DT125R FORUM

A prime candidate for this could be:

• Worn Friction Plates
  • I've not seen this personally
• Worn Steel Plates
  • I've not seen this personally
• Incorrect Torque Settings to Clutch Springs
  • Worn Clutch Springs
• Incorrect Gearbox Oil
  • I have had this personally.
• Incorrect Assembly of Friction Plates
  • The smallest friction plate should be installed first, the rest in any order.

You just want to use 10W-40 Semi-Synthetic Engine Oil, avoid Castrol Magnetec as I had clutch slipping issues using that type of oil.

If you've addressed the above issues and are still having problems then given the cheapness of a clutch rebuild kit I'd just grab EBC Dirt Bike clutch plates and new uprated springs and throw it back together.

@Stensar Doubtful as he hasn't been online for 6 years.

Thanks for bumping this though....hhhmm potential purchase.

@dave1w need to hear about this...

@HOTSHOT-III Glad to hear it, your help is invaluable.

Happy New Year

Hope every made the most of 2024 and it's now onwards and upwards for 2025!

Thanks to the contributers over the last 12 months helping those with questions.

I look forward to seeing what 2025 brings us in terms of projects. Although the forum is very quiet, I plan on making a few posts on the DTR related projects I've been working on.

@FloWolF
See below threads which have said:

Its strange but cables going 1 - 2 , 2 -1 .

https://dt125r.co.uk/topic/2893/power-valve/2

https://dt125r.co.uk/topic/757/cleaning-cycle-on-dt125r/3

The right hand side houses the screw that threads the two halves together. There is nothing surprising about that.

Take care when removing as the screw holes can become brittle and are prone to cracking, so just gently pry the sides open.

I mean, two stroke to lubricate in the loosest possible sense. Unburnt two stroke is quite sticky, hence why the powervalve needs cleaning to ungum it up.

Splitting the powervalves can be a little frustrating in order to properly clean the system out.

@FloWolF I have validated your email now.

@FloWolF Yeah I haven't implemented email verification. I probably should though, I get a lot of spam.

@ALLE19E04 Hello there and welcome.

That is the Yamaha Energy Induction System (YEIS).

You should also find another one on the carburetor to airbox boot.

On June 30, 1980, Yamaha announced two new energy-saving engine system technologies that it had developed independently: the Yamaha Induction Control System (YICS), a technology for 4-stroke engines, and the Yamaha Energy Induction System (YEIS) for 2-stroke engines.
YICS reduced the amount of fuel consumed by speeding up intake charge to the cylinders, reducing combustion time, and increasing combustion efficiency. This technology made it possible to create energy-efficient, low-cost engines.
the speed of intake charge in the intake manifold to ensure stable intake efficiency, which results in improved output and lower fuel consumption. In testing on actual motorcycles, it was confirmed that fuel was conserved by around 10%. Development focused on 2-stroke engines, but the technology could also be applied to 4-stroke engines. YEIS was first used on the YZ motorcycle in 1980, then on four 2-stroke models in 1981.

The Yamaha DT125LC had these:

Just push the piston back into the caliper. Make sure you undo the reservoir first however.

I don't think there is anything special about the way the front brake pads go in though. It's been 10+ years since I've remotely looked at a DTR caliper but most calipers are fairly self explanatory.

Wow another year has really flown by, so I just want to wish everyone a wonderful Christmas and here is onto another year of DTR adventures together.

Calum

@mbmO8 Not according to the parts diagram.

https://www.fowlersparts.co.uk/parts/4159461/dt125r-3rme-1999-060-a/front-wheel

No loose wires between the ignition source.

From the real brief description you've provided, if the engine is healthy, fueling is good and the airwaves are clear, then it sounds like an ignition problem to me.

I have seen before where the exhaust pipe was full of water and the bike would really struggle. That was an odd one as I never thought about checking the expansion chamber.

This improved when I restricted the air flow, the bike behaved, but I left help before the problem with the exhaust was found.

I mean, like I said, I'd just bin the powervalve off for the moment and run the bike pinned, just to eliminate it as a source of problems.

I'd check the ignition side of things. You running a genuine 3RM coil? I bought a "Racing Coil" once and it took me ages to figure out that this was the source of all my running issues.

I'd start by just pinning the valve and disconnecting it to just eliminate this as a source of problems.

Sounds like a short to me but haven't got a lot to go on.

I'd do a compression check and get an idea of the state of the health of the engine before diving in too deep.

Obviously your description is rather vague so it could literally be anything.

Do a compression check, this is invaluable and will give us a good insight into the bike before checking things.

Basic stuff will be:

• Head Gasket
• Spark Plug
• Fuel/Air
• Exhaust
• Electrics

Would be how I'd approach this.

I've had similar problems myself with regards to an aftermarket ignition barrel that disintegrated on me and was causing gremlins.

@HOTSHOT-III I was waiting to get home to grab my Haynes, so thanks for chiming in.

The Mikuni TMX28 is a very good carburetor, I wouldn't swap it for an inferior Chinese part. You'll risk an assortment of fueling issues which can lead to detonation and engine destruction.

Carbon fibre reeds are your cheapest option for a "Performance" upgrade. I didn't notice any difference with them but that's your entry level upgrade. The Zeeltronic is plug and play and comes with several maps to choose from. As I say, single biggest upgrade from me, but the UK ignition system was restricted and I don't know about any other regions.