DT125R FORUM

I'm a bit of a Japanese Auction addict, whilst picking up parts for another project I found these gems.

As I designer I love automotive brochures and presentation of the original product. These seem to be extremely rare and the Japanese material of the time the most compelling,

Check out my Flickr for more: https://www.flickr.com/photos/brodie-dart-pieces/

First up the original release of the Yamaha DT200WR '1991

Was it better than the Kawasaki KDX200? It's an odd motorcycle.

1992 DT200WR

1993 DT200WR

1994 DT200WR

Note Yamaha dropped the curved Kickstand in '94, not the easiest to fit onto a DTR, but an amazing upgrade if you can find one!

Be Riding Friends?

Finally, the JDM DTR. Not as special as you might of thought. The 3FW is the Japanese version of the DT125R. They came standard with Alloy wheels and Electric start sprocket cover and wiring.

The biggest note, pretty sure all 3FWs came with the original Mikuni VM26ss carb, so we didn't miss much..,

1991 DT125R - SUPER TRAIL...,

1994 DT125R - SUPER TRAIL

1999 DT125R - SUPER TRAIL

90s forever.

@rogering Using a Capacitor is just fine.

I ran one for over 2years. If you are woods riding/ trail stuff then I highly recommend keeping the Servo Motor on it.

YPVS gives the mid range torque you need out of it

Some little bits.

Removing material to clear the flanged nut I'm using off the fork leg for the correct position. Renewed this bit a while ago, the YZF carrier is not the best idea.

Finished setup for now, Lathed up 16mm Brass spacers and fitted together with 10.4 HT bolts.

98' YZ 250 1/4 throttle with billet alloy throttle tube, is plush like em snappy

New ceramic resistor.

Trying to keep Jap with a Denso W27ES-U plug. £1.70!

Call me the 'Artful bodger' Ran into some issues just using a capacitor to run the Ignitech. So strapped in ol' faithful in what's left of the only space available on the bike.

Slowly rebuilding my TM32. Sanded, wet sanded and polished internals.

Satisfied like glass. Giving a helping hand to the inevitable ingress of dirt to be combusted.

Remounting the WR rad, cutting the thermostat housing down, deleting the oil tank cap fixture from the support and shortening the rear radiator outlet futher to clear the tank. Then moving the whole thing forward to sit flush and safe.

Having alot of fun tearing it about, led me to ignore a serious issue. After letting the chain eat my original WR200 chain guide and very good condition Delta-box swinger, it was time to go back and fit plan A.

Drilled and M6 taped new mounts. Didn't feel like sacrilege after fucking it over already.

I wanted to do this for ages, fitting a YZ/WR 98'-02' chain guide looked to fit in my head. Can now replace it without having to take the swinger off, and readily available to replace now, as WR200 and early YZ 1990-94' sliders are rare, or silly money new.

Ugraded to RFX slider in blue, made from a hard polypropylene instead of silicone rubber. Should do the trick.

Running the airbox door removed and older 3MB airbox tract now with a 450 Main jet can you believe. It's now absolutely perfect with peak power dropping away at about 10,900rpm. She sings. Ready for my new ported top end. Looking to go full road racer at 12,600rpm with the larger carb.

Shortened the chain, back on a Steel sprocket with a 45T 520, good for 80 again which was missed,

I always preferred the original clutch cases, got a nice oil pump housing design. Had to use my 4DL one.

Standard (left) vs EBC's heavy duty clutch spring. Good upgrade, firm clutch with a quicker release.

New EBC clutch plates a while back had trashed my gearbox oil, found this, cause race bike..

Threaded insert and bolt for oil pump delete, re-sharpened foot pegs and brake pedal from the trail bike days.

Prototype V4, 3D printed in a TPU at 80A Shore Hardness like the original. This is chemical and UV resistant filament and it's rather tough!

This is the final design for use with a pressure mold.

Concessions need to be made for 3D printing rubber unfortunately, so now I'm using M5 Socket cap bolts and the original flange that's molded in the Airbox as a sealing face, it actually works out to be the most effective alternative. Much like a YZ Airbox will use the same design.

The Airbox is so important when jetting a 2stroke road bike, we need to control the flow of air and have a place to store some also! Induction theory carries on. The area inside is free of interruption and the boot helps to increase the velocity upon entering the carb. I'm hoping to gain more torque down low by using that stock Airbox volume.

The design now minimises any angles greater than 55deg, this means material does not have to be supported as we print. As you can see, this is the optimal version as the rest of the print can completed cleanly as a vertical slice.

