Bought a blue RD125 new in August 77 (still remember the reg:ACA 346S) , did 18000 miles in 18 months (before selling and buying a TriumphTiger 650). Apart from servicing I only had to de-coke the exhausts after about 12k - never let me down. 45yrs later I've just bought another, needs a fair bit of work but, now retired, so have time to get it back on the road. I've owned quite a few bikes over my lifetime but, the Yam was special for many reasons.
Expert thorough painstaking diagnostics , I had one of these beautiful little bikes some 30 years ago in metallic blue, bought for £50 with the same troublesome reliability .Replaced the same electronics with new/ old stock parts from an old established Yamaha dealer and remained reliable for remaining ownership. I see its still exists and is taxed and wish I'd hung on to it !.
For me there is nothing that sounds as good as a twin cylinder two stroke with spannies on! That RD 125 sounds so sweet. I hade a yellow RD 250E in the early 80's and that sound takes me straight back, I immediately want to get out again on a RD! I had even planned on getting a RD125 exactly like this one when they were talking about the new 125 learner laws, at the time, but passed my test in time. Arrrrr those were the days, rose tinted spectacles and all!
Nice work sir, people moaning about your description of the amount of work gone into this fab bike but it’s info like this that helps others trouble shoot there problems.. well done and I bet the owner is super happy and reliable 🙌
I had an RD200 which developed a similar problem (dropping to one cylinder) just before I part exchanged it for a 1981 Z550A2. It was running fine when the dealer agreed a price, so he was non the wiser when I dropped it off a week later and rode away on my shiney new 550. I tried to get it running properly again beforehand, but nothing I did made any difference. The RD200 had a combined generator/electric starter, which didn't seem to work well in either capacity.
Passed my test on mine in 1979. The examiner said I will not see you all the time but you will not know when! He was running round the block at the test centre in Hornchurch, Essex. Great little bike as long as you kept on top of the points adjusment etc. Great sound even on standard pipes.
I've thought about getting a bike that needs an issue sorting out but this video just goes to show that when you have a problem its a process of elimination that can take ages and cost multiple amounts of cash to get to the main problem. Obviously previous experience and some proper testing equipment doesn't go amiss. Anyway's a good job and some knowledge about electrical systems and how they operate.😎👍🎸🍷🇬🇧
This was a great video! I've done a rebuild on a 1972 R5C and having much the same problem with the spigot mount Mikuni carbs (much like the ones shown on your bike here). They were carefully rebuilt but I'm wondering if I got the right parts as you've discovered. Same problems with way over rich, over oiling, fouled plugs. Work to be done for sure, but this video helps. I'll check out Yambits.
There are several "gotchas" that can affect various Yamaha twins, that I came across in the course of doing motorcycle repairs in the 1970s and 80s. It is possible to interchange the left and right throttle slides but they will be back to front with the cutaway facing the engine. This causes extremely rich mixture. It is possible to fit the pistons back to front, so that large amounts of exhaust gas are drawn back into the crankcases (this is possible on the single cylinder models as well). The engine will start easily and run perfectly smoothly, but will give about 15 per cent of the normal power output. If you roll up some tools in a piece of cloth and put them under the seat, it is possible that they obstruct the air intake and cause very rich mixture. I have also seen a problem with a roll of tools under the seat of an MZ Supafive, which did not block the intake but did dent the voltage regulator in a way that jammed the contacts closed and caused light bulbs to fail and the battery to boil dry. On the RD125 twin I have seen one that had very little power partly because the silencer baffles were bunged with carbon and partly because the points gaps were wrong leading to the ignition timing also being wrong. The owner had not dared check or adjust the points because he knew the setting was very critical. On the RD200 and RS200 (with electric starting) the ignition has a centrifugal advance mechanism, and the centrifugal weights must be held in the fully-out position while you set the timing to 1.8mm BTDC. I have repaired one of these after it melted a hole in one of the pistons because an official Yamaha dealer set the timing with the weights in the inward position. On the early RD250 and RD350 (A and B models) the electrical system can suddenly die completely if the battery voltage gets low for any reason. The battery has to be above a certain voltage in order to magnetise the alternator rotor (via a pair of brushes and slip-rings) sufficiently for the alternator to charge the battery. The 125, 400 and later 250s have a permanent-magnet alternator and the RD/RS200 have a DC dynamo that doubles as a starter motor.
