DT125R FORUM

@Calum Ace build mate, I don't really know anything about On One bikes but that frame looks beautiful. And I've always liked eXotic, I ran a set of those rigid forks in a 26" fitness/road MTB I built a few years ago.

@kieran-hutchison Lots of ways of doing this but my preferred method is to get the caliper off the bike (but leave the hose connected for now), then gently pump the piston as far out as possible just using the brake pedal. Stuff some cardboard between the piston face and caliper body just in case the piston pops out suddenly and try and resist the temptation to grip the piston with mole grips etc. as this is a sealing surface. Keep an eye on the reservoir level as if it gets too low and air gets in, you might need to do a brake bleed just to get the piston out. And cradle the entire caliper in an old towel etc you no longer want to contain the spilt brake fluid. I've also used a foot pump before by stuffing one of those plastic airbed adaptors in the threaded hole where the hose attaches, this works well but you really do need to be careful and pump slowly as the piston will pop out suddenly, so you really need more than cardboard to stop it being damaged (and wear goggles ideally). In both cases it's better to pump the piston as far out as possible without it popping out, then edge it out with your fingers when it's almost free if you can.

It might be the case that a previous owner rebuilt the caliper with an aftermarket piston and seal kit. I bought an eBay DTR rear caliper rebuild kit once, cleaned the caliper completely including the seal grooves, put it together and bled it and there was a small dribble of brake fluid on the back of the pad on the piston side. Wiped it off and it came back several times, so I cleaned up the (old) genuine piston/seals and put them back in as I wanted to go for a ride that evening and it cured it, no issues for a couple of months whereupon I bought new genuine ones. Compared the seals, the eBay kit seals are slightly smaller in cross-section than genuine which is what causes them to leak.

@Calum Thanks bud

@tfsv8 Exactly the right thing to do holding off from fitting the big bore kit until you've sorted this, I'd start off taking a look at your jet sizes and compare these to what the Yamaha repair manual says they should be (Haynes managed to get their VM26SS '88 carb mixed up with their '89 onwards TM28SS so it's well worth getting a genuine Yamaha manual online).

I once bought a sub-5000 mile French import DTR in excellent condition which ran awful, on stripping the carb I found:

270 main jet fitted (stock TM28SS is either 210 or 240)
Float height about 5mm out ensuring the float bowl was constantly pretty much empty
One of the float bowl breathers blocked with silicone sealant
It also had a pattern coil which cause all kinds of running problems on DTRs, and the air filter element hadn't been cleaned in what looked like years (this went straight in the bin; a well-maintained £10 Yambits one is easily as good as a genuine Yamaha item)

It ran OK at low rpm but was asthmatic as soon as you tried to rev it and was pretty much unrideable as it was set up so a basically empty float bowl was trying to supply that fire hose main jet. As soon as I put the jetting/float height back to stock and fitted a genuine coil/new air filter it became well-mannered and went really well like a well-sorted DTR should. These are the kinds of modifications "Biwt me own bowek" type characters make to try and make 125s faster before heading off to Bike Night to brag about how the manufacturer didn't know what they were doing when they designed this bike so they had a few beers, went into their shed and finished the job.

@kieran-hutchison The waterpump drive gear could be broken as @Calum said, it's worth checking this.

The DT125R is a little prone to getting hot during serious off-roading. Compared to the twin radiator setup on the DT200R, the single rad with 2T oil tank opposite design is aimed more at youths messing about around town with perhaps a little bit of dirt riding occasionally. Near where I live there's a green lane which runs along a high ridgeline; to get onto it you have to go up a long steep unsurfaced hill where the farmer has added a lot of concrete speed humps to slow 4x4s down (which appears to have the opposite effect on dirt bikes). On three different DTRs I could literally watch my temp gauge go from 1/3 to 2/3 when enjoying myself up here, then when I reached the top where it was flat I'd go along in a high gear at low revs for a bit and it would quickly come back down.

If you're getting serious off-road it's worth looking at one of those Chinese pattern radiators which are about twice the thickness of the stock rad and look to bolt straight on. Also make sure your thermostat is working well (Haynes tell you how to test this) as one of it's functions along with the waterpump is to keep the water jacket around the cylinder pressurised which increases the coolant's boiling point (some competition bikes have restrictor plates in the cooling system to do this).

In the 1st instance I'd have a good visual inspection of your stock rad as the DTR is a bit prone to clumsy people bending the fins over when doing plug changes etc. which can reduce airflow by a fair bit. You can carefully use a thin screwdriver to straighten these and in extreme cases it can make the bike run cooler.

