DT125R FORUM

@lucasg.03 I wouldn't go for a Pipercross air filter element to be honest, the stock one is perfectly adequate if properly maintained. Interestingly I once bought a Twin Air DT125R element which was a bit too small to fit over the plastic cage properly, meaning the base wouldn't seat where it's supposed to seal against the airbox body.

I've also noticed some "tuners" on the DTR Facebook pages saying foam filter oil restricts power output. This is most definitely NOT the case; compare the surface area of the air filter element with the 28mm carburettor bore and there's no way a properly oiled filter could measurably reduce airflow.

You're better off getting 3-4 Yambits air filters which are just as good as stock but half the price; then establish a routine for cleaning and re-oiling them. Put the clean oiled ones in a plastic bag and you can quickly throw on a fresh one after every wash/off-road ride. Jet washing the bike and not changing the air filter/going for a short ride is a leading cause of ruined crankshafts on two-strokes, you only need like half a cup of water to creep in to knacker the mains/big end. And a clean air filter cuts down on a lot of other aggro; you see it all the time with RC car racing. Because a 1/8th buggy air filter is only the size of a 35mm film capsule it starts to affect throttle response after about 7 minutes on a dry dusty track. A lot of the guys at my local club used to try and play the Big I Am Tuning Wizard by endlessly twiddling the mixture screws but all they were doing was reducing the flow of fuel to match the reduced air flow (i.e less power). Whereas changing the air filter = getting your hands dirty; no cool points for the Bloke Down The Pub even though it means the engine just runs well and doesn't suck dirt right through the day.
Also the DTR airbox is poorly sealed where the carb-to-airbox boot meets the airbox (i.e downstream from the filter); it can be very helpful to seal this up with a product called Seal-All which is a petrol- and oil-resistant glue. You really need to remove the airbox completely to do this which means the shock needs to come out but this is easier than it sounds and you get to grease up the linkage bearings at the same time.

https://yambits.co.uk/dt125re-air-filter-p-9241.html

https://www.repairingproducts.co.uk/.../seal-all-gas-oil.../

@Strike78 Probably best you didn't fit the KTM headlight in the end.

Also, some LED bulbs fitted in lights not designed for them can disrupt the beam pattern and cause problems with the annual MOT test we have for roadworthyness in the UK, not sure where you're based but most countries in the world have something like this.

On the DTR one of the best modifications is to install a 100/80W halogen bulb which is a lot brighter than stock but doesn't cause an issue with the MOT test. I'm not too familiar with the DTX/RE headlight, @calum does it still require a P45T bulb like the DTR ort is it another fitting like H4 etc.? And do they have AC lighting like the DTR so they can still run a more powerful bulb without flattening the battery?

@Strike78 It certainly is! If you have an early DTR with the 3NC loom/CDI and 3-wire servo, by running a Zeeltronic and a 5-wire servo (more easily available) it's possible to install it without making any changes to your stock wiring loom. You can then keep the 3NC CDI and 3-wire servo and if you sell the bike or just want to return it to stock for any reason, it's just plug and play.

I'd just get it directly from Zeeltronic, Borut is very helpful and I ended up with quite a papertrail of emails after buying, he appeared genuinely interested in helping me gain a good understanding of ignition and powervalve maps (it's a lot more tunable if you run a 5-wire servo).

@Barron-1989 Yes white frame looking good :+1:

Get yourself on here for a 3-wire servo but be warned, it'll go crazy at the end of the auction, I'd be bidding in the last 30 seconds if it was me:

https://www.ebay.co.uk/itm/336567587789?_skw=Yamaha+DT125R+YPVS+Power+Valve+Servo+3+Wire+3MB-85820-00-00&itmmeta=01KQT8H9E0R37E9VYX7EPS2BN6&hash=item4e5cfdd3cd:g:bfgAAeSwr9dp-JC5

Other than that start looking around French and German breakers online as they're full of DTRs. The KTM LC2 125 trail bike (kind of an Austrian DTR) used the 3MB DT125RE engine and electrics and the 3-wire servo is the same so search for part numbers:

3MB-85820-00 (Yamaha)
51137095000 (KTM) https://www.trevorpopemotorcycles.co.uk/index.php?main_page=ktm_fiche_finder&model=112684&group=C96511304_080010&cat=3&bike_name=1998 125 LC2 100 (D)&section=1&groupname=CYLINDER HEAD EURO 125 96

I once purchased a number of BNIP LC2 servos which had both part numbers printed on the label and they were blatantly 3MB Yamaha 3-wire servos, sadly now all gone but if you're lucky you might find some somewhere.

