DT125R FORUM

You can take a piece of soldering tin and bend it and stick it through the plug hole to get a rough measurement of the squish. If the solder is not pinched you can 'double twist' it to get a reading. This should give you an idea if it's the cause. A good value should be 1mm or slightly less IMO. You can find different thickness base gaskets in some places, like here: https://www.motorsportgoetz.com/Cylinder-Base-Gasket-03mm-Yamaha-DT-TDR-TZR-125

I'd would just listen to hotshot-iii - https://dt125r.co.uk/topic/3551/do-pipercross-air-filters-really-flow-better-at-all I haven't ran an airbox on my DTR for 10+ years and I just used the stock filter the time I had it. So I don't have any opinion on it.

I would say so. Is quite similar to the factory headlight, but it gives the modern look I was looking for, with a cleaner and whiter light.

Just measure from the inside of the fork leg to the rim on each side, +-2mm should be ok I think. If you release the nuts on the axle clamp on the right side (if I remember correctly) and pump the front suspension up and down, and then re-tighten, it should not bind. If the seals wear out too quickly, I would check the surface of the fork tubes, so they are not damaged (pitted from rust, flaking chrome etc.)

@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.../ [image: 53107628675_b20a021b82_b.jpg]

That's right, I forgot about the clutch switch!

@lucasg.03 Take off the stator cover and see if you can see a dribble of goop coming from the seal behind the flywheel (also possibly a good time to get a flywheel puller if you don't already have one, I think Yambits sell one). Once you take off the flywheel and stator you can replace the seal in situ as long as you're careful not to mark the sealing surface of the crankshaft.

@Calum said: These were almost a nightmare to source 16 years ago, I can't imagine trying to source one now. My bike was stolen in 2010 and they smashed my headlight, the only one I could find at the time at one of the lugs snapped off. Looks like there is one for sale on eBay: https://www.ebay.co.uk/itm/117220896053?_skw=DT125re+headlight&itmmeta=01KTM8B5217RAZTYS7W99928FR&hash=item1b4ae8ed35:g:y7gAAeSwpAdqHbG7&itmprp=enc%3AAQALAAAA0GfYFPkwiKCW4ZNSs2u11xBZmLIU--K9J71U9lN1jJvKGElmcMKBjUzhn5JV3gvFr%2BI2mNwns0SlbUycS%2Bw9y3Qsk%2FC9Cp56dPrHcSEz%2FAr0Zq5el9BEEdpE--23lnRC8fU0%2Fsn13ryM871mf1jmM1dUjkmiSvaLNgJjb67pd3KfdVjuND8nPx720y4ajz9BPqgS8GUW%2FCNLpWF1MTDMkYcIXC7cHLcpOan7woIP1A2k2vjESEOPdlk4W2oy4yUcxyO%2BXWy347GqH%2BHrWnu%2F2Og%3D|tkp%3ABk9SR5bRrIjVZw Looks like there are some copies on eBay as well: https://www.ebay.co.uk/itm/188014865985?_skw=DT125re+headlight&itmmeta=01KTM8B521KCQCFP6HVFB9B97Z&hash=item2bc68f2e41:g:v4oAAeSwOt5pf0Q6&itmprp=enc%3AAQALAAAA8GfYFPkwiKCW4ZNSs2u11xBGAd3jIpQ1I%2FPeoct0WRAbZx%2BSpsbDaUmQIjZgqRPgUJo7nG5bGWKGBRZtJJ4k6kWqRTJdLi2QjCbWA%2FBE6jgcnSjbxqmpxc5alD7AkePHPryhwNx3wJMQx9Nn2c%2FJBb%2FaX0A7Z%2BlEzJ6pVoqrlh3sZUh2UZ%2BqkVZwe2vBfwA2F39HuV9O1D2z%2FSIMHbNWWFAOiiE%2BG%2F8xlRqkrAHFOwt3oKAIwYBpeHVG82hZBHdODyJwGkKG5Ef9gkphJk0fgSnlvoW%2FpV6wkCrHIDEqggbFJ3LfV5W5qwYpTWvJNjb1RA%3D%3D|tkp%3ABk9SR5bRrIjVZw Thanks for helping and sorry to hear about the theft/ damage. I had a different bike stolen around the same time period and wasn’t so fortunate with them burning it 2 doors down in a wheel barrow - I can only assume the chain & locks were giving them trouble. I purchased the unit from the first link as it’s stock and doesn’t look in too bad shape - I’ll hopefully be able to do some sort of refurb with the damaged unit I have right now and keep it as a spare now knowing their scarcity. Thank again! - one step closer to getting her back on the road.

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

..and you need the battery too, not just the regulator. Forgot to write that

Thanks for that I ll go through it at weekend

Clutch can make noises too, for example if the rubbers between the gear and clutch cage have gone bad. Check the play if you remove the cover.

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.

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.

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. [image: 52172141696_84e3b69382_b.jpg] 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.

@Calum maybe i could check the exhaust to be sure indeed, ill try that first. Some time has passed and it suddenly was gone but came back after a short while, very weird haha. The spark plug color is deer brown so a little rich but more for climate purposes because in Belgium the weather is so annoyingly unpredictable. But it would be weird if it was fuel related. Because it drives very well in alle the conditions for the past 300km. A have a bad habit to be a perfectionist so i can break my mind about to find the cause haha.

I can recommend one smelling of strawberries: https://www.ipone.com/en/eshop/product/r2000

If you look at the coolant reservoir at the rear, you will notice that it has a hose going to the frame. I take that to mean that the coolant is routed via the frame tubes. Pipes. There is no hint of an explanation in the workshop manual, though. Perhaps you have a crack in the frame?

Well this last month a disgusting amount of money was dropped on parts for this engine. [image: PXL_20260514_154633826.jpg] 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 [image: PXL_20260519_090422306~2.jpg] [image: PXL_20260519_090204554~2.jpg] 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. [image: PXL_20260512_082334371~2.jpg] This idle gear is lovely, totally unnecessary but was only £60 but seemingly not available to purchase anywhere I looked. [image: IMG-20260507-WA0005.jpeg] 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. [image: PXL_20260530_084354385.jpg] (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. [image: PXL_20260519_091147857~2.jpg] 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. [image: PXL_20260519_091204926~2.jpg] [image: PXL_20260527_182919884.jpg] I did replace the steel bolts with some lighter titanium ones (hopefully they withstand the abuse the basket is going to take!) [image: 20260522_143841-COLLAGE.jpg] About 50% of the weight, but hopefully not at the expense of strength! [image: PXL_20260527_183632013.jpg] The washer is installed with the raised edge facing you. The fastener plate will clamp down onto this edge. [image: PXL_20260527_183640084.jpg] [image: IMG-20260530-WA0000~2.jpeg] Engine is coming together nicely now though.