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Deleted1212 |
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Deleted1212 L Plate Warrior
Joined: 18 Nov 2019 Karma :
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Posted: 11:31 - 18 Nov 2019 Post subject: 1981 Honda CB125TB |
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Hi All,
Here is my honda cb125tb with a t2 engine. i have just finished rebuilding the engine and carbs, but cannot get it running well. It is running too rich, and i am also not really used to these carbs being primarily a car person! (I have a pair of old BL triumphs that have a single SU, so piss easy to tune)
https://live.staticflickr.com/65535/49084037162_3b96b10c0f_c.jpg
I am learning to ride but so far haven't had much seat time, before the rebuild it was smoking like a 2 stroke from one cylinder so did stem seals and rings and it has mostly sorted it. It still smokes but it's fuel rather than oil. I have played around with the float height to try and get it to ~18mm from the bottom of the float, but it is still running rich and not doing the plugs any good. Any tips on tuning these bikes? Just want to be able to ride the damn thing! Cheers.
More pics of the rebuild to follow ____________________ 1981 Honda CB125TB (With a T2 engine) |
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Deleted1212 |
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Deleted1212 L Plate Warrior
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Easy-X |
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Easy-X Super Spammer
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Posted: 12:08 - 18 Nov 2019 Post subject: |
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Am I reading this right:
https://www.howmanyleft.co.uk/vehicle/honda_cb125tb
Apparently you have the only one on the road The DVLA database is a bit wonky for anything before SORN was introduced but probably you have one of the few left on the road
Let's assume the carbs are working for the moment. If it's running too rich then either it's not getting enough air or there's some exhaust restriction. Test it with the airbox off and check the exhausts for blockages.
After that are both cylinders firing - both downpipes getting hot - or just one? ____________________ Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter |
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Deleted1212 |
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Deleted1212 L Plate Warrior
Joined: 18 Nov 2019 Karma :
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Posted: 12:35 - 18 Nov 2019 Post subject: |
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Easy-X wrote: | Am I reading this right:
https://www.howmanyleft.co.uk/vehicle/honda_cb125tb
Apparently you have the only one on the road The DVLA database is a bit wonky for anything before SORN was introduced but probably you have one of the few left on the road
Let's assume the carbs are working for the moment. If it's running too rich then either it's not getting enough air or there's some exhaust restriction. Test it with the airbox off and check the exhausts for blockages.
After that are both cylinders firing - both downpipes getting hot - or just one? |
I wouldn't be too surprised if it was the only one! I think i still have the TB engine if i wanted to restore it to completely factory but i'd rather have the t2 engine and goodies like rev counter etc.
will test with airbox off later, haven't tried that yet with the new engine in. Both downpipes get hot, but it seems like when it warms up it starts firing on one cylinder. I wonder if the coils are no good or something and don;t like heat? they are right above the cam cover so would surely warm up a little bit. ____________________ 1981 Honda CB125TB (With a T2 engine) |
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Easy-X |
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Easy-X Super Spammer
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Posted: 12:47 - 18 Nov 2019 Post subject: |
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Oh yes, the engine swap. How much did you swap over? Fuel system, carbs, electrics, etc.
For example: if you swapped all you could you might end up reusing the original airbox and exhaust system which, unless identical between models, would probably mean rejetting the carbs.
<addendum> well they do look identical to my untrained eye but unless the part numbers [of the airbox/exhaust] match there may be differences you need to account for. ____________________ Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter |
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Deleted1212 |
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Deleted1212 L Plate Warrior
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Teflon-Mike |
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Teflon-Mike tl;dr
Joined: 01 Jun 2010 Karma :
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Posted: 15:47 - 18 Nov 2019 Post subject: Re: 1981 Honda CB125TB |
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rerpha wrote: | I am learning to ride | You do Know that this isn't UK Learner-Legal A1 complient don't you? It may be a 125, but when they changed the laws to up the Learner-Legal power limit to the EU harmonised 15bhp (Manufacturers claim) the CB125T was already outside of the limit, at 17bhp? Wow! To all practical purposes it makes no odds, especially as your example isn't making any bhp at the moment, b-u-t, it may if/when some-one comes to check the paperwork, and it dont match up.... you have been warned!
Elcewise... this is a forty year old motorcycle, that has probably spent a large chunk of its life laid up derelict.... they don't like that much... anything and everything is likely worn out and or gummed up by now.
