1981 Honda CB125T help needed

[Comuk]

Hi all,

Brand new member here. I have a 1981 Honda Cb125t-e, she has been serviced about 3 years ago and since then done less than 100 miles. I use her in private roads around my residence for fun and will keep it stock ie fully original as she is.

https://i.ibb.co/Scbj9Q7/E1-D77949-FE3-D-4320-934-C-2-C634-AD593-C2.jpg

Here is a video of me starting from cold

https://youtu.be/_7WJTosZieU

Issues I am facing and appreciate any advice on are:

- Starting: as you see in the video, it takes 4/5 attempts to start from cold. When I put in gear, it stops. I need to rev a bit and keep it there so that I can put in gear 1 and drive off

- rev counter: It slowly goes up and goes down. It is not accurate at all.

- Power: the main issue is the lack of power. She used to easily reach 50mph and pull strongly in 1/2/3 gears. Now on second gear, if it is a bit uphill, it cannot pull and slows down. Max it can do on straight line is 25mph. I noticed left exhaust has stronger fume push than right.

Where shall I start looking? I can ask a mobile mechanic to do a full service but I would love to work on it myself if it is easy enough. That is the whole point of owning her anyway.

Cheers
Mike

[Pete.]

The problem will be gummed up carbs most likely, though if it's unusually rattly that will probably be worn cams which they are prone for.

BTW you'll still get nicked riding it around your estate. Best stop doing that.
____________________
a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[Comuk]

[Pete.]

[Comuk]

Private road does NOT, you better check up on that. If the public have access then normal road traffic laws apply. Access has to be restricted to be otherwise.[/quote]

The roads get closed 1 day a year to make public access not possible and this makes it private. I am 100% sure and pay yearly ground charges as well.

Anyway, thats not the point of the thread. Thanks for your concern though

[Teflon-Mike]

Road Traffic Act aplies to ANY locationb that the 'public' have unhindered accessm which is somewhat uns2poecific, nd can be taken to include 'illegal' access, such as climbing a fence to trespass.. its down to interpretation.

That means Licence, tax, MOT & Insurance... which with the CB125T 'could' be problematic, it may be a 125 bgut strictlyt its NOT Learner-Legal or A1 complienmt.. LL/A1 regs opermit up to 125cc and Decimalised 14.5bhp at the crank 'declared' by manufacturer. Honda claimed 17bhp for the 125T so its actually outside licence limits unless modified, which could be awkward with insurance.

As to poor running... it probably needs a good thrashig.... these little motors dont much like being left deralict.. and I am pretty sure the early 125T's have points and condener ignition, and left unused points firr up and condensers dry out. It could need any number of bots of remedial, from a rtebore and rings, through carb clean and new gaskets to an ingitiion overhall.... get the Haybned book of lies and start with the normal service procedures, tppets cam-chain trension, fuel tank petcock, oil change etc etc etc.... and work your way down the list eliminating one possible at a time.
____________________
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?'

[Comuk]

Thank you T-M, you are quite famous for your posts for cb125t as google finds you in every search I did.

I have the said manual, let me start and post the progress to keep a reference to myself and maybe for others.

[Comuk]

I have purchased new ngk spark plugs. I went for cr8hs’s but when I removed the old ones, they were cr7hs. Are they compatible?

Then, I started removal of carbs. Even though manual said “raise the seat”, I tried to remove the seat with no success. One of the two bolts turns but doesnt move up or down, hence continued with raised seat. Removed the tank and surprised there is not a single bolt holding it.

Ok, now came the carbs, started with left hand side as suggested in the manual, I removed the fuel pipes from the fuel line and there is another pipe down but it is cut at one end. Then the throttle cables from both. So far so good. Then I am stuck. The manual says pull the clip backwards and then pull the carb out. I see there is a screw tightened ring on the front as well. I loosed that but the carb doesnt move an inch. Also the choke bridge is there, shall I not remove the link first?

I am afraid to damage it so left at there. Here is the pic of the carb sitting firmly.

Any advice is greatly appreciated

https://i.ibb.co/N1rbHXj/F62-AD74-F-54-B9-4-BEF-B9-F2-B488-C07-C096-E.jpg

[jaffa90]

I can see a carb or two sandwiched between the engine and the airbox with rubber tubed couplings, the engine side has metal straps crimped or jubilee clips, the air box side has coil sprung loaded holders.
I suggest that you consult a person with more knowledge about bikes.