Re PV pulley and cables, the pulley and housing is identical to all other Yamaha '80s/'90s two-strokes apart from the RD500LC so any pulley and housing from an RD350YPVS, TZR/TDR/R1-Z250 or TZR125/TZR125R/TDR125 should fit (they're all stamped 29L which is the YPVS350 model code).

I wouldn't recommend Yambits PV cables as the outers are very slightly the wrong length meaning you only get like 2-3mm thread engagement in the pulley housing with the PV adjusted correctly. Genuine cables are worth every penny or if you're into lubing cables after every wash like me, you can make your own here:

https://dt125r.co.uk/post/28693

@Hoolies Yes the balance shaft only has one gear, assuming it's the same as the DTR balance shaft gears you just need to ensure the dot on the balance shaft gear is aligned with the dot on the crankshaft gear.

@Hoolies @beng1968 It does sound like the balance shaft gears aren't aligned, I didn't even know the pre-DTR engines had a balance shaft to be honest. This is where I went to find out, DT125LC MkIII is (I think) the closest I could think of, might be worth ordering items 24, 26 and 27 if you need to remove and refit the balance shaft gear:

https://www.fowlersparts.co.uk/parts/4047858/dt125lc-1hr-1987-999/crankshaft-piston

@Elan-n Considering your symptoms the only thing I can really think of is incorrect float height; the only reason I'm suggesting this is, Haynes made a big mistake and got their VM26SS (round slide '88) float height (21mm) mixed up with the later TM28SS which should be 15.5-16.5mm. A lot of people read this and through no fault of their own, set their TM28SS float height to 21mm which of course means there's (a lot) less fuel in the float bowl at any given time. This could explain why the bike's pulling well when you wind on the power gently, but struggling when you apply full throttle straight away. Appreciate the plug colour might reflect a lean running condition but on the other hand it might not if you're experimenting with a lot of different engine speeds/throttle openings as a plug chop is only of any real use when done precisely at a specific engine speed according to a lot of two-stroke tuners.

Other than that, intermittent problems are often something simple; I'd go right through the electrics and clean up/WD40 every connector for starters. A corroded block connector somewhere can throw up all kinds of head-scratching like this. Do the handlebar switches, sidestand switch and the electrical part of the ignition switch (these usually have small hole for this purpose) as well, really blast the WD40 in so it fizzes and bubbles out of all the gaps and flushes out the corrosion as the exposure to all weathers on a bike is a harsh environment for a switch. Throw old towels over the wheels while you do it to protect the tyres and brakes.

I once lost the spark altogether on all 4 cylinders of a Suzuki GSF400 Bandit, it was a Japanese import with complicated V-Tec variable valve timing and no service information available in the UK so it caused me a measure of panic as you can imagine. The parts guy at the local Suzuki dealership simply said "a set of plugs (£10 each in 1998) will get it going". I thought you've got to be a genius to make 4 NGK plugs fail at exactly the same instant and so declined his offer. A bit later I was cleaning it and saw a relay under the seat (I still to this day don't know what it was for, poss. sidetand switch-related or something) which had some blue copper sulphate-looking corrosion oozing out of it, so I cut it open with a small hacksaw and found one of the tracks in the PCB had corroded through. Half an hour with the soldering iron, I bridged the split with a tiny wire out of one of those 8-pin landline phone connectors and it started up and ran perfectly.

You're going in the right direction with this, if it runs really well some of the time I don't think its jetting related.

@reudtr88 The seller is right, the spacers and caliper bracket are narrower than the DT125R versions.

The bench mock-up in the pics above comprised a 3ET DT200R swingarm, caliper hanger and spacers mated to a DT125R hub. As you can see the 428 sprockets lined up quite well (I also had to use a 3mm thick M20 washer between the caliper hanger and swingarm to get it as good as it could possibly be with the items I had to hand).