Personally on all my 126 twin projects my FIRST recourse these days is to do a full and propper Top End Rebuild, on the thing... see handy how2's in profile. These little motors do NOT like worn bores or less than eager piston rings, whilst the valve stem seals have a tendancy to turn to talcum-powder. A Top end rebuild nails just 'soooo many; possible problems at source, and cuts to the chase as far as later fault finding, cos you KNOW that the top end should be good.
I would NOT be muggeing about with the carbs at this stage. Motor is only half the word Motorbike, and even less of one.
Before you 'Go' make sure you can 'stop'.. and preferably go in the right direction.
These have a 'horrible' cable operated disc brake on the front, that was never particularly wonderful even when new, and will NOT have gotten better with age!
That would probably be my first candidate/tack on this thing, and for originality, it would have tgo be properly overhauled, and set up. For the fess, I would probably be thinking about front end upgrades, and either the entire fork-assembly off a TD... 'cos that got a disc brake, and I have more than a couple lying about. though would beg the TD comstar wheel to match, cos the discs have different offsets... Or I'd be pondering bits from later disc braked CG 'cos I 'think' they have the same diameter fork stanchions....
B-u-t the CB100N shared the same cable operated disc brake, and I have NO fond memories of that what-so-ever. It was at best 'wooden' lacking feel, at worst, it just didn't slow the wheel, but worse than worse, it could do any or either any time it liked, and using the front brake lever was like playing Russian Roulette, especially in Brummie Rush-Hour"
Anyway; that niggle targetted, forks rebuilt, I'd turn attension to the back end, where the rear 'suspension' units would almost certainly find thier way into the scrap heat in a nice parabolic trajectory. They lacked damping at the best of times, odds they have any now is near nill.. is they do it'l be rust and crud impinging damper rod progress, I suspect. They would be swapped out. Whilst down there the swing arm bushes would come in for replacement,m and good chance to see how much metal is left in the swing arm.
THEN, onto such luxuries as... mudguards and body-work, and the little niggle of the 'electrics' which are never much fun, but hampered on this particular route to the asylum by being 6v.... a 12v conversion with Benly bits and possibly even an e-start, would be strongly considered.
BUT when I had sorted or sorted a plan for the cycle parts, like that front brake, I MIGHT get around to doing something with the engine, which as said would start with chinky barel kit and a top end rebuild....
THEN carburettors may be a bit of an imperative.... and a bit liker the engine, I would plan a complete overhaul.. after sourcing some nice new hole free exhausts.
I would be wary of the e-bay carbkits... in fact I had an argument with WeMoto over some they listed for the 125Twin, that were actually Chinky bits for the CG, and contained not only the wrong float needles, but wrong size jets.... you have been warned... a-g-a-i-n. DSS I believe ran out of 'official' carb spares for these about a decade ago, so its down to getting a generic CG kit to salvage what bits you can from it, like the float bowl seals and the idle-air screw.... on which note almost certainly worth a look, they have a very fin needle on the eld, wont to corrode into the carb-body... and snap.... oft replaced in ignorance by folk that then say that it makes no difference, more often with two or no rubber O-Rings! More warn!!
B-u-t long and the short of it is that basically on the list of things to worry about.... setting the float height IS a long long way down... and even a well fettled carb will pee fuel from the over flow, cos the needles stick in their guides....
Advice is start from the top, and work methosically down the list, slowly and carefully, with LOTS of known an trusted new bits.. dont 'buy' problems you dont need.
Best of British, with it, anyway.
Add on ED: you say PO did the engine swap.... can you be sure its a T2 motor? Almost all the Benly twins are interchangeable in the frame mounts. The Benly and CM motors oft also have the round rocker covers tat 'look' T" ish, but even they are a quick swap. B-U-T the T's have a 180 timed crank, the CDs & most CM's a 360 timed cran. When you pulled the top off to look at valve stem seals... were both pistons at TDC/BDC together? Can you be sure it's a 180 timed T motor? If not, it would run like a bag off, on only one pot, if it's trying to spark the pots at the wrong time. Whichh dont help much with the carbs... but as said, they would not be very high up the priority list.
