotation slo-mo

And then a long overdue brief explanation of the bike.
I got it from Sumatera - another Indonesian island some 1000's of KM's away. Here in Lombok there isn't another Twin Honda from what I know, I've asked a lot of people.

When the bike was unloded from the truck in front of my house, I started it up and it ran really rough. I drove it around a few times but it was dreadful so I decided to have it rebuilt. As I find noone here in Lombok with skills, I sent the engine over in a crate to the island of Java where a so-called specialist had it rebuilt. The engine came back a month later and I had it installed in the already repainted and beautifully restored frame, just to find out it ran pretty much as poor as it did prior to sending it out.

This was the point when I decided I need to learn this on my own, I opened the engine and I found a lot of issues, parts missing (small bushes etc). I had a chance to visit Japan a few months ago and I bought a lot of second hand parts there for the bike which I then brought back to Lombok with me.
I got the bike together and it is now pretty much back to stock with all parts correctly installed. What is non-stock are the following:

CDI 12V ignition. (the coil around the flywheel is 12V / the pickup pulser is fastened underneath the left engine cover, the pickup metal tab is welded onto the crankshaft. I had this worked out pretty well i think after having played with it for weeks. I managed to get the position of the pickup to the perfect place and also got the length of the metal tab right. As you could see from the timing light test, timing is spot on now.

Pistons are from a Honda Supercub (C700) - 70cc each. Cylinder bored up to 47 or 48mm - forgot which.
Head gasket is unmodified but the piston doesn't reach as far up as it would come in contact with gasket.

Ignition coils - there are two of them, one left one right - the original had a single coil with 2 wires. Since the crankshaft in this bike is the 360degree type, both coils basically fire at the same time on every crank rotation but I find no issues with this as the piston that is not on the compression stroke will just ignore the spark - given there's no compressed fuel mixture there.

Other electronic bits, regulator-rectifier / winker relay / dynamo starter relay / battery / bulbs are all 12V but I think they are not relevant for my issue here.

The bike also overheats a little but that could still be due to the fact the new pistons only have 600KM's on them. I take it easy on the bike for now.

The bike starts with a single push of the starter button when cold, no need to play with the throttle at all. When warm, it won't start unless I give it a tiny little gas but then it starts right away.

I'll share a few photos in a second from my phone of the build - where you can see the weird crankshaft welded tab / the pickup and also the pistons in top position - not touching the gasket.

Thanks a lot again!

27 Posts
Discussion Starter · #20 · (Edited)
Crankshaft 12V convention pieces showing. The rag is there to prevent things from falling into the engine casing as I had the bike tilted on its right

Art Pattern Metal Fashion accessory Carmine

This is the piston setup in top position. The original pistons had a dome shape and would stick out from the cylinder and into the head. These are flat. I guess my compression is somewhat lower…

Automotive tire Wood Material property Gas Font

And a few other random build photos

Head taken apart and serviced.

Brick Font Building material Brickwork Cross

New valve seats and re-used old valves - they don't leak. I went through the hassle and grinded the valves into the new seats using the grinding compound.
Photo also shows how the plug threads were reworked. They were made smaller (as the original threads were beyond repair) and I now have to use a smaller plug. The original to be used is NKG D8HA and the one I now use is C7HSA I believe. It has a little different of a heat index but I think it should be fine? Tape is used to cover up all holes for the thread repair. I also loosened up the valve rockers so no valve would be open during the repair.

Automotive tire Wood Grey Audio equipment Loudspeaker

New valve seals added. On this bike only the Exhaust valves use seals so that's exactly what I've done. I could not get original CB125K3 seals so I am using C70 seals - they are identical (to the naked eye)

Hand Finger Wood Thumb Nail

The valve seals as seated on the exhaust ports.

Automotive tire Bicycle part Font Auto part Rim

I carefully adjusted all valves to the recommended 0.05mm gap.

Tableware Drinkware Dishware Coffee cup Cup

Pistons going in.