I recently had my kawasaki triple overhauled. Well, it was meant to be just a simple rebuild, checking the output from the stator, possibly a rebore.... £3,000+ later, and it needed a new crank, pistons, wiring loom, rear wheel rebuild, gear selectors, some rechroming, new seat cover, and custom made sleeves to fit to the inlets on the rear of the cylinders where the carbs clamp on, you couldn't tighten the carbs properly (potentially letting air get in), and the oil pump wasn't giving the same amount of oil to each cylinder either. Two strokes are theoretically so simple to work on, but they cunningly wear out different parts simultaneously, they'll still run... until they don't, and then it's never one thing you have to fix. That RD sounds perfect, and what I like about the 125s is you can thrash them without having to do silly, licence endangering speeds. I have a DT125R too, and it's my favourite bike.
Had one of these bikes bout 1980, got used and came with expansion chambers on it & needed to rev the nuts off it (sounded great) sourced a set of std pipes for fitted em WOW totally different bike smoother in every way, dint haf to rev so hard, so spannies on the road nah keep em std..... 'Ull' east yorkshire.
So many pipes for these back in the day! These just seemed to sound well on any of them but were pretty anti social on the bean can Microns, sounded ace though 😆
I had a similar bike in 1984 (1978 version) the dealership said it was fine, but it was lacking power, so i took to a local mechanic to decoke it, whilst doing the job, he noticed issues with the crankshaft, i told him i only had a month left on the warranty, so he advised don't put oil in it, basically blow the engine, which i did, the dealership had to fit a new crankshaft and a total engine rebuild under the warranty, but i made sure i never mentioned my local mechanic, after the rebuild it was a totally different bike, the full 17bhp, nearly 80 mph on the flat roads.
Yup you are right cant beat that sound, I had the Red rd 125 dx in late 70s, I took out the muffler tube and put a length of bent copper pipe sounded good too ah memorys
Awesome my first bike was a 125 twin Yamaha 🤗 I could run it backwards, if I swap the leads and roll start it, bit tricky to ride like that, but it was not an RD too old 73 AS3.
Well the owner has been out and covered about 60 trouble free miles and said it was riding like a new bike, but then reported back to me it's fouled the right hand plug and looks like it's lost spark on that cylinder so some more investigation to do. Hopefully it's not down to the charging through the modified reg/rec but we'll try to find out soon.
I had an old Yamaha twin 180 when I was younger and when the battery got low it would run on one cylinder.. finally put brushes in it and undercut the commutator
Yes the RD200 genny\starter does cause trouble, but most of it is down to the old mechanical relays in the control box. I worked with a company to develop a solid state unit to replace them and that made the whole system much more reliable and gives great charging, sadly about 30 years too late 😬
Kind of! Most Japanese manufacturers quote engine BHP, which would be measured at the crank, as we do the testing at the rear wheel there's an expected loss of approx 15% depending on the bike, so in this case 14.5 bhp isn't really too bad 😁
It was on "standard" jetting when it first came in, and as far as we know has always had standard airbox. The pipes on their own don't need any changes on main jet from stock settings (although I'd always check that on after fitting!).. The issues come from the Keyster carb kits, they're not well listed related to the different models, the 125's going through the carb models have significant changes through the years, main jets go 82 to 94, slide cutaway changes from 1.5 to 2.5 and air jet from 2 to 2.5, pilots range from 40 to 44, nozzles change through N30 to N80 so 1 carb kit doesn't suit all models and if fitted to the wrong model runs rich and fouls cylinders/plugs etc. The only kit I've found that's genuinely correct for the later models especially is the one Yambits supply as they're looked into all the changes and created the kit to suit.