@mbmO8 This explains the YEIS box between the carb and reed valve better than I can:

https://global.yamaha-motor.com/stories/history/stories/0019.html

When working around that area it's not that difficult to remove as long as you have a decent pair of pliers to squeeze the clip on top of the reed block, just stuff a rag in the hole until you refit it. The one behind the carb on later bikes, I've never owned a DTR with one of these fitted so maybe someone else can help out explaining this? I see a lot of people blank these off with the lid off a Coke bottle.

@89dt125nick No worries bud When refitting the CDI to the oil tank, be sure to apply plenty of copper grease to the mounting bolts and brass inserts to prevent them corroding together (this is also a good idea for all the captive threads in the airbox) as if this happens it's almost impossible to get the bolts undone because they just spin round in the plastic. Common problem on MX bikes where the rad shrouds attach to plastic fuel tanks after a lot of pressure washing.

@89dt125nick Judging by the throttle cable splitter box and reg/rect (and your CDI being mounted on the 2T tank) I guess your DTR is a '99 onwards. The migration to the later electrical system wasn't completely smooth, for example I once owned a low mileage original French '98 4BL with 3NC electrics (CDI under the tank) but the two brass threaded inserts were present to mount the CDI at the front of the oil tank. Here are the cable routing diagrams for the '88 DTR, you might need to get a bit inventive with some items but hope this helps:

@mbmO8 Nice to hear bud, enjoy

@Hark_Ptooie I found with the Tecno expansion chamber (basically identical to the Athena) it fitted a lot easier using the genuine Yamaha rubber grommet and spacer on the upper mount. The ID of the spacer is quite large and allows a little more movement to line it up than the grommet/spacer supplied..

@Calum That one fits the shape of the DTRE well

@mbmO8 Depends what you want from investing in a tail tidy, if you want the back of the bike to look better you can make your own or if you're worried about the number plate falling off when greenlaning (a common problem as two plastic numberplate screws are fine for the road but not really up to serious off-road riding) you can reinforce the fitting of the numberplate with the stock setup.

I made this one back in the 90s before anyone had thought of manufacturing tail tidies, and my goal here was to make it look like one of the grey import bikes which were popular at the time and always had nicer lights/indicators than the equivalent UK-spec machine. What I did was to make a U-shaped piece of 1mm thick steel with the centre section the same width as the distance across the indicator mounts on the grabrail. The parts each side were about 30mm at the top tapering to 20mm at the bottom and I then mounted it fitted over the indicator mounts, sloping downwards at the same angle. I also made sure the full 260mm rear wheel travel was available without the rear tyre fouling the numberplate by removing the shock and lifting up the rear wheel with the bike on a MX bike stand. Although not visible in the pic there was enough space under the blue rear mudguard to fit one of those little oval standalone number plate lights, nicked off a Kawasaki Eliminator down the breakers IIRC. Cheap-ass mini indicators (but better ones are available these days) and taillight is one of those scaled down TS125R pattern lights and always worked very well:

https://www.denniswinter.com/off-road-c1/parts-c91/electrical-parts-c144/tail-lights-c473/raceline-enduro-3-motorcycle-tail-light-universal-fit-p258537

Or you can attach a piece of 2mm aluminium to the back of your full size numberplate using double sided tape to stop flying stones from breaking it, then use spacers to attach it to the rear mudguard in four places instead of two using M6 bolts, large washers and nyloc nuts (paint the heads black or yellow) for a really bombproof fitting. This looks stock from a distance and so doesn't attract the attention of Plod, the MOT man etc. but I've greenlaned/jumped DTRs with this setup and the numberplate never moved. And you get to keep your OEM rear light which is probably the best option.

I realise you asked for a simple tail tidy; neither of these options are simple but it's not going to be simple if you just buy one either. To make a decent job of doing the wiring you'll need a bullet connector kit (don't use those blue/red motor factors connectors) and there's no guarantee an aftermarket one will fit well without modification so you're better off approaching it with the goal of making the bike as good as it can possibly be from the viewpoint of you the owner. In reality nothing about DTR ownership is simple. There is an excellent passage in Zen and the Art of Motorcycle Maintenance by Robert M. Pirsig which goes something like "the craftsman and the work are changing together, and at the exact point where the work is as good as it can possibly be, the craftsman's state of mind is in a complete state of relaxation and contentment". He also talks about taking his (new) bike back to a main dealer to be fixed under warranty, where he observes the mechanics are basically a bunch of 25-going-on-13 adult toddler chimpanzees with OnRadioWuuuuun cranked up full volume (very much my own experience of working in the motorcycle trade). They end up making the bike worse, he takes it home and fixes it himself in about 5 minutes.

I hope I haven't put you off DTR ownership by writing this, if you buy a tail tidy online and fit it it will probably look good and work well but equally it can be very rewarding to sit down and design/make something that improves your bike and is unique.