On The Topic, worth mentioning the carb-rubbers, which have a tendency to perish, and on this should be flanged for the 26mm carbs, but also tend to get torn with folk ripping the carbs out brutally. Also rather unobtanium... so good luck there and be careful with what you got, if messin in that region. Lots of botches with sily sealant, insulation tape and super-glue are known! ____________________ 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?' |
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Robby |
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Robby Dirty Old Man
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Deleted1212 |
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Deleted1212 L Plate Warrior
Joined: 18 Nov 2019 Karma :
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Posted: 23:03 - 19 Nov 2019 Post subject: Re: 1981 Honda CB125TB |
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Teflon-Mike wrote: | rerpha wrote: | I am learning to ride | You do Know that this isn't UK Learner-Legal A1 complient don't you? It may be a 125, but when they changed the laws to up the Learner-Legal power limit to the EU harmonised 15bhp (Manufacturers claim) the CB125T was already outside of the limit, at 17bhp? Wow! To all practical purposes it makes no odds, especially as your example isn't making any bhp at the moment, b-u-t, it may if/when some-one comes to check the paperwork, and it dont match up.... you have been warned!
Elcewise... this is a forty year old motorcycle, that has probably spent a large chunk of its life laid up derelict.... they don't like that much... anything and everything is likely worn out and or gummed up by now.
Personally on all my 126 twin projects my FIRST recourse these days is to do a full and propper Top End Rebuild, on the thing... see handy how2's in profile. These little motors do NOT like worn bores or less than eager piston rings, whilst the valve stem seals have a tendancy to turn to talcum-powder. A Top end rebuild nails just 'soooo many; possible problems at source, and cuts to the chase as far as later fault finding, cos you KNOW that the top end should be good.
I would NOT be muggeing about with the carbs at this stage. Motor is only half the word Motorbike, and even less of one.
Before you 'Go' make sure you can 'stop'.. and preferably go in the right direction.
These have a 'horrible' cable operated disc brake on the front, that was never particularly wonderful even when new, and will NOT have gotten better with age!
That would probably be my first candidate/tack on this thing, and for originality, it would have tgo be properly overhauled, and set up. For the fess, I would probably be thinking about front end upgrades, and either the entire fork-assembly off a TD... 'cos that got a disc brake, and I have more than a couple lying about. though would beg the TD comstar wheel to match, cos the discs have different offsets... Or I'd be pondering bits from later disc braked CG 'cos I 'think' they have the same diameter fork stanchions....
B-u-t the CB100N shared the same cable operated disc brake, and I have NO fond memories of that what-so-ever. It was at best 'wooden' lacking feel, at worst, it just didn't slow the wheel, but worse than worse, it could do any or either any time it liked, and using the front brake lever was like playing Russian Roulette, especially in Brummie Rush-Hour"
Anyway; that niggle targetted, forks rebuilt, I'd turn attension to the back end, where the rear 'suspension' units would almost certainly find thier way into the scrap heat in a nice parabolic trajectory. They lacked damping at the best of times, odds they have any now is near nill.. is they do it'l be rust and crud impinging damper rod progress, I suspect. They would be swapped out. Whilst down there the swing arm bushes would come in for replacement,m and good chance to see how much metal is left in the swing arm.
THEN, onto such luxuries as... mudguards and body-work, and the little niggle of the 'electrics' which are never much fun, but hampered on this particular route to the asylum by being 6v.... a 12v conversion with Benly bits and possibly even an e-start, would be strongly considered.
BUT when I had sorted or sorted a plan for the cycle parts, like that front brake, I MIGHT get around to doing something with the engine, which as said would start with chinky barel kit and a top end rebuild....
THEN carburettors may be a bit of an imperative.... and a bit liker the engine, I would plan a complete overhaul.. after sourcing some nice new hole free exhausts.
I would be wary of the e-bay carbkits... in fact I had an argument with WeMoto over some they listed for the 125Twin, that were actually Chinky bits for the CG, and contained not only the wrong float needles, but wrong size jets.... you have been warned... a-g-a-i-n. DSS I believe ran out of 'official' carb spares for these about a decade ago, so its down to getting a generic CG kit to salvage what bits you can from it, like the float bowl seals and the idle-air screw.... on which note almost certainly worth a look, they have a very fin needle on the eld, wont to corrode into the carb-body... and snap.... oft replaced in ignorance by folk that then say that it makes no difference, more often with two or no rubber O-Rings! More warn!!