Hi, we're in Thirsk, Nth Yorkshire. A lot of bikes come into us via courier, it's usually the cheapest way as they can share a journey with another bike. If you want to have a chat about having the 400 looked at please check my webpage dbmotorepairs.co.uk
I had a RD200 from new. It was constantly oiling up spark plugs, constantly in the workshop, the mechanic's said there was no problem, it was my fault because I was not revving the engine enough! A couple of weeks after the guarantee run out it started making a knocking noise from the engine. The "mechanic's" said I should try to sell it as soon as possible (the bike was only 2 year's old and less than 2 thousand miles) because the engine was knackered. Within days of this the noise from the engine made it impossible to ride. Had it repaired (at a different mechanic) it needed a new Crankshaft, new pistons, rebore, and new bearings. I complained to Yamaha UK and they said the bike was outside the warrantee period and there was nothing they could do. In the forty plus years since then I have owned many bikes and none of them have even come close to causing as much trouble as that Yamaha did. I did learn from that experience, never buy brand new and never buy a Yamaha!
Bought a blue RD125 new in August 77 (still remember the reg:ACA 346S) , did 18000 miles in 18 months (before selling and buying a TriumphTiger 650). Apart from servicing I only had to de-coke the exhausts after about 12k - never let me down.
45yrs later I've just bought another, needs a fair bit of work but, now retired, so have time to get it back on the road.
I've owned quite a few bikes over my lifetime but, the Yam was special for many reasons.
Expert thorough painstaking diagnostics , I had one of these beautiful little bikes some 30 years ago in metallic blue, bought for £50 with the same troublesome reliability .Replaced the same electronics with new/ old stock parts from an old established Yamaha dealer and remained reliable for remaining ownership. I see its still exists and is taxed and wish I'd hung on to it !.
For me there is nothing that sounds as good as a twin cylinder two stroke with spannies on!
That RD 125 sounds so sweet.
I hade a yellow RD 250E in the early 80's and that sound takes me straight back, I immediately want to get out again on a RD!
I had even planned on getting a RD125 exactly like this one when they were talking about the new 125 learner laws, at the time, but passed my test in time.
Arrrrr those were the days, rose tinted spectacles and all!
Just love the sound of a ring a ding machine. I need to get one to put in the garage.
Nice work sir, people moaning about your description of the amount of work gone into this fab bike but it’s info like this that helps others trouble shoot there problems.. well done and I bet the owner is super happy and reliable 🙌
Lovely classic bike,
I never had the 125cc but two of my friends had them great bikes I did have the 200cc and the 400cc great days .
I had an RD250 and 350. Happy days.
I had an RD200 which developed a similar problem (dropping to one cylinder) just before I part exchanged it for a 1981 Z550A2. It was running fine when the dealer agreed a price, so he was non the wiser when I dropped it off a week later and rode away on my shiney new 550. I tried to get it running properly again beforehand, but nothing I did made any difference. The RD200 had a combined generator/electric starter, which didn't seem to work well in either capacity.
Passed my test on mine in 1979. The examiner said I will not see you all the time but you will not know when! He was running round the block at the test centre in Hornchurch, Essex. Great little bike as long as you kept on top of the points adjusment etc. Great sound even on standard pipes.
Not bad for a chicken chaser..Nice touch with the allspeed pipes...respect 😊
I've thought about getting a bike that needs an issue sorting out but this video just goes to show that when you have a problem its a process of elimination that can take ages and cost multiple amounts of cash to get to the main problem. Obviously previous experience and some proper testing equipment doesn't go amiss. Anyway's a good job and some knowledge about electrical systems and how they operate.😎👍🎸🍷🇬🇧
Thanks for sharing your hard won knowledge on all those faults, really appreciated.
This was a great video! I've done a rebuild on a 1972 R5C and having much the same problem with the spigot mount Mikuni carbs (much like the ones shown on your bike here). They were carefully rebuilt but I'm wondering if I got the right parts as you've discovered. Same problems with way over rich, over oiling, fouled plugs. Work to be done for sure, but this video helps. I'll check out Yambits.
@@steamboy101 if you need any info please feel free to ask.
This channel is the relief after watching Mr vintage melt throttle cables in 10 seconds
Well done, worth the effort i really like your RD jealous of your disc brake lol.