@Calum Good shout re balancing the steel plates, just had a look in my Yamaha service manual and the clutch spring bolt tightening torque is 6Nm.

@Michaelashbrook Good time to invest in a 1/4" drive torque wrench if you don't already have one, these have become a lot cheaper in the last few years as so many things on bicycles now have torque settings: https://planetx.co.uk/products/jobsworth-pro-torque-wrench-set

@dominik22 I'd start by refitting the airbox snorkel and the stock silencer if you have one. My French '93 4BL ran very well running the jet sizes you mentioned (i.e 240 main) with either a full stock exhaust system or a Tecno expansion/DEP silencer combo but it didn't like the stock expansion/aftermarket silencer combination.

Sometimes the tailpipe can affect performance as the stock expansion chamber and silencer are designed to work together; if you change one it can alter back pressure and mess with the pressure waves going backwards and forwards. These evacuate exhaust gases from the cylinder, assist in drawing fresh mixture up through the transfer ports and act to keep the fresh charge from escaping straight out the exhaust port. I never thought the tailpipe alone would affect this but once I tried a brand new DEP silencer on my otherwise stock French '93 4BL with 3NC CDI; it immediately refused to rev beyond 9k. I rode it around for about an hour to eliminate wind direction etc., came home and refitted the stock silencer and straight away it revved to 10k+ again. This is only personal experience, I don't have access to a dyno or anything but it made a big impression on me. A Tecno expansion chamber would probably work well with that Athena silencer.

Tecno expansion is identical to the Athena apart from the clearcoat and under half the price. Only downside is the clearcoat melts around the header pipe and is difficult to sand off making your bike look like a Crème Brûlée. If I bought another one now I'd paintstripper it and paint it heatproof black before fitting it. Very good quality pipe for the money, gives a more usable mid-range hit than the DEP which delivers peak HP revs about 600rpm later.

https://www.ebay.co.uk/itm/253780922884?gclid=Cj0KCQjwurS3BhCGARIsADdUH5215jUowscJtBepB7NQYPYfR4AeBV1Gu63S4cHFVVEN8aPRotYawA4aAoc7EALw_wcB&_ul=GB&mkevt=1&mkcid=1&mkrid=710-53481-19255-0&campid=5339059258&toolid=10044&customid=Cj0KCQjwurS3BhCGARIsADdUH5215jUowscJtBepB7NQYPYfR4AeBV1Gu63S4cHFVVEN8aPRotYawA4aAoc7EALw_wcB

@Koltin As far as I know all pre-DTRE master cylinders are the same from 1988 until around 2004 so I'd start by comparing part numbers on Fowlers website, look up the part for say an '88, a '96 and your own bike:

https://www.fowlersparts.co.uk/?gad_source=1&gclid=CjwKCAjwl6-3BhBWEiwApN6_ks8FnxkMK8pUTlwAmDTt4wZ4GV5FlSqAj_zeubTOZF-qK69xd1CwVxoCpO4QAvD_BwE

@mbmO8 Try upgrading the stock headlight bulb before going the LED route.

The stock DTR headlight takes a P45T bulb (similar fitting to H4) and has AC lighting (i.e the power for the lights comes straight from the magneto without involving the battery) so you can run a 100/80W halogen bulb without flattening the battery unlike a lot of bigger bikes which run DC. The DTR’s actual light lens/reflector is the same as all Yamaha superbikes of the 80s like the RD500LC and XJ900, but Yamaha cheaped out and fitted a 45/40W candle to the DTR which is why lots of people don’t find it bright enough. 100/80W bulb lights up the roads/trails like a rally car and retains an MOT-friendly beam pattern. Once a year or two ago I met up with a bunch of guys greenlaning on modern KTMs and decided to tag along with them as it was getting dark; they couldn’t believe how much brighter my headlight was. Get this one:

https://www.ebay.co.uk/itm/161339938963?hash=item25909c1893:g:1~UAAOSwewJTn~QT&amdata=enc%3AAQAIAAAAwF8Gw72CnU%2FbU0Zeu1tjSRJFvfcr8SwbZT4fRnA6WLf6yF0iSX4F43bpTTUSgtfBlW1qXJSqMRtuS3Z1Luu%2FAD2VbsWrYvQrEc7oksN8VfDpaJHi6ZYW7zMtJnc%2F1be5np%2B6CZfap%2Frggb9cb01JyCQriOkPtIXXi8yWcKEn3mLr0%2Bhj6%2FoeZKr0o8Jl3vVA6Hka4%2F2xaD1awxGTbT2XEJFqjhxzyuYbuNe8sKHYOq%2Fho75%2FaGbmg%2FihQpqKGR%2B4kA%3D%3D|tkp%3ABk9SR6iwz8zLYg

@Calum Sorry to hear about your car bud. +1 for I'd keep hold of those extra clutch cover inserts if I were you, they look ace and are a part that can get rubbed/scratched just from riding so it would be cool to be able to just bung on a fresh one as and when.

