DT125R FORUM

Oh awesome.

Is it an improvement over the factory headlight?

Well this last month a disgusting amount of money was dropped on parts for this engine.

• Two Keihin PWK 28mm Carbs
• Two Vforce Reed Blocks
• Billet Inlet manifold
• EBC Clutch Kit + Heavy Duty Springs
• 6 TZ750 Genuine Clutch Springs
• Zeeltronic Ignition System
• Billet Kick Starter Lever
• Magura Hydraulic Clutch Lever
• Chariot Performance Billet Clutch Basket
• Wiseco Blaster 200 Piston (573M06800)
• Modified Idle Gear with bearing

These Wiseco pistons replace the stock Athena pistons due to the 115mm long rods I'm running and the +4mm stroked crank shaft. The head still needs to be machined to accommodate the longer stroke and the wrist pin on these pistons is different to accommodate the longer rod.

This idle gear is lovely, totally unnecessary but was only £60 but seemingly not available to purchase anywhere I looked.

The Magura wasn't cheap, but it's going to be necessary when running all 6 TZ750 clutch springs just to keep the power from slipping the clutch.

(the other two springs are in the post I had to source elsewhere).

Now that I have the basket, I can finally assemble the clutch basket with my straight cut primary gears.

Basket is beautifully made, claimed to be the best on the market and I can see why. It was missing the Belleville washer that sits between the basket and the fastener plate, I bought a genuine basket to chop up and salvage but it wasn't on that basket (apparently they're fitted to 1986 models and later). I managed to find a company that sell them so ordered from them and fitted. Wasn't cheap but I'm glad it's in.

I did replace the steel bolts with some lighter titanium ones (hopefully they withstand the abuse the basket is going to take!)

About 50% of the weight, but hopefully not at the expense of strength!

The washer is installed with the raised edge facing you. The fastener plate will clamp down onto this edge.

Engine is coming together nicely now though.

Well sounds like a fantastic purchase.

I thought I recall the 3SH models being quite sought after and sounds like a good buy for the money. Sadly Imgur is blocked in the UK so I can't see the images right now, I'll have to have a nosey on a VPN.

Yeah, there is an okay aftermarket scene for tuning, anything that'll fit the DTR engine will fit the TDR engine. It's the TZR 125 (2RK???) models that had different engine setups, but the TZR Belgarda shared the same platform as the DTR.

No, the 4DL would have a straight inlet. These don't fit the DTR as thr carb then fouls the shock absorber.

Reposting images as Imgur not longer viable in the UK.

Reposting images as Imgur no longer viable in the UK.

Reposting images as Imgur longer viable in the UK.

Reposting images as Imgur is no longer viable in the UK.

Reposting images as Imgur no longer viable in the UK.

Reposting images as Imgur is no longer viable in the UK.

Reposting images as Imgur is no long viable for the UK.

Still got this though, haven't done anything to it for a very long time.

Have you earthed the green/black wire?

Sounds like a restriction.

Where is this PWK from? Is it a good quality carb?

Although not the source of your problem here, as the demand/load on the engine increases, the reliability of the fueling also becomes more important. What might be fine in lower gears, presents problems further afield.

Removing the Snorkel will adversely affect the performance. Removing the snorkel will result in turbulence adversely affecting performance.

So put the snorkel back in.

You'd be better focusing on getting a DT230 Lanza Snorkel as it's slightly larger flow.

https://www.cmsnl.com/products/duct_4tp1443700/

Or a cheaper easier solution is to 3D print a larger snorkel.

Well, you need to figure out whether this is indeed the problem. Obviously I can't be certain having never seen the bike, you'd need to take some measurements.

You don't need to get a new top end, correcting the squish is standard practice on two strokes.

This is most likely the squish.

If someone built that top end for you, they probably used too thick a base gasket reducing the compression ratio. The cylinder head could sit be marginally higher than what it was before, meaning the squish is off.

I am not saying this definitely the case, but would explain why you'd lose bottom end. I am not sure about the heavier piston, sounds like a cop out, but if a different dome was used, different profile, then same answer. The squish is affected.

A vast majority of power on a two stroke is made in the head, so it could be that the squish band isn't correct. This is a very simple and easy thing to fix and measure. All that is needed is a set of vernier calipers and some 1.2mm thick solder wire, with a dab of grease to stop it falling into the bottom end.

Could be this, especially as you say, it was fine before the top end rebuild, noticeable after.

I once went from the stock 3MB00 cylinder, to the TZR R Belgarda 3MB00P which has a raised exhaust port by 1mm and as a result, greater over-rev (ideal for the TZR) loss of bottom end (less ideal for the DTR).

I went from lifting that front end up with ease (no small feat on my heavier setup) to having to work for it.

Now I run a ported Athena 170cc kit and I love it for the low-rev grunt. I have my RS125 which is lightening fast so I enjoy both aspects now :)

I am by no means an expert and please someone else chime in and correct me, but based on what you've just articulated, this could explain it.

Due to Imgur being blocked in the UK, I've had to rehost these images. Maybe I'll reorganise it at some point, but need to do this for all my projects :(

I'm sure someone here will be able to point you in the right direction.

What we've been seeing in recent times are a lot of DTRs being imported from Europe, these can come with subtle differences, this may be the case here.

This is the 3NC wiring diagram.

I only have a Haynes manual so can't speak for what other diagrams look like.

I have also hosted the workshop manuals here: https://dt125r.co.uk/topic/3258/yamaha-dt125r-200r-workshop-manual
https://training.dt125r.co.uk/files/Yamaha_DT125_Workshop_Manual.pdf

This may be useful.

I'd expect there would be a few issues, the bike wouldn't handle particularly well if the front and rear wheels were misaligned. The bike would have a tendency to crab.

 |     <-- Front wheel
[  ]   <-- Frame
  |    <-- Rear wheel

Figure: Exaggerated misalignment

I'd be inclined to measure/check and if necessary locate and reinstall the speedo drive.

Aww nice! I've just received another Zeel for my RD yesterday. I've got to wire the plugs myself mind you as it's going into a Cagiva Mito.