[Comuk]

Thanks jaffa, there are 2 carbs linked loosely with a choke bridge, manual says you can take out one by one. The issue I see is that the plastic lost its elasticity. Either I will try to heat it a bit or try making some room by removing airbox.
Tried watching youtube, closest carb assembly are dirt bikes but there is no honda cb videos

[Comuk]

Ok, I managed to take the carbs out with a bit of heat and a lot of moving back and forth. Quite a lot of red gunk was built up. I cleaned and put back in. When I connect the throttle heads, the throttle sticks, the throttle snaps back if I dont screw in the heads so it is not the cable or throttle itself. Did I misassemble the carb? Is this an adjustment issue?

[Pete.]

Yes you probably have the slides in backwards. Look at the slide there should be a slot down one side and a wedge-shaped cutout at the bottom edge of the other. The slot locates on a pin to allow the slides full movement of travel but costrains rotation in the bore. The wedge stops against a screw with a tapered end which is the throttle stop/idle adjuster. If you get the slides in wrong the wedge cutout stops against the pin with the slide part way down.

BTW the red gunk is likely rust from inside the tank. Get yourself some inline fuel filters as there's going to be more where that came from.
____________________
a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[Fizzer Thou]

I also own a Honda CB125T2 which is a VERY long term project.For many years the engine sat on the side while I busied myself with other things like work,family and much bigger bikes.But occasionally I would spend some time on the CB.

When I did eventually get the engine running it did struggle to run off choke and after removing the carbs and the inlet manifolds I found that the 'O' rings that seal the surfaces had shrunk and split.Having resealed the joints with blue Hylomar the engine ran much better.These seals are shown on the fiche,part #16

https://www.cmsnl.com/honda-cb125t-england_model16528/partslist/E02.html#.XWMBxrg0rTR
____________________
Just talk bikes.What else is there?

Always have a 'Plan B'

[Comuk]

Ok - this was scary. I worked out the right way to put the throttle slides and the throttle is opening and closing normally. Well, in theory...when I started the engine, it didnt start for a few kicks, which I thought normal as all fuel was drained. Then, wrooom, it revved very high and I switched the engine off. Tried again, a loud bang. Now, I am scared to go near it
Looks like throttle is fully open but I can hear the throttle opening and closing. I can restart or just admit defeat and call a mechanic...what do you think? Anything to try before that, money is not an issue, I just want to do it myself

[Comuk]

[bikenut]

Oh, dear, I think we can all see where this is gunna end, a reasonably good looking old honda getting "£$% by an inexperienced kid. A cb125 at that which is ( was ) worth quite a bit now.

Get your self a manual, do you know of cmsnl for the exploded views??

Take the saddle off.

come back when the saddle is off.

if you cant get the saddle off, have you undone the bolts??

what bolts? i hear you ask

FIND THEM ON CMSNL!!!
____________________
nuts about bikes

[Comuk]

Hi bikenut, you made too many assumptions. I am 43 and own a very successful business, obviously not in motorcycle repair

How on earth you think I could get carbs out if I couldnt raise the seat (you dont need to remove it by the way) and take the tank off.

I have the original manual.

Now all issues are sorted, I exchanged the slides and all fine. Thanks for all the help!

[Comuk]

Saga continues. Bike starts up, idles at 1500rpm. Throttle responsive and it doesnt stall when I open the throttle. Looks like cleaning the carbs helped.

But one issue still remains, the exhaust on the left is not pumping air as strong as right one. Also, the exhaust pipe on right is very hot but left is mild. The idle screw responds instantly for right but does nothing for left. So I guess I am only on 1 cylinder and left one is not firing. I just changed the spark plugs and cleaned the carb so is it ignition the cause of this? This was an issue before I took out the carbs so I think the main reason why the bike was so slow was it was only pulling on 1 cylinder

[Grubscrew]

Looks likely.
Might be worth doing a compression test on each cylinder, at least it’ll give some indication on them.
____________________
FJR1300/CBR1000F

[Teflon-Mike]

[Comuk]

I have the haynes owners workshop manual printed in 1983.