Job done,

So much more flexibility with jetting. Measure 69 times, draw it once.

Mikuni TM34ss finally finished.

*Nobody

ME:

*A custom inlet tract for a DT125R.

Couple beers and some eyeballing and you can make whatever you want.

Getting to old for Pod filters and hacking shit bits together. So if you could, why not re-design OEM equipment in your favour?
Knocked these up on Solidworks to be a straight swap into the frame and Airbox.

The brief, for my application, getting an inlet tract as straight as possible for 34mm or larger Carburettor to fit around my YZ490 shock, which is way larger than the original DTR unit.

Science bitch.

I have access to a 3D printer, so I've been designing and making prototypes just for a bit of fun after work,

Technology these days....,

Had to get out the shed today,

Rebuilt my 3RM02' - TM28SS, polished internals and re-jetted with the Ignitech ignition.

Fitting a Modified 1991'-93' KX125 throttle cable.

She's no looker, the body needs to be blasted, but inside she is minty.

Had a play and uploaded a new Ignition Map and it works well, Noticeable increase in torque low down and a big! improvement between 6-10k. + the 13t/51 setup keeps the power in. I'm having more fun squirting out of corners and sliding the back around in the revs. I don't think shes good for more than 70 flat out, it gets there quicker and that is the fun bit on any bike for me.

Mugged off a bandit 600 in a little uphill race, the dude was definitely surprised. I HATE the Suzuki Bandit. Just do.

Excellent upgrade. I like that the unit was labeled for me.

WR setup on the rear is definitely more rigid and thus more responsive, the back comes out progressively with a lower ride height, and the steering is slower upfront of course, Raising the rear another 1.5 cm should make this a little ninja!

The rear is a new bike, the YZ damper is so nice on Cotswold roads, if you can call them roads, A shock rebuild one day, but it's all just right as is.

So, now the Front end feels rubbish, A YZ Nissin caliper, TDR 320mm Disc and YZ125 - 3JD Fork legs on the shopping list.

Current Jetting:

280 Main
35 Pilot
Needle 5J25 - 5th grove from top.
6mm Reed Block spacer
Pipe Cross Airfilter
Drilled Airbox/w Snorkel in.

3MB00 Barrel - 3BN Cylinder head - Standard Bore.

It's nippy, but would be destroyed by an RS/MX/SX Rotax.

Good old facebook marketplace and £500 cash. That was our challenge, me and a mate seeing how much motorcycle we could fit in the back of an old Hilux.

Unfortunately it was the Works Christmas party the night before I went to pick this up. So I took my chances by taking the only available car, the Fiat Panda and some tools with me.

It was nice of the seller to leave half a tank of old Petrol in the tank aswell. High as fuck on petrol fumes on the way home, I decided I got a cracking deal on it.

How can you not love pitbikes? Poor build quality, awkward to work on, typically poorly serviced and maintained, poor part design and silly gearing.

For £500, it's well used, but the engine was a peach so provided you have the patience these things can be fixed.

The Suspension was awful, had about an inch of free play in the swingarm and the Forks had no damping left. To start with, I had to get into the forks by creating a tool to undo the caps. You cannot buy this item anywhere!

New Seals, and new Fork oil to suit my weight and riding style and it's transformed. The inner seals are blind, so you will need a sharp puller tool to get them out especially as the fork tubes themselves were slightly different internal diameter! Well done Chinese engineer.

Fixing the play. The shock bushes and seats were very worn. And you guess it. You cannot purchase any replacement bush, a completely unique item. Nothing is designed to be fixed here!

So rather than engineer the solution and hit the Lathe with some custom oversized bushes, I wrapped the old ones in some Bronze Paper to pack them out and the pressed them in. Bodge of the Year. Works a treat. And that fix was free.

A Mate bought his a day after, and similar issues to mine all rebuilt by us. This is the first time I could not get a carburettor to run properly, it was Mikuni Copy 26mm piece if shit that would not cooperate. Pitbike 1-0. In the bin.

So I've done the unthinkable and bought a Chinese carburettor...., NIBBI N26mm Race Carb. Yikes.

It's actually pretty good, the overflow circuit is only routed to one side which is irritating and I had to up the jetting considerably from factory settings. But I'm happy with it, Comes with a handy jetting guide for the novice which is decent for Kyle's.

Yes it's cheap....,

Pit bike throttle cables are the wrong thread size, so I couldn't just put on my old KX or YZ throttle housings. So I bought 3 piece CNC thing, apparently these are popular but my god what a terrible design. It does work though.

And Anodising makes you faster.

