DT125R FORUM

@eriondt125r Running an engine where only the crankshaft is stock and fitted with 170cc kit also tuned.
The head tuning was done for fuel efficiency then power delivery in mind when gas prices where lower.
Both where achieved at a cost.
10lt (main tank,didn't measure the reserve) for 260kms up to 7k rpm,screaming bike up to 11.5k.
Power/fun yes.
Usability not so much, I have found only 2 gas stations out of 15 with in 20km radius from where I live,that have the appropriate fuel quality and 100 octane gas.

A tuned 3MB head+cylinder is fun and quick. better than a stock 170 kit, overall no.
A very tuned 170 is another level,between a stock 3ET and 3XP,dare to say.

@eriondt125r
Leave the flywheel alone. The TM28 is ok, DT200R uses the same with different jetting,so it's up to the task. Adding a power jet is a bonus if doesn't have integrated.
Squish is ok and already needs minimum 96 octane as Athena mentions.

I tempered with squish,height and combustion dome and now needs minimum 99+ from a good gas station, otherwise pinning heavily. Doesn't worth with gas prices.
I plan to lower the compression and dome shape so be able to run 91 octane gas.

@eriondt125r
The YZ reed cage was used because it suited better my setup.
Dropped my max rpm, widened the power band. It's a more civilized bike now.

An 170kit as is,with a tuned or aftermarket reed valve,an after market exhaust and a programmable CDI (zeeltronic or ignitech) will make a whole new bike and an 70-80% of the second route.

The other route is from ground up build and tune almost everything in the engine and not only.
A lot of reading, searching, calculations, note keeping, machining, adjusting, combining info/parts.
Will give you a bike like what you see from a specific Portugal tuner, but with more money, time and headaches spend in the end.......knowledge is a side-effect bonus.

I will not recommend this torment to you , get the first choice.

The Boyesen dual stage reed bolt on to the dtr reed cage. The stopper is removed and no mod required.

I liked the Boyesen dual stage reeds,the gave me a very angry kick at the powerband.
Switched to a read cage of YZ125 after.
Dep exhaust at 32mm widened at the port.
Port tuning I would say is a must.

Last couple of days I 'm considering to get a Piaggio Vespa for general use and no project bike,just good take care.
But the prices are to the sky high and I don't want a restored, or a trash bike to restore.
Just a good condition runner this category in Greece is non existant.
Only 200cc Cosa's and 50cc/125cc PK's models are relatively cheap because they are not wanted but not well maintained.

Is the power valve correctly aligned,if it has the diamond shaped base?

Hello and welcome bud.
Like Calum said,tell us some more of the DT.

Happy new year to all.

I am collecting photos from small jobs I do on my DTR, will post them when 2025 stops kicking me like 2024 did.

Merry Christmas and a happy new year,wish you good health to all, everything else is obtainable.

@HOTSHOT-III Interesting bike that Aprilia,never seen one before.
A DT could transform into something similar,twin headlights, modified bigger tank, keep it's enduro costume.

@Calum I would grab a tig/mig and extensively repair the frame. But I am known to see hope/light in garbage stuff with a lot of time and work coming back to life.
Example. I was offered an XT500 with low km's but sea salt corrosion damage to the frame,not passing "MOT" here.Very low money,but I have no time....for now waits to the owner garage until I find time.

If the cabling is not messed up the main light runs directly from the stator, doesn't load the battery.

Maybe it's from the 3ET DT200R,has the same carb as the DT125R but uses different numbering in jets, the main is 150 but is not smaller than the 210 of the DT125R.

Motul motocool expert (yellow) and Aisin coolant for motorcycles (blue)
I prefer Motul because it's the best I tried,has the least fluctuations in the temp during usage.A little expensive 10 euros per liter.Normal riding city or cruising 65-75c temp,on the high side 87-90c when going up the mountain through steep bad fire roads.
Second one is the Aisin,similar performance, normal riding city or cruising 65-79c and up to 95c on the fire roads.5L for 21 euros.
All these on Greek hot summer evenings,34-38c.
Currently filled with Aisin because I had 3 liters left and doing some work on the bike.

https://dt125r.activeboard.com/t49963266/cdi-compatability/

It's from the old forum,hope it helps.

@Calum That's another chapter of 2stroke tuning,we talk about a "cough cough" a somewhat civilized power delivery or the 2stroke mad max madness ????
@Sid_Strummer can tell us what he want's

@Calum I know.It's my opinion that if you have to grind the PV you are at the max of what Yamaha designed.
You can overbore to max 70mm I think with the PV at it's limit,no reason for that. 74mm is the outer diameter of the sleeve if memory serves ok.
Resleeve and have all the fan from the start.

@Sid_Strummer I remember that max bore is 68mm, after that you have to grind the PV, I wouldn't do that.
Re-sleeve it to the 66mm.

@SpookDog I always keep old bearings for use at this kind of jobs.

Last time I had the bike working I did about 250km (city/open road mixed) on 100 octane,then switched to reserve.I am running a little high CR,no 95 or 98 gasoline for me.