Plant Automotive tire Motor vehicle Houseplant Flowerpot

And at the end I used the timing light (once engine was in frame and running) to make sure the location of the pickup was right. I had to move it a few times....
I also checked compression and my cheapO gauge showed 51PSI for both sides... a compression which would of course render the engine useless if was true. My gauge is far from accurate I guess but the fact both sides showed the same value was reassuring.

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27 Posts
Discussion Starter · #23 ·
At what gear did you feel the vibes? I did feel them too but after my 1st service they were down. I observed them in 2nd gear mostly at 40kmph. 3rd at 40 to 50 it’s butter smooth. Rubbing sound at the rear? Might be some mud. I previously had a 2014 RE tb350 so it’s almost none vibes for me when compared 😅
At all gears and I am not hearing any sounds. It isn't chassies related but engine I am afraid :(

27 Posts
Discussion Starter · #24 ·
And back at your questions again - sorry for the delay.
I also updated my earlier photo section back a few posts with descriptions. Could you guys look at it again?

Only one vidio showing the tdc reference wire pointer ?
Here is the video showing the crank vibration - it is slow motion so should be ok to see how it is out of true. I have no idea if it is within tolerance or not....
Crankshaft out of true - slowmotion

And yes - the TDC hack is made of barb wire and I only slip it on when I check timing. Here on the slow motion video that piece is not there.

Seen your picture of the cdi crank position sensor......
Not a very elegant solution - was done before I got the bike....

So there is some "wobble" of the alternate rotor, but it's within spec ?
I have no idea how to tell... :(

How much of a wobble is it ?
I'd say a 1mm or 1.5mm tops? Not sure how to check this accurately, please see the slow motion video.

1mm or more ?
Yes at least 1...

Also some end float seen, in and out movement, how much is it please ?
I don't know how I could check this but I remember there was some some in-out movement when I assembled the engine. I'd say at least 1-2mm's but I can't recollect this clearly.

The rotor timing marks are a bit difficult to see in your vidio, but you may see them very clearly. You sure they are to spec and not over advancing ?
Yes the timing is now spot on. Hard to take a nice video of the flashing light...It isn't over advancing but then again, I didn't try past 3-4k RPM as the oil is spraying like crazy :) What I did see is as I apply the throttle, the advance mark moves closer and closer to TDC and at one point it reaches it and then stays there - won't go any futher.
So at idle RPM it is the "F" mark and as I go beyond the advance markers are moving closer and at around 2-2.5K (guess only) it reaches it and stays on - won't advance further even though I apply more throttle. Hope my silly explanation is somewhat understandable....

So no frame and cycle parts vibrating badly making a buzzing noise.
Nothing that I've noticed. I do feel the footpegs and the handle vibrating a little though... Nothing rattles.

The ign " bolt" welded to the crank may be an issue, adding or subtracting to imbalance, but it will have some effect.

As you know, it's mass may be small, but a 5k revs, it's "effective mass" may be considerable. What's done is done.

Yes I fully understand this but I think the flywheel being out of true would create an even more considerable vibration?

Do you have the old parts to convert it back to points ignition ?

No I don't but I started buying them and will eventually go back to points if I can't figure this out.

Cylinder head gasket protrusion into the combustion space may be/could cause an issue but you are confident the piston crowns do not make contact.

I'd like to believe so that I am confident :)

I wonder how the head gasket sealing ring is surviving it's "torture"....
I won't be able to tell unless I open the engine up. Hope they are ok! When I got the bike it already had a 47mm piston in it so was overbored and using a stock gasket. When I did the rebuild. I did not notice anything strange looking at the gasket.
Then I got a new block with a standard bore (with minor scratches) and pistons for it (0.25 over) - just to find out noone can bore the block for these small diameter pistons. The STD is 44mm so the one I wanted done was 44.25mm...

I went back to the block I got with the bike and got with the supercub pistons.

Thank you for all your help.
A quick update - I installed smaller carbs yesterday which are closer to the original in terms of specs and the bike runs better and doesn't lose power when hot. It is still hot though...
Raining now so can't test right away but when I had a chance to go for a longer run, I'll update back with plug colors etc.
Bike still vibrates of couse...

