Honda CB125TDE RUNNING PROBLEM

[haydo720]

Hi Guys and Gals.
I still cant get my Honda 125tde superdream to run right. when I first got the bike it had standard twin carbs on it and the inlet manifolds where all shot and cracked. My symptoms are, the bike starts and idles like a dream but when you rev her up she picks up very slowly. She does rev right up but no where near as quickly as it should. I originally put this down to air being sucked in somewhere i.e the split manifolds. But I have recently purchased a CM125 2 into 1 manifold with the carburettor as well. Started her up and she still runs the same. so I am just looking on advice as to where to look next? Could it be possible that it has a stuck valve?

[grahamxs500]

Last bike i had with that problem was a blocked airfilter
Revved normal in neutral but wouldn't pull in gears /had the airfilter box
Covered blocking the opening where it pulls air in

[Teflon-Mike]

Compression Test?

Otherwise, I've always found a lot of supposed 'carburation' issues are actually in the exhaust, not the carb. Any blowing at the flange? What do the studs look like, are they thin around the flange clamp? Is it still running OE twin-pipes, or has it got a 2 into 1 on t? OE Twins rot in the balencer pipe; Motad 2-1's seem to always get kerb-clobbered on the lower header bend, where they are want to pin-hole; Micron's seem prone to rot through at the rear hanger....

Likelihood is, that the motor is 'tired'. I have got to the point that when look at one, and think "OK, lets fire it up and see what we got..." The next idea in my head is "OR.. shall I save myself the hassle and just pull the motor and do a top-end?"... I am not a pessimist! I am a disillusioned optimist, disappointed too often.... so I'll give it a tickle, but I keep e-bay barrel kits, on the 'spares' shelf!

Top end is close on a ctrl+alt+del 'reset' for one; job sees the valves lapped; stem seals swapped; head gasket replaced, and the cam-re-timed, CCT ungumed and properly set; all eliminating a lot more variables than just bore & ring wear, parts replaced suggest.

£100 for a kit of e-bay; I can comfortably do one in a day, these days, including pulling the motor out the frame and putting it back in; clamp up the exhaust 'loose'; fit carbs, fit air-boxes; pay attention to the choke link; pilot air screw, all the way 'in' then five 1/4 turns back 'out'... AND if it wont start, swap the coil connections... and 3 times out of five, all I need to do after that, is nip up the exhaust flange.

It can be a lot less hassle than chasing around the outside of the motor, in the 'hope' you wont have to look inside...

I'll leave you to ponder the notion, 'cos its likely where you'll end up sooner or later.
____________________
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?'

[haydo720]

Hi @Teflon-Mike,
Thanks for the reply. I went to do a compression last night and to my horror, I found that whoever had the bike before me had pulled the threads on the spark plug holes and tried to cobble up with extra gasket washers

So head off is a must anyway to get these repaired (£35 a hole from my local machine shop. And the extra cost for the barrel, pistons, seals and time is leading me away from a rebuild and might just sell this as a non runner (cosmetics aren't brilliant either).

I've never been inside one of these bikes and riding 2 stroke mx bikes, I am not overly confident inside 4ts anyway.

Are these bikes worth the hassle and money to get going ?

[Teflon-Mike]

You shouldn't 'have' to take the head off to get the plug-holes heli-coiled.. might make it easier to make sure the lock-tang is properly seated, which is where a lot of problems with coiling occur; but can be done with the head on, and even engine in the frame.

£35 a coil is a bit steep though... Head, is common across the Benley family; CB/CD/CM 125, 185, 200 & 234.. you ought be able to source a second hand head, complete for the price of one coil.

OR, new chinky head castings are on e-bay for about £70... new spark-plug threads, new valve guides, new seats.. job-jobbed with bonus. Barrel kits are about £100, with gaskets.

Go 'New' head casting & Barrel kit and for £200 and some spanner faffing; you have an almost fully reconditioned engine.

As to how tricky it is? Like I said, get the bits, and I can lift the engine out, strip the top end, re-build with new bits, and have the engine back in the frame in a day.... 'chore' job that takes time, is lapping in the little valves in the head; but with a new casting not really an issue, just a light lap to clean up the valves and match to the new seats and they should be good.

Pressed up crank in the bottom end, fitting the pistons & barrel is just like on a two-stroke; and it don't have any power-valves in it to worry-about or faff with... they are n the head, and all you need worry about there is aligning the timing marks, and looping the cam-chain.. little bit of attention to detail & care and it shouldn't be any more difficult, onerouse or scary than any other old motor. There are certainly many two-strokes I would be more nervous of tearing into.. usually with 'KHI stampings on them.. but all swings and round-abouts.

Are they worth it? - Err.... well all rather depends what you hope to get for it....

I you haven't dug into a four-stroke before, then, just the experience of pulling one to bits could be enough to make it worth while.

Here and now, at forty-four years old, with a full licence for over half of them, I find them quite charming.... It's obvious that it was a bike designed by focus group, back in 1980, and Honda tried to deliver 'everything' the marketing men said that customers wanted.... and remarkably achieved an awful lot of it.. but as they say, the camel was a horse designed by committee... it was a sales flop, 'cos while it's a pretty good all-round package, it lacked any great strength to get buyers blood up... apart from a price tag that was far too steep.

