DT125R FORUM

@HannesDTX Check all the things @calum said, plus are you sure you've done a FULL carb clean? A lot of people just put them in an ultrasonic cleaner for half an hour and expect to bolt them back on. Doing this doesn't sort the blocked emulsion tube which is a leading cause of DTRs refusing to rev out beyond 6000rpm, precisely the symptoms your bike has. Do a full carb clean including the emulsion tube (the brass tube the main jet screws into). A lot of people (including bike shops) miss this and don't realise it comes out because you have to screw the main jet back in without the brass washer and tap it gently to remove it from the carb body. The space between this and the carb body gets blocked with moisture, dirt etc and blocks more and more holes in the tube (which is how the air atomises the fuel) until it just starts fourstroking and won't rev out one day as this controls the mid-throttle fuelling. Just chucking it in an ultrasonic cleaner usually isn’t enough; you have to actually remove everything from the carb body, physically make sure all the jets and air passages are clear, then reassemble. Make sure the air supply to the emulsion tube is clear as well, it's the small brass tube on the right of the carb body just in front of the carb-to-airbox rubber. You should be able to blow through it, but only just.

It sounds to me like the relay. So the starter motor button isn't wired directly to the starter motor as the starter motor requires a lot of current. Instead the wire is connected to the relay and the relay activates the starter. So I'd look in that general vicinity, sounds like it's starting to go faulty, which isn't bad considering it's age and the high amperage that it is subjected to.

These bikes are getting to an age where the clutch cush drive rubbers will start to wear out. It's possible that this is where the rattling is coming from. Whip the clutch cover off and try and rotate the clutch basket by hand. There should be no discernible play in it. These rubbers sit behind the clutch basket [image: PXL_20260527_183632013.jpg] Sandwiched between the primary gear. [image: PXL_20260519_091204926~2.jpg]

@DTGREENLANER Nice job, that looks ace!!

I’m having the same problem, did you manage to find some ?

Update: it now works, adjusted the timing a bit. Helped and do not know why it worked now since ive tried before and upto no progress then. It idles decent but it only runs nice with the choke on. Without choke on it runs like ass. Ive just fixed all the intake manifold gaskets and made it way better so no airleak. Changed the crankshaft seal and that also should be very very minimal. Not sure where else it could leak air

There were chaps on here that used to do something very similar but to the UK. Go down with a van and collect 5 or 6 bikes at a time. Definitely worth while if it means you get the right bike. My Dad imported a Lambretta GP from Brussells a few years ago, was no hassle.

Fair play that's mint.

Hello Welcome to the forum Yes, photo uploading is disabled as I host all of this myself and imagine hosting is expensive. Imgur was the preference, but is now blocked in the UK and therefore cannot be viewed here But yes a build thread would be awesome.

@Calum It has a 24mm round slide carburator to meet the requirements of the a1 lisence in sweden, downtuned to about 15hp, im just wondering if a TM28SS will fit, they are very hard to find.

Hi there, Pretty sure the RPMs as far as the CDI are concerned are determined by the pick-up/magneto. So when you switch the ignition on and off, the powervalve does a cleaning cycle. Once this cycle is complete and the engine is running the valve should return into its closed state. If it is not, then it's possible that the powervalve wires have been inverted and the powervalve hasn't been adjusted properly. I feintly recall this being a common problem back in the day.

@Calum so i got it together it ran well when i started it in the garage but when i went for a ride when riding it doesnt have power and doesnt rev over 7k rpm when in neutral doesnt go over 9k but powervalve is working and no weird noises from the engine im completly clueless

The DTX comes fitted with a 3MB. It's only the very early 89/88 models that came with the 3BN cylinders. Otherwise all years ran the same cylinder. Surprising there isn't more availability given how many of them were made etc

Oh wow, well you'll be pleased to know not much has changed in the last 20 years for two strokes. Port tuning is as it's always been and fuel injection came a few years ago on nothing but the most elite machines. These bikes are a doddle to get running, so throw up any questions you may have and we'll point you in the right direction.

Sorry for late reply Thank you We carefully took it apart and greased it back up and running nice now, the bike is so much more responsive and acceleration is a lot better

Also don't forget to change bulb in light cluster for an led Kind regards

Hi @yennie , That's cool and I am glad you've managed to get something working for your setup. I am working on something similar to just add a slight angle to the inlet manifold so pod filters don't foul the shock absorber.

They say it's mechanical but the description sounds electrical and they're adamant it's not I still maintain it's electrical related, ignition timing, static angle, etc. But I am not familiar with the ignition system they're running and/or how it's been wired together

Where is the Dyno result with power changes?