B-u-t long and the short of it is that basically on the list of things to worry about.... setting the float height IS a long long way down... and even a well fettled carb will pee fuel from the over flow, cos the needles stick in their guides....
Advice is start from the top, and work methosically down the list, slowly and carefully, with LOTS of known an trusted new bits.. dont 'buy' problems you dont need.
Best of British, with it, anyway.
Add on ED: you say PO did the engine swap.... can you be sure its a T2 motor? Almost all the Benly twins are interchangeable in the frame mounts. The Benly and CM motors oft also have the round rocker covers tat 'look' T" ish, but even they are a quick swap. B-U-T the T's have a 180 timed crank, the CDs & most CM's a 360 timed cran. When you pulled the top off to look at valve stem seals... were both pistons at TDC/BDC together? Can you be sure it's a 180 timed T motor? If not, it would run like a bag off, on only one pot, if it's trying to spark the pots at the wrong time. Whichh dont help much with the carbs... but as said, they would not be very high up the priority list.
On The Topic, worth mentioning the carb-rubbers, which have a tendency to perish, and on this should be flanged for the 26mm carbs, but also tend to get torn with folk ripping the carbs out brutally. Also rather unobtanium... so good luck there and be careful with what you got, if messin in that region. Lots of botches with sily sealant, insulation tape and super-glue are known! |
Ok, so here is the new stuff i have replaced:
- New chinese spec pistons and rings
- New chinese barrel on there which i honed when doing so
- New valve stem seals
- Keyster carb rebuild kit - is this what you meant by ebay carb kits? it said t2 on the box but not entirely sure if it's right or not.
- brake rotor arm - tried a few but the bearing races were very worn and were causing the brake to bind - i know what you mean about them being a bit shite. It is at least now all working properly as we found a NOS rotor arm and replaced it and the cable
I am almost certain it is a t2 engine, the previous owner said he checked the engine number and it was indeed a t2 motor. I think it is timed 180 degrees as there are two marks on the alternator stator/flywheel each side - that being said i think a spare TD engine i have may have the same on its 12v alternator stator, does that sound correct?
Previous owner had replaced most of the rear end from the looks of it, new shocks and springs and the swingarm looks to be in good nick.
The carb rubbers WERE split, but i have replaced them for good ones. O rings and washers were replaced when i did the rebuild and made sure to remove old o-rings.
I just want to run the engine in properly, but if i can't get fueling working properly i'm not sure what to do. I have turned the pilot mixture jets out 1 1/4 turns like the haynes manual says, but im not sure what would be ideal really as im guessing it is basing that off of old leaded/4/5 star fuel?
Either way it is fouling both plugs, not wet just black, so convinced its the carbs. ____________________ 1981 Honda CB125TB (With a T2 engine) |
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Deleted1212 L Plate Warrior
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Easy-X Super Spammer
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Shaft |
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Shaft World Chat Champion
Joined: 27 Dec 2010 Karma :
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Posted: 00:26 - 21 Nov 2019 Post subject: |
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You could always make up a manifold and fit a DCOE, at least you won't have balance issues
More seriously, I'm not a fan of pattern carb rebuild kits, I've used a few and they always seem to be inferior to OE kits in some way.
Have a look and see if David Silver do a genuine part. ____________________ Things get better with age; I'm close to being magnificent........
20 RE Interceptor, 83 Z1100A3, 83 GS650 Katana
WooHoo, I'm a Man Point Millionaire! https://www.bikechatforums.com/viewtopic.php?t=234035 |
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pepperami |
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pepperami Super Spammer
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Deleted1212 |
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Deleted1212 L Plate Warrior
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Posted: 17:59 - 25 Nov 2019 Post subject: |
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to be honest i have given up. I have too many projects and just want to be able to ride my motorbike to work etc and get some practice in.
I have put it up on ebay if anyone is interested:
https://ebay.us/iilU7R?cmpnId=5338273189 ____________________ 1981 Honda CB125TB (With a T2 engine) |
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Easy-X Super Spammer
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Posted: 20:28 - 25 Nov 2019 Post subject: |
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That's a shame but sometimes you just have to call it ____________________ Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter |
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Old Thread Alert!
The last post was made 4 years, 125 days ago. Instead of replying here, would creating a new thread be more useful? |
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