Someone put a Hydraulic clutch master on this at some time. It works, and that is all I can say about it as it's a heavier pull than the standard cable action...

After replacing all the odd bolts, bolt to long with 6 washers on. The Hex cap next to the Cross pan screw, the missing bolts... Undoing much of the previous 'servicing' by previous owners,

A bit of TLC and a good service, it's a fun little toy making a decent bit of torque with short gearing and enough suspension travel to ride it flat out along the trails. Certainly better than I remember pitbikes being.

Anything you can stick in the back of a 4X4 and be a hero is good with me.

Something different;

Me and a friend organised and got funding for a road trip of a lifetime, starting Cape Town (South Africa), climbing Mt Kilimanjaro in (Tanzania) and then flying home from Mombasa (Kenya). 60 Days in Africa.

The aim, to raise money for The Grand Appeal Charity which help Bristol Children's Hospital.

We called ourselves 'The Rough Riders' and this is our trip, organised by ourselves and sponsored by local Gloucestershire companies and even some backing from Haynes Motor Manuals!

We prepared and imported our own vehicle, a 2005 Mitsubishi Shogun Sport 2.5TD from the UK, and ended up driving for 40 days and covered nearly 4500 miles.

Lots of things went wrong, some butt clenching moments driving as African standard of driving seems to degrade the further north you head.

But we managed to make it home safely. And we are completely broke, but it was worth it.

Rear storage unit I designed in Solidworks, was a bastard to build into the rear.

Our Oil cooler, rear brake line, head gasket and powersteering all ended up failing on us throughout the trip. But we bodged what we could and made do. The mighty shogun limped us home.

And off she went back to the UK.

It was a blast, cheap living, Diesel, and hospitality. It was a hell of a journey, and Africa is a special continent. Not very scary really.

Safe to say, it's nice to be back in rainy UK. And the next project awaits..,

It was our own Top Gear adventure, read up and give us a follow on Facebook : https://www.facebook.com/theroughriderproject/

I bought this edition ages ago. Interesting read. Also proof of concept for Ignition tuning on these bikes, I highly recommend it to anyone.

From Germany... on to the 1997' 125R. Love that riding gear.

Then came 1998. The last year to use the original Oil pump design. The last of the real DT125Rs. You could still get 11,500 RPMs when you wanted it.

This is the end of the DT125R, 99-03' models are completely sanitised and the heavier Generator design that followed make these engines even more soulless.

So quite enthusiastic I own a 2001...

Oh well.

If your are looking for the most refined 125 2stroke ever made, it would be 3RME DT125R.

I found quite a rare copy for the 2005 DTRE 'Stefan Everts Edition'.

No love for the DTRE at this point, fatter and confusing ergonomics, It's amazing Yamaha stretched the DT125R from 1988 to 2007. The everyday 2stroke market was finally dead.

Production of the DTRE completely moved into Europe to.

The RE borrwed dimensions and design from the 1997' DT230 Lanza, Yamaha's last attempt to keep selling a 2stroke relic at that point.

No offence to you DTRE owners. Be assured!

To a great bike, that is actually best when you leave it alone and original..

I'll just leave this here.

@CYBER-NINJA It's werid people say this, A boost bottle and the YIES chamber design from Yamaha never increased horsepower.

All Boost bottles or 'resonance chambers' do is help to smooth out 2stroke induction, which is of most benefit at lower air speeds... Low to Mid RPM running.

@jgr72 The WR200 inlet wont raise the height of the carburettor, but, it will make it clear the Clutch arm and give better clearance around the Shock Absorber.

Also for the love of GOD, do not chop this bike around anymore!!!

I would get rid of my DTR for your 'Endurance Blue' 3DB1 DT125R. They are one of the most desirable models.

See my build thread for carb placement, and note that there is no clean way to upsize carburettor bodies!

EXCEPT. using a (TM30ss) That will just about fit in with the original 125R inlet tract.

https://dt125r.co.uk/topic/77/yamaha-dt125r-01-running-project/73

32 degrees, sticky rubber, cotswold country lanes, 2strokes and considerable beer intake on par with University life.

I ride this thing 22 miles a day as a daily to go work, built this thing to be used and I just 'turn it up' a little on the Laptop for a blitz on the weekend somewhere.

Drawing this project to a close, and enjoying the result, or atleast this iteration of it so far...

I had some clearance issues with the Powervalve under expansion. I removed material in increments by machine sanding.

Custom bracket for the FMF Powercore1 can. Fits on a DTR well.

Built the headlight brackets,

WR400 Face swap.