@kepirok I wouldn't use anything metallic like a piece of wire or drill bit to unblock the powerjet as it will be a very specific size. Did you try soaking it in alloy wheel cleaner? Check it out here from 6:52 onwards:

https://www.youtube.com/watch?v=-1ETYWSJNnM

@Calum Thanks bud, yes the TDR250 was great fun and released at a time when no-one in the UK really knew what Supermoto was. Getting the TZR250 wheels to fit was a popular mod at the time but quite difficult as there's no bearing available anywhere in the world with TZR front wheel OD and TDR spindle ID so I had to get a local machinist to make up some very thin sleeves which were carefully pressed into the TZR wheel to accomodate a different sized bearing. At a track day I met someone with another one who'd laced his OEM rear rim to the front hub to run a 120/17 size tyre, then fitted an even wider rim to the rear hub with a 150 size tyre on the back. It looked a lot more subtle than the 3-spokes and I think if I could do it all again that's what I would do.

@rob-tdr is correct, all the '90s two strokes are unbelievably expensive now, I've seen well-sorted TDR250s going for £8k+ on eBay.

@kepirok Hi bud,

I'd be looking at repairing your original carb or trying to source a replacement, if your cylinder is slightly ported as you say it shouldn't make much difference. Back in the day two-stroke tuners like Stan Stephens etc. used to wring a lot more power out of these engines, very rarely suggested a carb swap unless going fo a full race, rebuild-every-few-hours spec and in a lot of cases even recommended retaining the stock jetting. If your stock carb is really scabby try soaking it in alloy wheel cleaner for 24hrs.

The OEM DTR carb also has a slightly angled float bowl which means it's horizontal with the carb installed, a useful feature due to Mikuni designing the TM28SS specifically for quite a narrow range of Yamaha bikes. It can be a bit expensive to get one in good condition but the time and aggro saved (your bike will just work) is well worth it. The biggest problem with the TM28SS is the air screw seizing but this can be prevented by a smear of copper grease on the threads when installing it in the carb body (it's also worth doing this on all the other carb screws which retain the float bowl, carb top etc), and always spraying the entire engine/carb/radiator area with WD40 after washing the bike (get the 5 litre size with free trigger spray from a motor factors).

I think your Athena exhaust is the same as the Tecno expansion chamber which I've run on stock carb/jetting with good results. Is your ignition a Zeeltronic? If so they're very helpful and will probably tell you which ignition map works best with the stock carb if you email them.

@Rob-TDR Welcome to the Forum, that is a beautiful original TDR125R. They seem to be very rare and I prefer them to the TDR125 we received in the UK which looks like a TDM850.
Was the TDR250 sold in Italy? If so I think it would be easier to get one of those and keep your Lightburner original as it will be worth more as time passes.

The TDR250 is absolutely insane, I owned three of them in the 90s and they gave bikes four times their size a run for their money due to Supermoto agility and acceleration up to 70-80mph as fast as the 750s of the day. Everyone who rode one of mine came back unable to stop laughing, saying these things should be banned etc. Trust me, a TDR250 will always have enough power...

Benvenuto nel forum, quella è una bellissima TDR125R originale. Sembrano essere molto rare e le preferisco alla TDR125 che abbiamo ricevuto nel Regno Unito, che sembra una TDM850.
La TDR250 veniva venduta in Italia? In tal caso, penso che sarebbe più facile procurarsene una e mantenere la tua Lightburner originale, dato che il suo valore aumenterà col tempo.
La TDR250 è assolutamente pazzesca, ne ho possedute tre negli anni '90 e davano del filo da torcere a moto quattro volte più grandi grazie alla loro agilità da supermoto e all'accelerazione fino a 110-130 km/h, veloce quanto le 750 dell'epoca. Tutti quelli che hanno guidato una delle mie sono tornati a casa ridendo a crepapelle, dicendo che queste moto dovrebbero essere vietate, ecc. Credimi, una TDR250 avrà sempre potenza a sufficienza...

@Elan-n Don't worry about it, I've done a lot worse! Sometimes you can be so close to the thing you're trying to fix it's easy to miss something. The main thing is you're moving forward :+1:

@JOHNES No worries bud :+1: I'd still stick with an OEM coil if you can TBH, it's just one thing you can definitively rule out during the fault-finding process of elimination.