Properly set up and in decent nick, they are a genuine 70mph 125. The motor, can be a peach; its no where near as 'lumpy' as the 4T singles, so it will trickle nicely at slow speeds without the snatchiness singles show, and it'll rev out, pulling to 14K where the singles start to wheeze much over 9K. It'll pull solidly low down, and you can use the higher gears quite happily between 3&6K before it 'comes on the cam' and gets a bit more eager.. doesn't come in with such a 'power-band' rush as a 2T, but it has a little of that picking up its skirts and hustling nature.

Handling? its old-school. 'long & low', rather than'over the nose'. Back ends need fettling; sloppy or seized bushes or a saggy shock will ruin one; forks need decent oil in them, and perhaps a tad of extra pre-load to firm them up a bit. But, set up, and shod with decent tyres, I can deck the pegs with abandon on one.

Carrying their weight lower down, and over a longer wheel base, they are a lot less 'flighty' than typical commuter singles, and less ruffled by side-winds or surface changes and stuff. It's a re-assuring ride, and get used to that, you can start taking a lot of liberties with it.

Meanwhile; they are pretty comfy; the riding position is very useful; its not scrunched up, yet still gives good viability and easy control; while the thing will return decent mpg.

As an all-round package, that committee did manage to pack an awful lot into one little bike; its a very useful round town commuter; it can be quite good fun on the back-lanes; it can hack it on the by-pass, and its comfy enough to even go touring on. It's not even that bad 2-up, and you can chuck a fair bit of luggage on one.

At 17 years old ALL that was utterly lost on me! It wasn't a two-stroke... so as most of the market, I was suspicious about 'reliability' and concerned that if it broke, it would be a pain to try fix; while it was going to be 'slow' to start with, and not have the easy option of wapping on a spannie to make it less so. so I bought a Kawasaki AR125.. which I have no regrets over.. but I never fitted a spannie, or had to mess with its reed-and disc induction!

In the modern world, an AR would be a nice little nostalgia toy; I have looked at a couple and had project ideas.. b-u-t... rose tinted spex will only get you so far! Reality would be a very much bigger challenge to try tacking one of them; I tackled an air-cooled DT instead, which was 'fun', but expensive, and not a very practical bike at the end of it.

Super-Dream, in that respect is a lot more 'do-able'. Costs never add up at the end of the day; knackered old examples to start a project on aren't so ambitiously priced... and are more common, but then, even 'mint' original examples or fully restored ones, don't command particular interest or great resale prices. Economically they aren't a very good bet to chuck money at... if any bikes ever are.... BUT... that all-round usefulness they have? IF you can get the value out of one from using it.. and THEN they can start to be worth it.

Fettled, and made reliable, and with the maintenance to keep them in fettle.. you have an every-day "Classic" that can earn its keep, not just as a bit of sunny-day evening fun, but all weather commuting, and more adventurous week-end excursions.

It CAN be worth it..... but as an every-day ride, a more sensible person would probably be better off buying a YBR... no guarantee, of course that that wouldn't give grief, or cost as much the long run. B-U-T... if we were sensible why would we buy a bike in the first place?

The Thrill, of getting on a bike, you have turned from a derelict heap of scrap, and brought back to life, and can ride anywhere, no matter what the bike, is awesome.. that alone can be 'worth it'.

But 125 S-D? Even stood there, listening to folk, deride it; and they remark on how much time or money you have 'wasted', and tell you you could have bought a 'better' bike for the money; it washes off, 'cos ANY-ONE can open their wallet or sign their soul to the shylocks to just BUY a bike.. When they tell you you could have done something bigger, more interesting or more exiting..... again.. it washes over, because yes.. you could.. but could you have made 'use' of it at the end? How much 'fun' is a bigger bike taking up more space in the back of the shed gathering dust? How 'interesting' is it when only you see it, when you stub your toe on the centre stand trying to reach over it for a can of paint? and how 'exiting' is it, if its only outing is two miles to the MOT station and back?

End of the day... dictionary definition of a project, is any endeavour YOU choose to undertake... so only YOU can decide if it's worth it.

125 Super-Dreams? They are an under-dog and always have been. That alone, might make one worth it; but otherwise, they do have a fair bit that can make them worth the doing; certainly as much as any other old 125, and more than many.

BUT, it's your call, and your call alone.....

Do you want a 'project'? Or do you want a way to work? How much do you want 'toy' and how much do you need 'transport'

And hint, vis your concern its cosmetics is a bit tatty; last thing on the list; far too many spend all their attention on paint and pretty, and end up with a pile of pretty painted scrap they call a resto. Get the mechanics sorted and you have a bike that'll do the job... you dont need side-panels or tail cowling to get it through an MOT let alone use the thing.... and you can deal with them any time you like, as nicely as you like... only bit of body-work I'd tackle before, would be the INSIDE of the tank; clean, flush, electro-de-rust, casustic clean and pickle for a POR-15 treatment, so stave 'carburation' problems from chitty fuel, before they start.
____________________
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?'