There is no room left on this bike. Made a mount for the Ignitech Ignition, secure, doesn't suffer from heat exposure and most importantly it's accessible.

As for cooling, air flow is fine still.

Modified AS3 Silicone WR200 radiator hose's to suit this mongrel application.

This leads me to something interesting I found,

I needed a new WR200 coolant pipe, turns out later 4BF4 1995' WR200s use a larger 18mm bore coolant pipe.

I got one brand new old stock from Japan. I've rust protected it, primer and a Gold top coat for a little bling.

Then of course a 4BF4 Waterpump cover is required.

4BF4' Pictured above vs 125R/200R

I never knew Yamaha updated the cooling for the WR200, so I had help getting a used one.

IT ONLY JUST FITS... Tight bruuuh. I made a brace for the coolant down pipe as it's just a braised joint and I managed to split my last one like a clot.

Originally this mounts onto the WR200 Cylinder, so ideally this has to be done to the 125R barrel.

Cooling is now more than adequate,

WR200 Inlet, TM32 fitted. This inlet gives you more angle to use larger carburettor bodies.

WR200 vs DT125R. Inlet tract a little longer, Mounting points have to be modified and crankcase stuffers removed.

New YZ braided brake lines and removable exhaust joint to get the FMF onto the DEP.

(An oldschool mechanical display setup. Dorky but I love this older stuff.

The fun bits. Built to be ridden alot!

Using a base map close to a TZR125 4DL SP, It runs particularly well under 6K.

This DT now shifts.. I use a 4DL servo setting which utilises the PV opening later than the DT or TDR 3SH.

It's far from perfect, but a safe base tune to run on as this is my daily as the weather is so good.

It's run in properly now, and it is glorious. It sounds fantastic over 10,000rpm.

Powerband is up at 9,500rpm and it pulls hard to 13,000.

DTR Gear ratios are perfect for this TZR head and it's acceleration characteristic is spot on, 0-62 less than 6 seconds.

More to come, more bits from Japan to arrive and then finally a Dyno session with a TM34ss fitted.

Stay safe!

(6mm Stainless Steel - Brass 13-14mm spacers)

I made DXF files for Waterjet cutting - for a Stainless Calliper adapter and spacers for a SM conversion using the 'YZF125' Brembo calliper.

If there are a few members here looking to do SM conversions, I could get a few kits together with bolts,

Just a limited run as I have the time for the moment.

Have not touched this in months...
Got it Powder Coated back in January, glad it's done,

Cleaned up all the threads, very satisfying.

Pro Taper - Henry Reed bend. NOT Kevin Windham's - much to my disgust.

It's a shame it had to come apart.

The sooner it goes back together, the sooner it can be destroyed, that is what it's all about.

It just doesn't fit anymore, and fried the wadding in 3 weeks.

RIP. DEP system.

The worst thing is having a Taxed and Insured Motorcycle that looks like this. Chassis needs work.

I can also illustrate the knarly fucking dent to the frame rail I found a few years ago.

WTF... How do you even?

That impact has twisted the down tube, its almost imperceptible, but the engine mounts tell me it's all been effected. I have seen worse before though, much worse! So still a really good base to build on.

Off comes the old barrel, honing marks are still there.

It ran perfect all of it's life. I ruined the mixture towards the end. The Powervalve was completely coked up. If you maintain these things they will see 14,000 miles on a set of rings.

It did heat seize once, didn't last long and never had any-more trouble.

Found an unused WR400 headlight. What a score. Always fancied one.

Single bulb Enduro unit, so nothing special really.

WR vs RX, Not sure what I like more.

I found a good solution, 1987 YZ125 airboot.

Ready for a 34mm housing, so no more pod-filters, which are rubbish.

Ducati Brembo 4 pot caliper and Radial Master cylinder. Using a XT660X 320mm brake disc of my DTX hub, I will be able to sling the 4pot in there.

KPmotosolutions did a nice job. Ported, Port timings revised, Squish revised, crown re-machined, and powervalve revised. Tis a little beast.

All out for top end, It's a 134cc race tuned still to run on regular 97 octane. The Squish height is at 0.6mm. It's pretty extreme. I'm running a Wossner piston kit for some protection over detonation, Still good for a pounding, I except to blow it up.

The old Mitaka had created some damage before hand,

Mitaka vs Wossner. The quality of these forged pistons is really very good.

Shes going to run pretty good. I challenge a 170 kit to outperform this.

PowerValve clean up and modified with exhaust port.

