DT125R FORUM

I never could get my DTR to run on those shite orange coils.

https://www.cmsnl.com/yamaha-dt125r-1999-3rmd-germany-293rm332ga_model39887/ignition-coil-assy_3rw8231010/

There is a genuine coil brand new stock there.

I found that the bike would idle but refuse to rev and cut out. Rode it back from Wales like this back to Cheltenham, couldn't rev past 4k, was a nightmare.

So lesson learned on that one sadly. My brother had EXACTLY the same problem with these type of coils on his RD350. So it could be something as simple as that.

Make sure you've got good earths to the frame as well. Has the frame been powdercoated recently or anylike that?

Probably worth mentioning, as you can see in the background of this photo, I have managed to acquire a fully supermoto setup for this machine as well.

These come off the Aprilia MX 125. Since I'm running an MX rear end, that should be simple enough to swap out, but the front end shows some challenges.

The MX125 front wheel uses a digital speedometer, so swapping out the front end means losing the speedo.

Instead, I managed to find a brand new old stock MX front rim, and I've also managed to source an RX125 front hub, so I will look to lace the RX hub onto the MX rim, thus retaining the original speedometer configuration. The rear wheel is in poor condition, the hub has snapped in several places, but I managed to find a brand new old stock MX rear hub, so the plan is to lace both wheels and have an easy to swap out setup for both road and trail riding.

Slow slow progress on this...

It's really not far off completion, I have been addressing the wiring harness as it was completely torn to shreds. It's all starting to come together now and it's good to see the lights come on after it being sat in the dark for 4ish years.

I really feel as though it's getting close to rideable.

There have been a lot of problems with pretty much every component, but brakes are now bled, radiators are plumbed in and it's almost ready for some fuel and it's first start.

I mean....

As I say, I can't see how this doesn't affect performance!

Only use genuine coils. The cheap orange ones simply don't work so make sure it's a genuine one.

@Yaya97422 Vert/noir

From my experience, the catalytic converter was so restrictive that I cannot fathom how it possible could not have an adverse effect.

I do think, leaving your pipe standard is really ideal, especially as these bikes are appreciating classics. Instead, just grab yourself a DEP pipe and be done with it, the weight saving alone is worth it!

Do you have a powervalve fitted or is it fixed?

It's in my experience that my DTR never started without choke, so that's normal. It needs to get to temperature and then you can remove the choke.

Sounds like you need to strip and clean your carburetor, based off what you've just said.

It could be float level height if it's just shutting the fuel off before it's even getting a chance to get into the bowl.

Strip the carb, removing the atomiser and properly clean the carburetor in and out, being careful not to damage it as the components are brass and delicate.

The engines are very basic and provided you've got compression, spark and fuel ,it'll run.

If you can confirm that it's got spark and fuel, then check the compression for the engine, should get around 140PSI. Anything below 90 PSI and your engine is going to need an overhaul.

What year and which bottle?

Early models only had the YEIS that goes into the inlet manifold.

Later models had that ones that go into the carb boot.

I don't recall them mounting to the frame however, it's merely attached via the carb inlet and the carb boot.

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

• Zeeltronic Ignition
• DEP Pipe

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.

Float valve height sounds like it needs adjusting.

I can't say I am very familiar with thise pipes sadly.

I have been away from the tuning scene for these bikes for many years now. It's been years since I've even ridden my DT to be fair.

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.

One for sale here: https://www.ebay.co.uk/itm/178501570394?_skw=Dellorto+VHSA+32&itmmeta=01M4B4V0QQEPEYJMTHPDP73MJH&hash=item298f85cf5a:g:QzEAAeSwwDVqqknx&itmprp=enc%3AAQALAAAA8GfYFPkwiKCW4ZNSs2u11xCsZ9R43qCdhmBbcO8vd2J2b6UmsaleZzaYCXtHKDFciw7JJKWAv%2BVU1RMnsTcB6BR1oQISPasgAcqE0jvZsRV6c%2FlVyBaJXcN8rrE44oBe2oSQMMj8qAaObD%2Fbe28WiBSFTDYhptWeveTmzxQZ09RFGD7JnvJgWfjWhS4BRVr1FAcIy%2FVPcCRof3cnpiW1FFNAA8NGpOV3g7ZB2Ofvh56ymFldlS74mqGTajYR3fy53FzAnXiqxtqLCFu%2F4or12IxEXL%2B%2BYXIOMAsOoLkx2wRBM6v%2BZd63q%2FuxmzX2SAEqnw%3D%3D|tkp%3ABk9SR4iN7OSiaA

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.