DT125R FORUM

@HOTSHOT III
I found that the problem is delivery time when getting them directly, last time I asked it was months.. They are very good to deal with, and they were also willing to do a special version where the map-switch would change both ignition and power valve maps. I don't get why they have two PV maps, but only one is in use. I think both maps should be toggled when you 'flip the switch'. That would give two totally different engine characters with the map switch.

@eriondt125r
You can actually buy any PCDI-10VT and fit it on a DT, but it just takes more effort The CDI is the same, but connectors differ.
A 3-wire servo can be gutted and converted to 5-wire. There are also 5-wire chinese 'replica' servo's sold on aliexpress, but they are also a bit expensive (just under 100EUR form memory). I use gutted RC-servo's on two bikes with Zeel, and that works too. Basically it just needs two wires for the motor and three for the pot.
I use the RD350 Zeel on one bike (and a friend uses one too), and I ordered the same this time because it's cheaper However the RD350-version has no connectors, so you have to use some generic connectors and replace the originals on the bike.

Found this when looking for a Zeel:
https://www.motoracingshop.com/en/unit-zeeltronic-pcdi-10vt-dt125re-x-de06-con-programmable-ignition-power-valve-controller-for-dt125x-re-de06-with-plug-and-play-connector.html

Check ebay etc for used Zeeltronic maybe, but new that is about the price you have to pay.
Adding base gaskets will increase your port timings, maybe not a bad thing though, but an extra base gasket is a significant change on transfer duration.
You can weld and machine the 3BN head or get another one, but you will probably have to machine the other head too, to get a decent squish.
I have the Athena pipe, and it's better than the original (especially if the original is restricted), but also louder.

I would re-machine the head first to a 'proper shape' and squish, possibly raising compresson a little. Depending on what shape the head has now, it can make a significant improvement.
Change the pipe and re-jet to suit the pipe and modified head.
You can also play with ignition timing with the stock CDI with offset keys, or possibly by filing the holes a bit to rotate the stator plate. Easy to get too much advance with the offset key I suspect, but I have seen dyno charts of it giving good results.

The reed will probably not make any significant difference with a near stock setup, you could cut some reed petals from some 0.3mm carbon reed material (I use Polini). Leave the reed stops in in this case. 0.3mm should be ok for the revs you are likely to acheive, and should improve bottom end and throttle response a tiny bit. Going too thick will give you less midrange and throttle response and more pressure drop over the reed (bad -less power).

I do like the Zeeltronic, but you need to be a bit of a nerd to fiddle around to get the tuning right, and it should be done on a dyno. 'Butt-dyno' works pretty well once you learn, at least for power valve to pipe adaptation, but the fine tuning of the ignition is better done on a dyno to make it good AND safe. In the end you will be rewarded with better power (and wider/smoother power band) and better throttle response.

I suspect the head or top of cylinder is not flat if you're having issues again and again. I would take cylinder and head to a machine shop or do it yourself if you have the equipment.

I dab on a very thin layer, and it has always sealed well. I put so little that there is almost nothing protruding after putting the halves together. I use the grey Athena sealant.

I usually aim för 0,7-0,8mm squish for these engines, I think that would be good for the 3mb head too. You could also use a Athena cylinder head (they have inserts), I've seen those sold separately somewhere before. Check that the profile of the piston dome matches the profile of the squish area in the head.

I mean if you did not plug the hole.
If you remove it and just plug the hole, it should not affect full throttle at all.

Sounds like you disconnected the boost bottle on the intake? (YEIS i think Yamaha calls it)
Did you plug the hole? If so, it should not idle, but would run significantly leaner on WOT, giving more rpm if it was rich before.

For you guys in the UK: https://www.gpxmotouk.com/shop-gpx.html
They have the parts to convert the DTR to 230cc, can probably get the complete engine too. If I was thinking of a engine rebuild and/or Athena 170, I would go for this instead, based on what I learned from the Athena 170 kit.

I ended up buying a second DT, this time a tired LC Mk1, but not as easy to find parts as with the DTR in Europe (UK has some, and gets expensive with customs). Hoping for suggestions..?

I don't have the possibility to measure, but the diameter of the 170 pin is the same as stock, but it's longer. It's also lightened with a conical bore, so thinner walls towards the ends. I would not recommend a stock needle bearing with the 170-kit, there will be too much axial play on the bearing, so it can wander out of position. I had a lot of trouble finding a suitable needle bearing for mine.

I think 174 sounds very low. I have measured 190-200 on 125 & 170 Athena cylinders, depending on base gaskets etc. From memory my standard 3MB cylinder is similar in exhaust port height.
Exhaust temp is medium temp in the pipe I guess? Measured close to the exhaust port (but not too close) I bet it will be over 600.
I think you could make a pretty peaky pipe (large diameter, and relatively steep cone angles) to gain power witout losing to much of the power band since it has the exhaust valve. However, I think you need to be able to tune the exhaust valve (Zeeltronic) to the new pipe, especially if it deviates significantly from the original pipe. Maybe take a look at the TZR exhaust dimensions for inspiration?

The spacer I used was just a 1,5mm thick alu sheet that I cut to the shape of a base gasket. Remember the head has to be 'moved down' too, to keep the squish nice and tight. Can be done by machining the top of the cylinder down, or machining the head.
IMHO the head volume is too low from factory, and combustion chamber needs to be enlarged to have a safe CR if squish is below 1mm as I want it (0,8mm now). The 125 and 170 inserts seem to be the same from Athena..

No porting done on mine. I think widening the upper part of the exhaust could add some power at higher revs and keep the low band pretty much the same. Pretty easy to do a portmap on paper, but I did not do it before I installed the cylinder. Just measured the port height and calculated the port timings to get a rough idea what height I should try. Raising it the full 3mm to get the 'full opening' of the transfers gives pretty wild port timings, but it would probably work with custom ignition curve and pipe to make it a screamer (power at high revs). Not what I'm after though. Pretty happy with it as it is now.

Some regulators will not work without a healthy battery

Best thing to do would be a leak test sealing up the intake and exhaust, and pressurize it slightly. I usually 'cheat' by removing the carb, and putting in a plug with a tire valve in the intake, and feed it with some pressurized air (not to much pressure, or seals will blow out). Make sure piston is at TDC, or at least high enough to close the transfers. There will be some slight leak through the exhaust, but disregarding that, it should let you verify that the intake side and crank case is sealing. Listen for leaks at crank case sealing surface, flywheel side, and through the gearbox oil filling hole. You can also spray some soap water on the external sealing surfaces and watch for bubbles. A compressor with a variable pressure regulator is ideal, just adjust the pressure regulator to a really low value.

Thank you! Then the newer snorkel will not fit the Keihin..