@JOHNES It sounds like the annoying spring steel retaining clip that holds the final delivery pipe onto the reed block; depending on how it was fitted, sometimes the end of these (which you need to get a tiny flat-bladed screwdriver underneath to remove) can be hidden and difficult to get to. It does give the appearance of the pipe fitting inside the reed block.

The pipe also sticks to the stub on the reed block over time so once you've got the clip off, try pushing it a little further on first to dislodge it. A clear oil delivery pipe kit from Yambits makes the bleed process a lot easier and gives at-a-glance peace of mind when riding, also comes with new clips:

https://yambits.co.uk/dt125r-oil-line-kit-clear-p-26778.html

Not sure why they don't list this for the DTRe, this was in the DT125R section but should fit.

@JOHNES Welcome to the Forum buddy, unfortunately those aftermarket ignition coils cause all manner of problems on the DTR/DTRe. New genuine from Fowlers (or your nearest Yamaha stockist if you're not in the UK) is worth every penny.

Are you sure it's the actual coil that is causing the problem, or could it be the HT lead? They break own on DTRs causing this exact problem. The actual coil is very good quality so it's well worth fitting a new lead. On early DTRs you can cut off the very top of the coil's outer case where the lead pushes in with a junior hacksaw, pull out the old lead and solder the new one to the coil output for a really good connection. Then re-waterproof using Shoe Goo and electrical tape. Looks messy but no-one can see it under the tank, and you should notice a performance increase as the leads deteriorate over time. Much better option than just buying a new pattern coil as these often have different specs to OEM which can cause other issues. Fit a new NGK cap while you're there, try to get the type that's moulded into a single piece of rubber.
I had a high-rpm misfire once, after trying everything else we replaced the HT lead in the manner described above which took around 1 hour on a summer's day so the engine was neither stone cold nor up to operating temperature when I took it for a test ride. It wheelied out of the driveway without me even trying, and I couldn't believe how much better the performance was at all engine speeds. Made a big impression on me as I was 17 at the time and I'd spent practically a weekend trying to fix the bike and getting nowhere.

@DTGREENLANER I'd say that's a dry bearing inside the servo somewhere, I think they can be taken apart and the gear train serviced. Never done one myself but it's pretty much a scaled-up RC car servo, just take your time and lay everything out in the order you removed it and you should be all good. Southeast Asia is full of DTRs, DT230 Lanzas etc. and some of those guys repair the servos quite often.

@rhodes5150 Pretty certain this is the one I used to run on the DTR, sticks out slightly more than original but the shape means it fits around even the more bulky DTRe engine cover:

https://www.ebay.co.uk/itm/363368465294?_skw=apico+YZ125+gear+lever&epid=8012759732&itmmeta=01KMDMK6F9YWWAGHQM3VVJ6WB4&hash=item549a72c38e:g:hPUAAOSw3gNggHtZ&itmprp=enc%3AAQALAAAA8GfYFPkwiKCW4ZNSs2u11xDUERQmESMU2CAlX1DcPGGjtQDWXKIOkMFlCI220%2FOghQ4QLH4yJSNvuMwJ6HtAxporHqFfRmGvzIVqQiIllh%2BKwfnrqpjXewQ7ymgSLsNdzsz32dKsKHRQckjfpclFoIXvLLsWkUu%2BdCjXGTj60n10tq0t8bgR%2BXtadCqU0hzv09UoU8ySJzIBIAWoLyKWQakbH0AINkprvtCDcGFBr5ahx7RWbK9OpZPk2z%2BX7%2FUNs4f3un%2FMQVgwueCuXdb2NDSpjumtBFuxFoGzhqF7QmVGJs6ODVThIgUhxBcNhhbS1g%3D%3D|tkp%3ABk9SR5rozLSjZw

@Elan-n Agree with @calum about the Zeeltronic, I enjoyed the process of installing mine and making it look as stock as possible.

Re jetting, I think I'd be contacting Romeu Henriques, tell him about your other mods (intake spacer dimensions etc.) and see what he says. Everyone speaks very highly of his exhaust systems so he will probably have enough knowledge to plug the numbers into some two-stroke tuning equations and help you out.

@Elan-n You can make your own using stainless MTB gear cables, use the inline cable oilers as well and you can quickly re-lube them after every wash:

https://dt125r.co.uk/post/28693