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Lot's of information on this site already.
I find going to Google and use site:dt125r.co.uk 4bl derestriction better than the internal search.
https://dt125r.co.uk/topic/3102/derestrict-yamaha-dt-125-r-1997/66?page=4
It does depend on what region you live in, but the easiest way to get full power is
Make sure you've got 3MB cylinder head (3BN denotes you've got a combustion ring head that benefits from machining out). But otherwise you'll be laughing!
There are wiring diagrams and manuals around on this site.
Try searching using the built in search.
Another great tip is using Google
In Google search engine do site:dt125r.co.uk wiring diagram 6 wire and let Google indexing do the heavy lifting.
The DEP pipe is tried and tested and I was really impressed with it.
Here in the UK, they typically rust before too long. I always cleaned mine when putting it away and it held up well.
The one in the photo looks similar that it's mild-steel, so you'll want to get that painted before you fit it.
I run a Romeu Henriques pipe on my DTRE. I've had it since 2011 and there isn't a blemish on it as he made mine out of Stainless. It's also not cracked in that time either.
I went for underslung due to my setup, but he does wrap arounds also.
So the mounting points on the frame differ from the DTRE/DTR.
Whilst the engine is basically identical, so the actually performance/shape of the pipe won't be affected by the later design, the frame mounting points are different.
It's worth noting, the very early DTR's ran a 3BN cylinder, so there are subtle differences in actual engine specifications. Can you confirm that you're running a 3BN cylinder? Or the revised 3MB cylinder?
I can't remember whether or not the fact the mounting points differ was a deal breaker or not, or in other words, did it cause it to foul the frame.
My gut instinct is no and you should be okay, if you can make a couple of brackets.
I've done something similar with my Aprilia ETX, where I have put a full arrow system off of the SX models. The engine is the same, but I've had to fabricate up some brackets to get it to fit.
The most easiest carb to get ahold of is probably a Dellorto PHBH 28mm. Found on restricted RS's, they're widely used and reknowned for being easy to jet.
I run a Dellorto VHSA 32mm carb on my DTR.
The reason I've gone with this carb, although rarer and harder to find, is that they were factory fitted to the TZR 125 RR Belgarda which effectively ran a DT125RE engine. Which just gave me nice confidence that it was a solid choice to make.
Another great carb, albeit harder to tune, is the VHST 28mm.
So keeping the size the same as the Mikuni, but this time Flat Slide instead of Round Slide like the PHBH.
Remember, bigger is not always better. Going from 28->32 doesn't necessarily mean more performance. Fair enough if you're giving the engine a tune up, but if your plan is to keep it relatively stock, then sticking to 28mm isn't a bad idea.
Hi there,
I would leave the carb settings alone. DEP themselves don't even recommend changing the settings for their setup.
There can be several factors for poor running, a lot of this is well documented on this forum.
Probably the key one here that I am sure @hotshot-iii would say is the emulsion tube in the carb. Often gets overlooked and clogged.
Cleaning it verbatim won't help, it'll need pressing out and properly cleaning, before reassembly.
Zeeltronic easily the single best upgrade for my DT 
Disc guard looks great.
Yeah sadly these bikes aren't going to pull your arms off or anything. They're pretty decent at what they are though however.
Lovely colour scheme on yours for sure!
Well the best thing to do is to check to ensure that the thermostat is working correctly. You can remove it and place it into a sauce pan and check to see if it correctly opens at the right temperature when left to boil.
If your daily commuting the bike, then leaving the thermostat in is advisable. Yamaha know what they're doing.
If you start tuning the bike and pushing it beyond its original specifications, then you may want to consider removing it.
The thermostat isn't just there to aid heating up of the engine, it also has a role in providing pressure in the cylinder head to avoid pocket stagnation of gases. So it's actually important it's fitted.
I just noted that these engines do run warm and removing the thermostat allowed my bike to run at a more consistent temperature when under load.
DTRs do seem to run very hot in my experience. Always have, wouldn't worry about it.
My Aprilia RS usually sits around the 60 degree mark, I run a Vapor Trail Tech unit on my DTRE and it's ready 110 before!
To combat this, I removed the thermostat and now it sits around the 60-70 mark, just note you do really need to be careful when warming them up to ensure you don't cold-seize the engine.
Yeah okay, well that sounds like you've ruled out all most of the basic things.
I've had this before with a faulty ignition coil. These can still be bought brand new from Yamaha and I highly recommend going for genuine coil over an aftermarket one. The aftermarket one I had led me on a wild goose chase trying to figure out the intermittent fault.
You can measure the coil to see if it's within tolerance, what I was finding was that from cold it would work a treat, but once under load and warmed up, it would fail to fire above 4k RPM.