[pits]

This should help

A VERY Basic Bit of 'Technique' to hep avoid stripping cylinder head threads!


THAT'S SO SIMPLE!" you say. "WHY do you need a Photo-How to for unscrewing a spark plug?!?!" That's what I thought; & even Tef, who will never give the 'short' version if a 10,000 word essay will suffice, didn't think it was THAT worth mentioning.... BUT, after answering the FAQ "Stripped Spark Plug Hole, What's a Helicoil' umpety hundred times...... he thought it MIGHT actually warrant a mention! Prevention is better than a cure, after all! So!
EXCESSIVE FORCE IS NOT REQUIRED

& Socket Sets are your ENEMY! Far to easy to apply far too much force. But, often only tool in the box that will fit a motorbike spark-plug, and buried deep in a casting with double overhead camshafts either side it can sometimes be awkward and the extensions & knuckle joints, can be useful, but be warned, more between your finger tips and spark plug, less 'feel' you have to avoid over tightening or cross threading.

https://i178.photobucket.com/albums/w269/teflons-torque/Little%20Dreams/Tappets/imag2532.jpg


Keep the socket as square to the spark plug as possible. Let the socket 'fall' over the plug, grip the ratchet 'loosely', and apply a gentle even pressure to the end to start it turning, and hold the centre of the socket over the centre of the spark-plug.
https://i178.photobucket.com/albums/w269/teflons-torque/Little%20Dreams/Tappets/imag2533.jpg



As soon as the initial pressure is taken off the plug, STOP using the leverage of the ratchet. Remove it and if you have to use the socket or extension, twist it like a screwdriver, with 'finger force' only, until you feel the plug starting to 'wobble' in its threads.
https://i178.photobucket.com/albums/w269/teflons-torque/Little%20Dreams/Tappets/imag2535.jpg


THEN wind the last way out, wherever possible PURELY with your fingers.
https://i178.photobucket.com/albums/w269/teflons-torque/Little%20Dreams/Tappets/imag2571.jpg
Refitting plugs is pretty much the reverse.



Putting the plug in; START the plug VERY gently. Avoid just 'dropping' the plug down the spark plug rebate. You do NOT want the electrode on the bottom holding the critical 'electrode gap' to get bashed on the cylinder head and closed up. Engine wont run well if it does. So try and lower it in, preferably with your fingers, and get it central in the hole, before you get metal touching metal.
https://i178.photobucket.com/albums/w269/teflons-torque/Little%20Dreams/Tappets/imag2572.jpg


THEN, again, with your fingers, GENTLY get the spark plug square and twisting into the threads, without cross threading. This high up the hole the plug can 'wobble' a bit, so don't force it, tickle it into the threads.
https://i178.photobucket.com/albums/w269/teflons-torque/Little%20Dreams/Tappets/imag2574.jpg



As removal, if you need to use socket and or extension like a screw driver to wind the plug to the bottom of the hole. ONLY when it has bottomed out, do you need to use the ratchet, and THEN only with finger force to just 'nip' the sealing ring between the plug and head.

Again, cradling the ratchet to keep it central over the plug, and using 'just' finger tip pressure on the handle to apply that 'nip'.
https://i178.photobucket.com/albums/w269/teflons-torque/Little%20Dreams/Tappets/download.png


This handy guide was offered on the matter of what that 'nip' may be! Discussion was also had on the topic of using a Torque Wrench, but if you know how to use a torque wrench, you probably don't need this How2!

The Tightening torque on a Spark plug is VERY small; maybe 8ft-lb/10nm/1.1kgm, and most Torque Wrenches, sold to do up cylinder head bolts and things, don't go down to torque settings that low. So the Danger is if you were told to use one, you would very possibly pick up a 'High Range' torque wrench, and confused by the scale, pick a number that is 'similar' to the specified setting, but could be 10, 15, 100 or even 150 times what's needed, and actually be MORE likely to strip your cylinder head threads than NOT using a Torque Wrench!

So be careful of your spark-plugs and gentle in their handling, and your cylinder head will thank you by NOT stripping its thread.

If you are clumsy, brutal or lazy, with them? Well, then the likelihood is you will suffer a cross or stripped thread.

If you do, and you are lucky, the thread may merely be cross threaded, and a 'cleaner die' might be used to reform the damaged threads.

If not, then it will probably require helicoiling; which is a process of drilling out the damaged thread, and cutting a new larger one, the same pitch, and winding in a coil of metal wire to sleeve the thread back to the spark plug size.

If you are very lucky, then this might not need the engine removed from the bike, or necessarily the engine stripping so that the cylinder head can be drilled. But don't bank on it!

And once helicoiled; make the same mistake again, and you can strip the insert AND thread in the cylinder head, and do THAT, and chances are there is probably no cheap or easy fix!

So, prevention is better than the cure, and ALL it takes is a little care and attention.
____________________
Stinkwheel: You have no right to free speech
00:32:08 Blau Zedong: yes, i am a massive CB400 fan and collector
00:33:00 Blau Zedong: the CB400 is my favourite road bike