1983 CB125TDC gone cold on me :O(

[lefty]

This morning, while tinkering about with the bike fitting new choke cable and tacho cable, I noticed that the left hand cylinder and exhaust (looking at engine from seated position) were cold compared to the right hand cylinder.

The downpipe and cylinder weren't exactly cold but I could comfortably hold my hand on them for a long time whereas the other cylinder and downpipe were too hot to touch for any length of time.

I'm assuming the choke mechanism may be at fault (as they are apparently prone for going t1ts up) or a duff spark plug (there does seem to be a little pop now and then on tick over).

I will be stripping the top end down pretty soon anyway as I noticed there doesn't appear to be proper gaskets on the top end, just red gloopy sh1t. While I'm in there I will do the tappets/camchain tension, oil 'filter' and check on the clutch plates as outlined by Teflon Mike in his excellent guides.

Then rebuild with fresh new gaskets and hopefully all will be fine and dandy

Anybody got any other suggestions for the cold cylinder?

I really do need to get a Haynes manual but can't seem to find one to download. May have to delve deep and buy one. Feck!



**UPDATE** our lass told me not to be a tight arse and said I had to buy a manual. One coming from fleabay

[Usher4566]

Mine is same I've got a post about my cd200 running on one .have you checked for spark on that cylinder .?if you get any joy can you let me no .?
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New cd200 benly owner

[lefty]

Took the bike out this morning to nip to the shop for supplies and both cylinders and downpipes got nice and hot

It's a busy weekend for me this week so won't get much chance to tinker but as soon as I can I will delve in with gusto to check for strong spark, look at choke mechanism etc......

I'll report back when I have some news.

[lefty]

Had a chance to play a little while this morning. Not had much chance to do owt cos of the bloomin rain and being at work

I've changed the spark plugs and had to get new leads as the old ones literally disintigrated when I tried removing them

She still runs the same: left hand cylinder cold compared to the right hand side.

One thing I have noticed today, there is a smell of unburnt petrol coming from the left hand exhaust. My useless sense of smell probably explains why I haven't noticed this before.

Took the bike out for a little blast and she pulls ok but has a flat spot around 5500-7000rpm. Not when gunning it but when held there over a sustained period. This just so happens to be at around 40mph in top gear.

When I got back home, both exhausts were hot.

What do you reckon, coil acting up?

Or could it be summat else?

Thanks in advance.

[Usher4566]

What couler are both plugs mate
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New cd200 benly owner

[timmy222]

Checking the left hand lobes on the camshaft, as sitting on the bike direction.
The engine had a habit of the left oil channel blocking and could wear one of the valve lobes down very quickly.
Hope it is not that for you though.

[lefty]

[lefty]

My top end gasket set arrived this morning from Riders Yeovil.

"Genuine Parts" it says on the packaging.

So why doesn't it say "Honda" anywhere then?

The only English writing on the packaging is the aforementioned "Genuine Parts" and "Made In China".

The rest is all gobbledigook.

Oh well, as long as it does the job

When it stops peeing it down long enough, I'll try swapping the coil for the left hand cylinder to see if that makes any difference and also have a go at the tappets.

Don't know when that will be as the weather doesn't seem to want to play ball

[lefty]

Had abrief dry spell this morning so decided to give it a go with the coil swap-over.

A previous owner of the bike has obviously decided to wage war on any damp/water ingress and very kindly coated everything (ok then, coil & wiring)with grease. YUKK!!

After wiping it all away and swapping the coils over I spun her over expecting (hoping) for the left hand cylinder to start and warm up and the right hand one to just go luke warm. A reversal of what was originally happening.

Nope, still the left hand cylinder that stays cold in relation to the right hand one and the smell of unburnt fuel from the exhaust pipe.

Well at least that means the actual coils themselves are ok.

I suppose the next thing to try would be the CDI units.

Does anybody know if they relate to the side of the bike they are on?

By that I mean does the left hand one (sat on bike looking down at them) control the ignition on the left hand cylinder?

I'll try swapping them over and see if that makes any difference to which cylinder warms up.

I'll keep you all informed as and when I actually get around to doing it. Missus, kids, dog,work and weather all seem to get priority over anything else.

[lefty]

As well as trying to fix me inkydators (see other thread) I tried swapping over the CDI units to see if that would make the right hand cylinder run cold.

Guess what?

It didn't

Looked at the choke mechanism and both seem to be operating as they should when using me knob on the handlebars. OO-ER missus

I'll take another stab at something else another day cos me inkydators needed looking at.

Any ideas what?