@Bilbo9000 As @Calum says it looks/sounds like you've got the powervalve adjustment correct.

One thing I noticed when I bought some pattern powervalve cables from Yambits is the inner cables are very slightly the wrong length, meaning one of the adjusters only had like 4mm of thread engagement with the pulley housing when correctly adjusted; looking at your pic this could be the problem. I can't remember if the outers were too long but it's a common issue with pattern cables.

Genuine cables are better but they cost £20 each which is expensive for a short cable; they also don't retain lube very well as they're vertical, plus if you want to lube them properly you have to take them off, then readjust the YPVS every time. So this was my solution:

https://dt125r.co.uk/topic/2971/home-made-quick-lube-ypvs-powervalve-cables?_=1725612447259

@dominik22 Well you're doing better than me, once I was rebuilding a TDR250, thought I'd finished and then rode to my friend's house without connecting one of the carb warmer hoses! As you can imagine the temp gauge skyrocketed, luckily it wasn't far and we were able to top it up so I could get home.

@yeolderaver Only just seen you asked me about my bikes, back in 2021 I owned three French import DTRs, a '93 3NC (black/red Tecno/DEP pipe combo), a '98 3NC (black/red stock pipe) and a '98 3MB (blue/white knobbly tyres). The '93 I did a nut and bolt restoration so it basically looked new, then rebuilt the engine with a new crank, Athena 125cc top end, Zeeltronic ignition etc. Unfortunately I never got to ride it with the engine mods due to a few health problems but the new owner loves it apparently.

The '98 3NC I just cleaned up and rode for a few months, it had only done like 5000 dry miles from new so just needed a recommissioning. Although I did have to replace the oil seal behind the front sprocket as on my local green lanes, some extremely helpful person had left a woolly hat behind; this got sucked up behind the left engine cover and wound itself around the output shaft which knackered the oil seal. Lovely thing though and it turned heads everywhere it went.

The 3MB was owned by someone who used it for Paris commuting for over 20 years and it had racked up over 70000km; the highest mileage DTR I've ever seen anywhere. Despite this it was the fastest of the three, some of the steep hills near me there were places my (both full power) 3NCs would struggle but this just revved and revved. Amazingly when I replaced the head gasket I measured the bore and it was standard! I think the previous owner might have had so many rebores over the years they eventually had to just replace the barrel, French breakers are full of DTRs so you could probably get hold of a standard one quite easily.

I worked in the motorcycle trade when I was younger and that's kind of what led me back to the DTR 30 years later, I needed a Lockdown project and felt I had unfinished business with the bike industry because as a teenager/early 20s I found a lot of people I worked with quite dismissive and unhelpful, not sharing information etc.

During my recovery I realised I missed cycling more than motorcycling so this year I've restored a few mountain bikes, all mid-to-late 2000s Specialized Stumpjumpers. Eventually I want a 2005 (silver), 2007 (green) and 2008 (blue rims) in both large and medium so I can decide what year/frame size suits me best. The cycle industry can be pretty unhelpful as they're constantly trying to reinvent everything and convince buyers to get the latest thing (it's actually worse here than in the US) so it's quite a challenge hunting for parts all over the world but very satisfying.

Oh BTW talking of rear shock, I don't think the OEM one is rebuildable as it's under very high pressure like 300psi (Haynes tell you exactly where to drill a 3mm hole in it to release the pressure if you're throwing it away; WEAR GOGGLES) but the YSS DT125R shock is excellent. Also it's about 7mm shorter that the OEM shock which might help your daughter because when you factor in the linkage ratio it makes the rear of the bike sit about 21mm lower:

https://www.brooksuspension.co.uk/motorcycle-shock-absorbers/yamaha-dt-125-r-yss-mz366-shock-absorber-89-06

This vid shows why shocks are pressurised to stop the oil foaming:

https://www.youtube.com/watch?v=GBcRBOikb8c

@Calum Like your alloy (DT200R 3ET?) swingarm buddy. The plastic mud flap that protects the rear shock wears the (basically priceless) alloy swingarm away at the rear of the linkage bearing over time so it's worth installing something to prevent this (there's an Australian DT200R group on Facebook and almost every swingarm on there looks worn like this). Doesn't have to be expensive or flash, a lot of people with modern Huskies, KTMs etc. JB Weld a coin to the surface of the arm as they're prone to it as well. On mine I used the plastic sleeve which you get inside one of those boxes of sticky labels they sell in the post office cut open and cable tied on.

@Calum Nice job, twin rads look good as well.