There are several "gotchas" that can affect various Yamaha twins, that I came across in the course of doing motorcycle repairs in the 1970s and 80s. It is possible to interchange the left and right throttle slides but they will be back to front with the cutaway facing the engine. This causes extremely rich mixture. It is possible to fit the pistons back to front, so that large amounts of exhaust gas are drawn back into the crankcases (this is possible on the single cylinder models as well). The engine will start easily and run perfectly smoothly, but will give about 15 per cent of the normal power output.
If you roll up some tools in a piece of cloth and put them under the seat, it is possible that they obstruct the air intake and cause very rich mixture. I have also seen a problem with a roll of tools under the seat of an MZ Supafive, which did not block the intake but did dent the voltage regulator in a way that jammed the contacts closed and caused light bulbs to fail and the battery to boil dry.
On the RD125 twin I have seen one that had very little power partly because the silencer baffles were bunged with carbon and partly because the points gaps were wrong leading to the ignition timing also being wrong. The owner had not dared check or adjust the points because he knew the setting was very critical.
On the RD200 and RS200 (with electric starting) the ignition has a centrifugal advance mechanism, and the centrifugal weights must be held in the fully-out position while you set the timing to 1.8mm BTDC. I have repaired one of these after it melted a hole in one of the pistons because an official Yamaha dealer set the timing with the weights in the inward position.
On the early RD250 and RD350 (A and B models) the electrical system can suddenly die completely if the battery voltage gets low for any reason. The battery has to be above a certain voltage in order to magnetise the alternator rotor (via a pair of brushes and slip-rings) sufficiently for the alternator to charge the battery. The 125, 400 and later 250s have a permanent-magnet alternator and the RD/RS200 have a DC dynamo that doubles as a starter motor.
I recently had my kawasaki triple overhauled.
Well, it was meant to be just a simple rebuild, checking the output from the stator, possibly a rebore.... £3,000+ later, and it needed a new crank, pistons, wiring loom, rear wheel rebuild, gear selectors, some rechroming, new seat cover, and custom made sleeves to fit to the inlets on the rear of the cylinders where the carbs clamp on, you couldn't tighten the carbs properly (potentially letting air get in), and the oil pump wasn't giving the same amount of oil to each cylinder either.
Two strokes are theoretically so simple to work on, but they cunningly wear out different parts simultaneously, they'll still run... until they don't, and then it's never one thing you have to fix.
That RD sounds perfect, and what I like about the 125s is you can thrash them without having to do silly, licence endangering speeds.
I have a DT125R too, and it's my favourite bike.
Had one of these bikes bout 1980, got used and came with expansion chambers on it & needed to rev the nuts off it (sounded great) sourced a set of std pipes for fitted em WOW totally different bike smoother in every way, dint haf to rev so hard, so spannies on the road nah keep em std.....
'Ull' east yorkshire.
Great bike, had a blue one in 84 with Allspeeds on, sounded great.
So many pipes for these back in the day! These just seemed to sound well on any of them but were pretty anti social on the bean can Microns, sounded ace though 😆
Yes definitely, great diagnostic work by the way.
I had a similar bike in 1984 (1978 version) the dealership said it was fine, but it was lacking power, so i took to a local mechanic to decoke it, whilst doing the job, he noticed issues with the crankshaft, i told him i only had a month left on the warranty, so he advised don't put oil in it, basically blow the engine, which i did, the dealership had to fit a new crankshaft and a total engine rebuild under the warranty, but i made sure i never mentioned my local mechanic, after the rebuild it was a totally different bike, the full 17bhp, nearly 80 mph on the flat roads.
My bro bought a red one in 1980. Great days.
Yup you are right cant beat that sound, I had the Red rd 125 dx in late 70s, I took out the muffler tube and
put a length of bent copper pipe sounded good too ah memorys
I had one of these it was red and white brilliant little bikes
These were super-fun back in the day !
I had one these were fun lovely smell from the exhaust fast and fun to ride
Awesome my first bike was a 125 twin Yamaha 🤗 I could run it backwards, if I swap the leads and roll start it, bit tricky to ride like that, but it was not an RD too old 73 AS3.