[Teflon-Mike]

Fault finding is a LOGICAL process of ilimination. But you are NOTR being very logical or methodical here, and its almost like you keep playing with the ignition system in the vein hope that 'some-how' you'll find and fix the problem by voodoo, and not have to take the engine to bits...

Have you taken the spark plugs out of the head and tested them against the fins to make sure both are sparking?

If so, you PROBABLY dont have nything wrong with your ignition system.... SO you dont carry on down THAT avenue of investigation until you have bottomed everything else, and it 'may' be a case of a weak spark.

>> These bikes are renowned for starting up on one pot, usually the right hand one.
>> They are also renowned for not delivering a particularly beefy spark on 'cranking'.

They have a 'self exited' ignition system, power to make sparks comes from the magneto, even though they have CDi amplifier modules, these are not amplified by battery volts, BUT unless you have good battery volts, the starter motor wont spin the mag over fast enough to power the spark-amps, and they can 'drop-out'.

>> Starter clutches are renowned for 'sticking'
>> Starter motors renowned for getting a bit tired.

Pulling the Mag cover off, you will find that the starter motor drives the crank shaft by a bicycle type 'freewheel' and chain behind the rotor.

The rotor comes off with I think its an M14 bolt screwed into the middle... but it probably wont.... none of mine ever have.... have to take them to a local M/C shop to press off with a high tonnage hydraulic press.... but I'll leave that one to you.

If you take the rotor off, you can slide the starter sprocket out of the back, and will see three rollers unning on three ramps pressed down the ramp by springs.... if they haven't popped out, which is the actual 'ratchet' or clutch mechanism... and its probably rather rusty.

Strip, clean and grease, and put it back together. While you are there, oil the chain.

If you cant get the rotor off, then work the sprocket back and forth to free up teh rollers and squib loads of cvhain lube behind and work into teh rollers... not 'great' but better than nothing.

Starter motor is a lovely thing; it is a biy DC motor with integral planetry reduction gear in teh nose, and it ALL comes apart.... if you can get the screws undone.

The motor's rotor shaft runs direct in the planet gears at one end, but in a bronze bush the other, while the brushes have snail clip springs to keep them bearing on the armature. They are NICE BIG carbon brushes, and a nice big, and THICK copper armature.

Remove brushes, clean all the old carbon dust and crap out, and polish the armature ring until the copper is bright. Strip the planetry gear, get rid of the old gloopy goo that was once grease, clean, regrease and re-assemble.

Putting it back on; pay attension to the four feet that are the earth connection, & make sure that the feet aren't furred up and that the mounting bosses aren't corroded or painted, creating a high resistance path, sapping cranking amps.

Starter 'feed' wire, make sure that is clean and the cable tight, and trace it back to the solenoid, which similarly is likely to benefit from being opened up (its held together with screws), drained of water or condensation it's inevitably full of, the contacts cleaned, and the actual actuator rod lubed.

NOW make sure you have a good, preferably 'new' battery, and its well charged...

Speed the engine will crank over on teh starter motor will seem IMENSE, and you will think it has lost all compression, for the difference it makes..... probably HAS lost a lot of compression, but we'll get to that in due course!

MAKE SURE YOUR STARTING SYSTEM IS IN GOOD ORDER.

Next: You have muttered about sooty plugs and muttered more about smell of unburned fuel.

HAVE you cleaned the carburettors?

If not DO SO.... BUT before you remove them.... PLEASE take the battery out and REMOVE THE AIR-BOXES.

Trying to wiggle the carbs out from between the engine and air box almost inevitable results in the mounting rubbers getting FUCKED... these parts are like hens teeth to get hold of in good condition, so unless you want MAJOR hassles.... what are you going to do before taking carbs off? Thats right, remove battery and air-boxes!

Upside down, remove float bowls, CAREFULY, dont ruin the heads on the three screws.

You then have the float, and the float needles that can be lifted out to expose the ide and main jets.

Float can be cleaned, float-needle removed and cleaned, float needle port carefully cleaned. You CANNOT adjust the float height on these carburettors.

The mian jet can be unscrewed from its emulsion tube, and cleaned seperately to the emulsion tube, that unscrews from the carb body. Idle jet is a single piece that unscrews.
BOTHE have small drillings around the sides of the emulsion tobe to allow air in to 'atomise' the fuel.

On badly 'laquered' emulsion tubes, these can easily be missed. Scrub with something not TOO abrasive, tooth-brush or nylon pot scourer, until you can see the holes, then make sure they are clean and clear through to the jet.

NOW, at the FRONT of the float bowl in the carb-body is the idle air screw. Little brass screw, with knerled end and slot for adjustment.