27 Posts
Discussion Starter · #30 ·
In-out looks normal. What is not are the rollers, the slop in the chain tension, and a crank gear tooth that looks more worn than the rest. So maybe it's noise not vibration? Tighten the cam chain see if it helps.
Maybe I forgot to say in the video, I slackened the chain on purpose to be able to display the in-out play. With chain tensioned the play is harder to display.

Glad the in-out looks ok. Did you see I can also move the crank up and down a bit? Maybe .5mm


27 Posts
Discussion Starter · #31 ·
Hi Ben, I will have a proper view later this evening, I must crack on with the car, due for its annual mot test very soon. An annual safety inspection.

Do you have Vernier gauge it can measure endfloat ?

If not even a long bolt and nut, to record difference between in and out. A know pitch and number of degrees but turns to show difference...

A bit noisey here so audio not heard, cam chain very slack...

Can you take a picture further back to show top and bottom of engine please ?

Some more chewed screws seen....back later, 3 hours of daylight left. Coffee break over, back to the grindstone...
Good luck with the car!

I can’t measure the in and out play but hopefully you see in the video. When you are in a quieter environment please watch again, I explain a few things in the video.

I just sealed the engine up with liquid gasket as I had a few leaks, don’t want to open it up again unless necessary? I’ll look for a photo from further away. Hope this will do?

Enjoy the coffee!
The chewed screws show the hard life of bikes in Indonesia - and the inexperienced service centers. I’ll have them replaced…


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27 Posts
Discussion Starter · #40 ·
Hello there!

Back with more replies - thanks a lot for taking your time in walking me through this challenge.
I drove the bike more and now have 1000km's on the new pistons which means I can (should be able to) push it harder, which I tried. The bike really vibrates at any RPM over 6000 - it isn't something I can pass and then evens out at all. It is just there from 6-10K - haven't gone beyond 10 as it feels like it'll fall apart under me.

So to your questions. The carb part will be interesting, maybe I can tweak things there. I heard with twin (or more) carburateours that need to be synched manually, the problem can often be that one piston is better fed than the other and this causes all kinds of vibrations etc. I already adjusted both carb butterflies to slide exactly at the same time and also made sure both carbs have the air screw at the exactly same position. I took the carbs apart and cleaned them, the jets are identical in both of them. The headers warm up evenly - tested this by holding on both headers at the same time for as long as I could after a cold start and I had to let both go at the same time. I did not want to wait while smoke rises from my palms...
The sound from both exhausts are the same.

Ok again - to your questions now:

Looking at a picture of that thrust control ring, "washer" , it doesn't look very thick. I wonder how worn that is, or is it missing perhaps ?

I checked for any photos that I might have during disassembly that shows that ring and the answer is no :( But the idea is very good and I'll make sure to check for this when I have the new crankshaft with me for which I'll need to open the engine. The crankshaft I bought it used but it is "used in Japan by a Japanese rider" which will without a doubt be a 100 times better than what I have here. Here a bike is the transportation for the whole family and every day. I can imagine this bike was lugging 4-5 kids on dirt roads etc... In Japan they drive on the weekend and change oil regularely - this is of course a stereotype but as I lived in both countries for years, I think I can bet on this being the case.

End float looks a bit excessive to me.
Up and down play, radial play, again looks excessive to me.

I was afraid of this. Nothing I can do until the new crankshaft is with me - which will be next year.

Definite "wobble" in alternater rotor, damaged by a 3 leg puller ?, It something bent ?

I think this is just because the crankshaft is out of true. Remember it was opened (and I don't know how many times) then re-pressed. The sprocket on the crankshaft is also positioned wrong by a few millimeters which means I can't get TOP on the camshaft when the piston is in TDC - the top position would be in between two chain links. Nothing I could do except to bore a larger opening on the camshaft's sprocket and turn it slightly to allow for the camshaft to be in true TOP position. It isn't 100% accurate I am sure but a lot better than before. I explained this in my video - but not sure if what I said made sense or if my accent was understandable :)

One of the cam sprocket bolts looks odd and I cannot see the O mark.

O mark is there as you've by now seen it on my video. The bolts are just normal bolts as I can't get the special ones here - so I used a grinder to make the heads thinner. On this bike by the way the two bolts are of different sizes, this is so you can't put the sprocket on in the wrong orientation. Pretty simple but very smart! The bike uses a 360 degree crankshaft so I think even if the sprocket went on the other way nothing would happen.