So it could be a worn out ignition coil, however unlikely that may seem.
Other than the stator/pickup, there really isn't a lot more to these engines to get them running.
The side stand sw and the whole interlock chain should be good. I even bypassed all of that by grounding the blue yellow wire to the CDI directly
If I had to guess, that's probably your issue.
I see this time and time again with the side stand switch. My brother had a similar problem on his 2001 DTR many years ago now. My advice would be, if you're struggling to figure out a problem, get it as close to factory as possible, otherwise you're going to be chasing ghosts.
No a mechanically unhealthy engine wouldn't necessarily affect spark, but given how you described riding the bike and it cutting out, indicates that you had spark.
Okay, well it's good to know it's unlike to be water corrosion 
But still check those connections anyway to make sure they haven't vibrated themselves to pieces.
Ensuring good connection between that block is essential.
As I said previously, triple check the neutral switch, clutch switch as well. If they are vibrating loose they will cause intermittent problems.
Oh that's frustrating.
There really isn't an awful lot to these engines. I've never heard of a stator go bad. I've had a bad ignition coil and I've had an aftermarket (bike sadly got stolen from me) ignition barrel disintegrate and cause this problem.
A common one is the side stand switch, similarly the neutral switch and the DTRE has the clutch switch.
Check the plugs from the ignition barrel to the wiring loom as they can have a tendency to trap water and destroy the connections.
Did you say whether the engine is healthy or not? Is it making a good PSI? Are the intake and exhaust pathways clear?
What specifically do you mean by cut? The Tachometer is mechanically driven on the DTR. So you need to replace the tachmeter cable back into the gearbox and the clocks.
If you mean the lights etc, then there are many wiring diagrams already uploaded to this forum.
Workshop manual is pinned: https://training.dt125r.co.uk/files/Yamaha_DT125_Workshop_Manual.pdf
@hensmaxim Just contact him directly via Facebook or something, he did my pipe for me silly cheap.
Hi there and welcome.
What a great machine, they're becoming rarer and hard to find in unmolested condition, so definitely bear that in mind before tou do anything drastic and keep all the original parts.
I super moto'd my DTRE using Yamaha WR450F Forks and Aprilia RS125 wheels just because.
But the simplest way, to my knowledge, using the stock DT200R would be to grab the DTX setup as that should be a drop in replacement, may need to machine up some rear spacers for the swinging arm, or just grab a DTR rear swinging arm.
If your bike uses the ally arm then it's just easier to get spacers made. PCBWay will make them for £40 no dramas at all.
Sounds great though, I always wanted a DT230 Lanza personally.
I'm not familiar with the market, but a cylinder piston combo with all the work ready to go has got to be £300+. Any more than that then I wouldn't understand why someone wouldn't go for a brand new Athena 125 kit, or a little extra for the 170 kit.
The Zeeltronic, new they're around £240, so with the programmer I'd say £160ish is what I'd pay, otherwise I'd just go new.
Hope that helps.
Oh how annoying! I've seen this before when people have incorrectly set up the YPVS servo and stripped the teeth on the gears.
It's probably easier to just buy another YPVS servo sadly than trying to find the individual cog.
https://www.ebay.co.uk/itm/307114030022?_skw=Yamaha+DT+125+R+YPVS+servo&itmmeta=01M0T0CTAKVKYBVERW4KK9HKJQ&hash=item47816c33c6:g:QqIAAeSwkVdqdvO2&itmprp=enc%3AAQALAAABAGfYFPkwiKCW4ZNSs2u11xDV5F88zNLFmQlOj5cc4%2FxlPVfMrS0CX9zdgmCMx0exrIiMBYEnl2C70gEhZcvwr3BYq%2BewLJHyMjxf%2BATBLTUnAq5B4Os%2FAuVyeOUNpVSRYxblUNuwL%2BjqWn0F95mbpkEWkXEDU%2F4blrRDuajNXDPVd8py1aTbWsSecsyFqwFQqqWjrgMG65s52PTjh2LPZ%2FOmWbQsy4dMVcVkq6VX2lCX6cdUUBN6SMPZHm3xNkDwYsJXuOa1TCyyOEaSwcuLKfJrQwb9YP1PtVMNdQS0UqCxAXfBI4hQNMZjPJwu4V6qdKAjffzCnESPO3DSoS0%2FsfE%3D|tkp%3ABk9SR9als8CGaA
If you have access to the a 3D printer, or are capable on CAD, you might be able to 3D print a new set of teeth, setting the TPU to 100% fill should be strong enough to cope with the demand. My 3D printer is pretty darn accurate so it would probably do a fair go at it to be fair.