Both a TZR125RR 4DL 3MB-P-00s, but one is a later Y-2 version with a Non Stamped head, which suggests it came of Belgarda TDR. It's a good baseline.

I've done a rough sketch of the port timings between the standard barrel and the reworked one.

I had the Top end blasted, and what a difference, worth doing for the money. Now I need an exhaust...

Yamaha DT230 Lanza - Air Duct (4TP-14437-00)

Came all the way from Japan.

Keeping a controlled Air flow. Jetted, It works well with the 125R, highly recommended. All 170cc Kits should come with a larger duct.

Non existent Mikuni gaskets for TM32-34. So I made my own body gaskets.

Built a TM34 aswell to try in the future.

Full rebuild. A TM32 and 34 have the same bodys so I can tune with both without another custom inlet for now.

hmmm. Got one of my 3MB-P-00 barrels transfers cleaned and Ports re-worked and polished.

Off to get it Ported to a Top end tune, and having my 4DL P' cylinder head and Powervalve fettled with it.

Full chassis rebuild and paint, so maybe by next Summer, she's done. Maybe...

Global pandemic huh? returns to shed

Not been doing alot, just wanted to share some bits.

After 4 years, finally built a proper DTX Brembo Caliper conversion. Threw some Titanium bolts on for some weight saving, and bling.

Custom Bracket and Spacers made, was fun on the old Myford Lathe. Got to force yourself to work in Imperial though...,

Plenty of braking power with Ceramic Pads on a 298mm Disc. To manage the DTR Fork, I've rebuilt them with 15W Oil and 35mm Spring Top Hat spacers, this effectively shortens the spring travel and keeps the spring in its stiffest part of the stroke. It works well enough for me at 70kg.

Could be better, but you can pedal this thing hard into mid corner so it feels pretty sorted for road use.

I've got a USD setup in bits currently, got a set off NOS 1996 YZ250 Forks, if anything, they just look sick.

I will do a Build thread on installing USD forks for the DTR, as I think many people want to do it but are not sure about the parts needed to do so.

Re-mounted my Ignitech CDI with rubber mounts and polished up my bracket, sadly it seems the company has disappeared. I've never had a problem with my unit and this Programmable CDI is the best thing I ever bought for this project.

The spark on this thing is ridiculously good.

I couldn't be bothered to fix my ported 3MB 'P' 134cc Cylinder so i went back to my old 14,000 Mile standard bore 3MB
Cylinder with a TDR unrestricted Head, and it has been so much fun to ride. Just a torqueey reliable DT engine like I remember it when I was 17.

QUICK ENOUGH LOL

Been running different carbs for a few years now, and I have to say you couldnt do much better than well Setup Mikuni TM28ss and the 30ss from a WR200 is brilliant for the 125R.., depending on how good you can setup the floats and mixture.

This is the problem with any carburettor using the standard Inlet,

MIKUNI TM28SS - TM30SS - TM32 - TM34SS - KEIHIN PWK36

My favourite so far has been setting up a Mikuni TM34SS from a Aprilia RS250 and Later model RGV250s, (Same engine)

Mainly, the Venturi is angled so the Fuel Bowl remains level. But it has a really effective power jet and has been easy to setup, it works really well with just 125cc, this engine barks and pulls great at Mid-Range too. For me, I pretty happy keeping this engine under 140cc. It's plenty fun.

I'm using a Modified WR200 Inlet with Boyseen DT200R Reeds. Runs good.

I have a 3D printed Airbox to Carb boot I designed, so it's water tight and easier to jet than a Pod Filter.

Currently waiting to print a new filament that has the right Shore Hardness to produce a rubber part like the original. You need a good amount of flex to seat the airbox and carb together.

This has all been paired with old Nikkon Race exhaust, Handmade, Gas welded steel. There is pretty much no info on these.

I bought this from a guy who used it a couple of times and then stored it for 10 years, as far as I know this is the only DT125R Nikkon pipe left in existence. Which is a shame, because this pipe is so much better than the DEP on the road.

I'm going to copy this pipe into Stainless steel and just keep it the way it is because it suites my application so well. Very large expansion pipe aswell, the design is unique.

Will go further into the restoration of it as it's currently covered in BBQ Black paint.

Long term project aye, I've already had my fun.

I run a YZ 250 throttle with a billet alloy throttle tube, so much nicer...

Recomended.

@claws

Not to sound boring, but, Keihin PWK 36mm of a KDX220

Been there done that, mental, makes no sense. Actually slower overall..

A 32mm can be spot on, if you like to 'hoon' constantly, but these engines are fussy to jet on a bigger carb, I don't recommend it.