One of the final drive chain sprocket bolts look odd also, which can cause a problem.

Those were replaced since. Now they are the original Japanese bolts with the "8" stamped on their heads. Got them in Japan.

Is the cdi unit "Arduino" based ?

I don't know. It is from a Suzuki Shogun 110cc bike. I tried looking for information on what this bike is called internationally but I can't find anything.
I just checked for arduino and I see it's some fancy programmable unit. This is definitely not one that can be programmed so it is stock and has a limiter from what I understand. I know nothing about it otherwise but bike seems to advance just find and won't advance beyond the point that is marked on the flywheel. Not sure above 4000RPM - haven't yet tried. Once I get a hold of a secondary cover and be able to do this through a little hole.

Slow Motion video being a good idea
Yup - figured this out on my own. I just use my iPhone's camera and there is a slow-motion option. When you open the camera up - you can scroll left and right to choose between modes - there's photo / video / timelapse / slowmo etc. This slowmotion works fantastic!

Do the cam sprocket bolts faul the alloy cam sprocket cover ?
Not they don't. I can't hear any noice or see any scratches on the cover.

It's a bit risky running the engine with that cover off as it controls cam shaft end float !
I had no idea it can move and even when I tried yanking it, the thing would not move! Wish the crankshaft was the same :). This head is from Japan by the way, the one that came with the bike was a total disaster. It was used so extensively that the hole for the shaft must have become worn to the point where the bike wouldn't start. If it starts, it will be used. Service is normally only seeked when bike isn't moving anymore.
So the previous (or before that) owner had bearings fitted on both ends of the camshaft and bored the head out to accomodate for this. The bore and the bearing isn't an exact match so the camshaft had a rather large play in the head. This is no longer a problem, I am using one I got from Japan and it is like new!

Since you are going to the expense of getting a new unused crankshaft, which I hope is in a wooden box or similar, get new cam sprocket and chain and the cam sprocket bolts.

Yes will buy all these parts on my next trip.

How is the cam chain centre spreader, the large rubber wheel riding on the special bolt below the spark plug on the cylinder ?

Already replaced it to a new one. The one that came with the bike was half the size :(. As long as it works.... :)

It may be an idea to replace it anyway, along with the two rubber rollers/idlers/cam chain adjusters.
One roller I've already replaced and the other one is sitting and waiting for me in Japan.

Research CMSNL for that thrust washer and peg spanner to remove the primary drive gear...
I did look and understand what you mean by that washer and the odd gear that drives the clutch basket.
I don't understand what you mean above - you suggest I remove it and inspect it - hence the need for a peg spanner?

The carb slide needle, top, middle or bottom groove for the little clip ?
As mentioned above - here I think there is still work I can do. Nothing about the crankshaft play I can quickly change so the meantime would like everything else to be sorted so when I install the new crankshaft - thing would just start being perfect :)
The carbs are aftermarket but do resemble the ones that were originally on the bike. These are for the Honda S90 otherwise - and aftermarket so not the original Keihin. They do work quite good I think. They ran just fine before I fitted the airfilters and now with filtration, they bog down at WOT. From idle to 90% throttle all feels well, engine doesn't overheat and plugs look good. However, when I smal the throttle all the way, the bike starts to hesitate and jerk.
I assume it has to do with the air not mathing the fuel being supplied - given that I restricted the airflow with the filters?
What do you suggest? I can play with the needle but which way I go in this case? I assume down - to restrict fuel to match the restricted air flow?

You do have the air box/filters connected ?
See above...

Copper Head Gasket
Will do this when I take the bike apart to replace the crankshaft. Now the engine is fully sealed with gaskets and additional threebond liquid sealant and for the first time I don't have leaks :) Very proud!
Opening the engine is rather hard as the sealant holds it together, don't want to do this too often.

Thanks again! Much appreciated.

27 Posts
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,

27 Posts
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 :)

27 Posts
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:

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.

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!

27 Posts
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.

27 Posts
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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