This has a thin needle on the end, and is in effect a VERY miniscule 'tap' and it controls the flow of AIR through a drilling in the carb-body, that feeds air into the emulsion tube chambers, and hence controls the 'basic' misture strength.

If this is damaged, or gummed up, you will NEVER get the carb to meter correctly.

If the drilling that feeds the air to the emulsion chambers is furred up or blocked, you will NEVER get the carburettor to meter correctly.

On the screw, though is a spring, and a rubber seal. So be careful when you take the screw out that these DO come out with teh screw.

If the seal doesn't HUNT for it in the hole, they do get stuck. But they can also break down, or go missing.

The mixture screw will need cleaning, the hole it sits in will need cleaning, and the carburettor body will need cleaning, and that drilling cleaned out. This is NOT a poke it with a bit of wire job! And best to get bodies ultra-sonically cleaned, though you can do well with pipe cleaners and cottom buds if the body isn't TOO far gone.

With a GOOD clean carb body, you can put it all back together.

Pay particular attension to the float mechanism when you re-assemble; they frequently 'jam'.

Pay even MORE attension when you fit the float bowl back on, and be SURE to tighten the screws up evenly, and NOT to over tioghten them.

Float-bowl needs to be square to 'seal' and over tightening can distort them and MAKE them leak.

Clean the slide and slide needle. Make sure slide needle is in the correct notch. From memory it is NOT the middle notch as you would normally presume, but circlip one notch up from middle.

Next, the idle air screw we mentioned, needs to be set to the book, which I believe is ALL the way in, then five 1/4 turns back out.

He-He: THIS is where you win having checked up that hole for the seal. Becouse if you have NOT got a seal in there, then 'all the way in' will probably be three full turns more than it should, and five 1/4 turns back out, wont be anywhere near the right mixture setting. WHICH so few people bother to consider, and just tighten that screw up as far as it will go ANYWAY... we dont want screws coming undone, now do we?

And I THINK, though book doesn't say, that 'In' is mix rich, and out leans it. This COULD be a 'lead' on your sooty plugs and petrol smell... but lets NOT jump to conclusions....

JUST - Clean carbs, set to factory settings!

OH, and when carbs are going back on, pay attension to the choke linkage and make sure that when choke 'off' both flaps ARE actually fully open, and that the Right hand flap isn't wobbling, left hand flap not partially closed, AND they are HELD by the choke cable.

THAT lot done, come back and tell us what the results are!

I suspect, you will almost certainly have low compression, WHICH will be the result of pitted inlet valve seat, probably worse on the Left Hand cylinder..... where that was left held 'open' for a period of lay-up, AND I suspect that the corresponding pistons rings arer likely to be 'gummed', and while these wont stop the bike running, they would account for the more promounced start on one pot phenomina... and at SOME point, running on a gummed ring... its going to knock out the bore and stop working on you.....

BUT we haven't got anywhere close to that yet....

After carb clean, we deal with tappets..... for which by better half has written a handy how to you can get a quick link to from my profile! And you can do the Cam Chaine tensioner at the same time.
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My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them!
Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?'

[lefty]

Cheers Mike.

Just hope that the weather is in my favour whilst I'm off work.

As soon as I'm done I'll report back.

[Steve.r]

Hi Lefty,

I was about to start a new thread then I saw this one. I have exactly the same issue on my CB125TDC. I also have a lazy left hand cylinder which is firing but not doing very much. Like you I have swapped all the electrics and fitted new spark plugs but nothing has made any difference. The engine will rev more smoothly with the left plug lead connected but disconnecting it does not make much difference at tick over. Disconnecting the right plug lead cuts the engine out immediately.

I have ordered one of those carb rebuild kits of ebay and am going to strip down, clean and rebuild both carbs when the kit arrives next week. I will let you know how I get on and will be watching this thread closely to see if you manage to resolve this one before me.

Steve.

[Teflon-Mike]

[Steve.r]

Hi Mike,

This is the kit I ordered

https://www.ebay.co.uk/itm/250990615471?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649

Do you think it looks correct? The stated jet sizes seem to be correct but beyond that who knows.

[Teflon-Mike]

[2011cagiva]

could it be to rich on one cylinder and to lean on they other? fuel to air mixture can alter how hot or cold an engine runs
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rb

[Steve.r]

[reckless_b]

when chasing faults like this I usually fit my colour tune "spark plug" its amazing what fualts you can see and fix when you know whats going on in the combustion chamber,
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40 years on the road on and sometimes off bikes with a very recent OFF