It is suggesting just to raise seat. I realised it is much easier to get the airbox out first but the bloody seat wouldnt come up. One of the bolts is turning around itself and not getting unscrewed so I had to hear up the boots to get them out and in. They wont last another 1 or 2 diassembly for sure.

Yes my mistake, it is the throttle stop screw I am playing with.

[Comuk]

[Teflon-Mike]

You said it was 'serviced' 3 years ago... this means little to nowt, esp if coming from forfmer owner. Inference is its a deralict that has little known providence, and IF it were one of MY projerct bikes....
Top of the list a new lock set off e-bay woiuld be on tyhe list. They are about £50 and you get an ignition barel a seat lock and a steering lock. New lock-set means that all should work and one key fots all. Nest it means that you can cut to the chase and dril out the seat lock to lift the seat. From there you can get at the seat hinges. Unbolt and drop in a tub of old engine oil to soak. Hinge pin can then be pulled, and the hinge de-rusted for painting...
I would then puill the latch pin, and probaboy drop tht inb the same oil tube, to see if that would loosen up the catch, if not strip, de-rust, aned replace the spring.
Whilst the seat off, that air-vix could be pulled. Carb snorkled pulled from the inside; then the carbs could be pulled.
I would plop the rubber inlet manifolds into a tub in 1/4 inch of brake fluid, 'cos brake fluid has seal swellers in it, that will soak into the rubber and soften it.. Dont leave too long or they will go as boneless as a rubber chicken, but dip and wipe and leaved end in over-night.
Excavating deeper....
Motor would come out... cos that would let me hit the frame with a rotary wire for painting.. and deal with the mengine on the bench.
A top end rebuild would be on teh cards as course.... these little motors do NOT like being left deralict, rings rsust in the piston grooves, and go blunt and thise notors reving to 14K do NOT like blunt rings.
A Chinky barel kit costs aprox £100 and would be procured probably before I even got teh bike.. I think I have two on the shelf of 'ready spares' is our Snowie hasnt bicked one lol....
But a new barel kit is as cheapo or cheaper than a rebore and new pistons, and saves some running to and fro...
When ordered new gaskets would be ordered if not included in the kit.. but Valve stem seald would almost certainly NOT be in the kit and required.
If not already in the took-box, aldo on the order would be the Honda tappet key and lock-nut spanner, see How2 posts in profikle for part numbers. Also the tappets.. they are probably peened to heck at the vaklve end if former owners didn;t do the clerances every 1ooo miles, the adjuster drive aquare probabloy chewed like a dogs dinner is they did, but didn';t have the Honda tappet key..... new tappsts are about £3 and dave Soooo many silly Q's later.
Head off, cam would be evaluated.... cams dont fare well if oil changes neglectyed and or bike had ever run on its side and or been thrashed.
A Genuine T or T2 'should' have the roc king horse poop, 309 spec 'full power' cam... good liuck if its still there, but you have paid your money and taken your chances.... even a chewed up one is likely better thanb the cheapo chinky spec cams based on the last off TD-J profile, detunbed beneath even the TD-C/E spec cam. But even a good Super-Dream cam shoule have enough get up and go in it, and isn't so prone to fail and is more tolerent of wide tappets.
The e-bat cams though do tend to come with new cam bearfings and they can be worth the mone for them alone, and new cam-caps will take out a lot of slop from a worn cam.
A new cam-chain would be a good shoyt, but begs a bottom end tear down to fit. Hint here is that IF the cam goes back in reletively easy, then the cam-chain probably stretched and bottom end tear and a new cam-chain needed... if not live with it.
Grind in the valves to get a good seal on them, before fitting up new barel.
Fit up new barel and pistons with new gaskets and Pay close attension to both the proppr toirque specs and order.. warning thery are LOW torque fasteners.. you will probabloy need a low-range torque wrenbche and 1/4" drive sockets... not too expensive if you have to buy new else get a borrow... you only need once or twice!
Complete top end and if points pay attension to free off and lube the advance mechanism, and fit new points AND condenser.
Job jobbed, motor ready to go back in.. before that pay as much heed as you need to the cyckle parts.
I would replace the steering head-race bearings as a matterf of course, and probably with a taper bearing set.
Swing arm would come off, be de-rusted and checked around the brasing; of good new bushed would be pressed in, then it would be fitted back up to painted or coated frame, depending, with the back-brake overhauked and probably new chain adjusters as they tend to get chewed.
New shocks would probabloy be on the cards too.
Leaves the front brake...... which would be a niggle.
Front beake is a rather wampy mechanical disc that I absolutely HATE. Cause of sonsternation and main issue of project philosophy. IF philosophy is to maintain originalityy then the only option is to use it, and overhual as best as by the book... and photo-copy the pages its routine maintenence on these, IF you like to stop when you want it to!!! It wil need stripping and cleaning and greasing regularly, an I would treat it to a brand new cable ASAP and pre-soak new vable in oil before fit.
If originality NOT so importanty, I would swap out that bront valiper for a hydraulic arrasngement. ISTTR that the single pot caliper from a 250N is a direct fit, but che3ck micro-fishe! Othersise one of the CG grippers should work.. if seconf hand parts procured for conversion, they woulr be overhauled with new piston and seals and hose before fit.
Fortks would be pulled and stripped and new seals and oil added.
EVENTUALLY ~ might get back to that seat and ponderation of whether iot needed a new cover and the bade de-susting and restoring...