That sound😊
You always check the fundamentals first yes the charging circuit is one of the first things I Check -in any bike I'm unfamiliar with
I’d love to potter that around town this summer 😎💨
Nothing like playing for time is there,
Good video. Really interesting. My question how much has the work cost what you have done to it. Nice bike
had a 125 dx twin moto martin pipes on it great little bikes
I kept thinking "why do you keep taking this bike to your taxi driver?"......then I sussed you were saying Mick Abbey........
😁 aye you've got to do a bit of translation sometimes!
125 thrashbox is what I heard them called 😂
That thing is so bad ass is it for sale
Well the owner has been out and covered about 60 trouble free miles and said it was riding like a new bike, but then reported back to me it's fouled the right hand plug and looks like it's lost spark on that cylinder so some more investigation to do. Hopefully it's not down to the charging through the modified reg/rec but we'll try to find out soon.
I had an old Yamaha twin 180 when I was younger and when the battery got low it would run on one cylinder.. finally put brushes in it and undercut the commutator
Yes the RD200 genny\starter does cause trouble, but most of it is down to the old mechanical relays in the control box. I worked with a company to develop a solid state unit to replace them and that made the whole system much more reliable and gives great charging, sadly about 30 years too late 😬
Cool dude 💯🤘🏼
I just got an old twin jet 100
I want it!!
Great and informative vid 👍 I did think these were around 16bhp from the factory, or is that just wishful, rose tinted thinking?
Kind of! Most Japanese manufacturers quote engine BHP, which would be measured at the crank, as we do the testing at the rear wheel there's an expected loss of approx 15% depending on the bike, so in this case 14.5 bhp isn't really too bad 😁
got to make yr cut
What with the pipes, it was probably jeted for k&n pod filters, and the original air box refited.?
It was on "standard" jetting when it first came in, and as far as we know has always had standard airbox. The pipes on their own don't need any changes on main jet from stock settings (although I'd always check that on after fitting!).. The issues come from the Keyster carb kits, they're not well listed related to the different models, the 125's going through the carb models have significant changes through the years, main jets go 82 to 94, slide cutaway changes from 1.5 to 2.5 and air jet from 2 to 2.5, pilots range from 40 to 44, nozzles change through N30 to N80 so 1 carb kit doesn't suit all models and if fitted to the wrong model runs rich and fouls cylinders/plugs etc. The only kit I've found that's genuinely correct for the later models especially is the one Yambits supply as they're looked into all the changes and created the kit to suit.
Hi how far are you from me I live ip28 7qa I’ve got a rd400f 1979 which is a pig to start and ALLSPEED exhaust system on it
Hi, we're in Thirsk, Nth Yorkshire. A lot of bikes come into us via courier, it's usually the cheapest way as they can share a journey with another bike. If you want to have a chat about having the 400 looked at please check my webpage dbmotorepairs.co.uk
I have the same bike 1980 model
That thing sounds amazing.
Hy there, just a quick question. What kind of air filter do jou use? I have the same bike, fully restored but cant find the correct air filter. Thanks
Try Yambits, double check first for your model but I think it's this one: yambits.co.uk/rd125-1980-air-filter-p-62696.html
🏍👍👍
I had a RD200 from new. It was constantly oiling up spark plugs, constantly in the workshop, the mechanic's said there was no problem, it was my fault because I was not revving the engine enough!
A couple of weeks after the guarantee run out it started making a knocking noise from the engine. The "mechanic's" said I should try to sell it as soon as possible (the bike was only 2 year's old and less than 2 thousand miles) because the engine was knackered.
Within days of this the noise from the engine made it impossible to ride. Had it repaired (at a different mechanic) it needed a new Crankshaft, new pistons, rebore, and new bearings.
I complained to Yamaha UK and they said the bike was outside the warrantee period and there was nothing they could do.
In the forty plus years since then I have owned many bikes and none of them have even come close to causing as much trouble as that Yamaha did.
I did learn from that experience, never buy brand new and never buy a Yamaha!
Is the owner called Kev?
Yes lad
Yes lad
@@billybarr7443 Yeah, I spoke to him last night about it.
14.5hp, it should be 17hp at least.
Laughing at the cheap and nasty Japanese electrics from the saddle of my Jawa 350TS 😀