IE.. whether the engine rin let alone ran even close to 'well' would be right at the bottom of the list after the thick end of a grands worth of work.... you have been warned....

These were not cheap bikes when new, it was the main grip against them, nor werer they low mintenence, anotyher gripe, consequentoly few got the care and ttension or money they needed chucked at them, and tended to fare worse than most 125's for low rent mechanics, yet nbe bikes most afflicted byu them... with luck this is a later Other market importy that WAS possibly a bit better looked after and brought onto this country in the last 30 years to be neglected!!!

If you 'think' you can scrub one of these up in a long weekl-end for a few pence yopu are likely to be sorfe dissapointed... and the morte shorty cute you take in originbal resussitation so the more likely you are to puish prfetty majhor maledies into early sevice... particulrly knackered bores/rings hence advice over the top end rebuild.

IF they are done, and done well though, well, they are still a 40 year old 125 that will never set the world alight.... might surprise a few contemprary boy racers on CBR's or YZF-R125's though and thrashing them well past the 12K blood-line is not just 'fun' but nie on mandatory.... and they actuaklly NEED it to get the oil flowing and the plugs clean.... but the price IS that they are a high maintenence motorcycle.... and fo demand frequent oil changes and tappet tickles and the CCT is both manual and finikity.... They remain still the most powerful 'standarfd four-stroke 125 ever sold..... but they are also still almost 1/2 centry old c lunker classics, and beg care and attension and a little more considered use....Just dont espect it on the cheap.. that they dont do... and never have.

PS a new barel kit will make a compression test redcundant, and on such small cylinder a compression test is pobably prett useless anyway.
____________________
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?'

[Comuk]

Thank you Tef. All these needs to be done, I will keep the bile stock and will do a full restoration. However, one cylinder not firing is the top of the list now. Once I get that done, I will not go for fine tuning until all other things are sorted.
Your list in no way discourages me, actually quite the opposite. If I am done with it by Easter, I would consider it a success.

[Teflon-Mike]

Motor is only half the word motorbike; the engine is the LAST thing you need make work, NOT the first let alone only....
Old rule of resto; BEORE you try make it 'go' make sure you can make it STOP, and preferably go in the direction you want.....
The mechanical caliper on the front of these is something I would prioritise above probably most else... if theyt work they tend to ladk feel and be grabby; and that's if you are lucky and it even remotely works.
They are prone to gum up.
Rear shocksw are non adjuctable and non rebuildable; they started life with little or no damping and got worse from there. Front pogo sticks similarly; engine had oil and book says it should be changed everu 1oo miles, but pogo sticks are full of oil too,. and that seldom EVA changed; so front braked and a fork overhaul would be top of my list of prioritises IF I actually wanted to ride the thing, not park it on a pedestal as an obje d'art....
So....
Advice is stop faffing with carbs and motor and worry about the important stuff FIRST... and cut to the chase and do a propper engine rebuild.... odds is you will have to sooner rather than later anyway, and though a ball-ache actually one of the least oberouse jobs top be done.
____________________
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?'