DT125R FORUM

You must be able to just buy some double sided foam tape somewhere and just repply.

@pilot_lc That's amazing! Fingers crossed that's it now then.

@Pilot_LC Yeah, I wrote a blog on doing it here: https://dt125r.co.uk/post/23

It's only a gentle skim, it won't cure completely warped heads.

Be sure to the deck of the barrel too.

Several options

Can you not skim the head and barrel and remove the imperfections, then space the barrel with two bottom gaskets?

Can you not get yourself a reusable copper head gaaket. They used to be all the range a few years ago.

You could always contact an engineering firm like PJME to machine an o-ring into your setup to bypass the imperfections.

https://www.pjme.co.uk/acatalog/Yamaha-DT125R-Head-Gasket-O-Ring--5866.html

I skim both the head and barrel.

https://dt125r.co.uk/topic/11/how-to-i-gentle-skim-your-head-barrel

The tube perpendicular to the filler neck goes to the coolant overflow bottle.

As the coolant heats up, it expands, it needs somewhere to expand in to, this is the coolant overflow bottle. As it cools, it contracts and pulls a vacuum and draws the coolant back into the coolant system.

The radiator cap is spring loaded (I believe it's 1.3 bar) and that pressure is needed for the coolant to vent into the overflow bottle. You shouldn't be ditching this to the floor, it goes to the coolant overflow bottle.

As seen in the picture above.

Can I confirm, you're talking about the overflow tube right. This is routed to the overflow bottle. You have to allow for water expansion/contraction into and out of the expansion bottle. Don't just route this to the floor.

Secondly, a problem I hear is that the radiator cap looses tension over time. It should be rated to 1.3 bar but they weaken as they age. The result is it's unable to maintain spring pressure and erroneously overflows coolant.

So be sure to check both things are in agreement.

Oh that's pretty standard on those Mikunis sadly. Very common.

Jeez how bad is the head to have warped that much? Depending on how much they skim it by you may need go offest with a thicker base gaaket.

Hi @yennie ,

That's cool and I am glad you've managed to get something working for your setup.

I am working on something similar to just add a slight angle to the inlet manifold so pod filters don't foul the shock absorber.

They say it's mechanical but the description sounds electrical and they're adamant it's not

I still maintain it's electrical related, ignition timing, static angle, etc.

But I am not familiar with the ignition system they're running and/or how it's been wired together

Okay, well going by what you're telling me, if we assume the CDI system is not at fault, then that leaves you with the ignition coil, spark plug and lead.

I really would just put a brand new OEM ignition coil on there as I am concerned you've fitted a Chinese one on there.

I fell into this trap when I did the rebuild on my DTR and I bought a 'Racing Coil' and it worked fine for like 15 minutes and then would be saturated and not able to maintain spark.

I had just rebuilt the bike and everything was new on it and it took me until my brother bought his RD350 with the same problem and the same Chinese coils for me to tweak. Bought brand new OEM coil and the problem went away.

Another common problem that sounds like yours is having water in the exhaust expansion chamber.

Make sure the inlet and exhaust are completely clear of any debris

You can eliminate the airbox to rule this side out, if it's only for a short while and you don't live in an overly dusty region then you'll be fine.

And give your exhaust a thoroughly good clean to decoke and remove any particulates there

If you have the stock RE exhaust, these have a honeycomb catalyst inside them which must be coming to their end of life by now, so an aftermarket DEP pipe would cure that

Well this makes it challenging to diagnose if it's got a custom wiring loom on it.

Have you ever had it running right. When I hear custom my first thoughts are, well it's probably something to do with that then sadly. As these bikes are very simple, the things to check are the basic two stroke principles:

• Compression
• Ignition
• Fuel

And if you've got all those then it'll go.

So what's the compression of the engine?

If it's got a custom ignition system then what's the static angle been set to?

I wouldn't go round forcing it to start, it should start first/second kick with choke and anything else you're going to do more harm than good.

What head gasket did you use?

If the new head gasket was white in colour then it's probably the same culprit as the cheap head gaskets simply do not work. Use genuine, Athena or Vertex head gaskets only.

Did you install the head gasket with UP facing you? The head gaskets can be accidentally fitted upside down, which again will cause similar problems.

When you say New coil you mean new genuine coil. Again the knock off chinese Racing coils DO NOT work. So only use genuine ignition coils.

I don't know what a HPI ignition is, but if you can source an OEM ignition system you can rule out faulty electronics.

Common problems on these engines will be things like, waterpump seal leaking into crank case and then crank seals leaking into engine combustion chamber. Both are pretty obvious but will cause running problems. And when I say common, they don't come up that often as the engines are pretty darn bullet proof.

Okay, a few more NOS parts ordered and now the primary drive gear, clutch basket and generator nut all torqued to spec!

All 6 TZ750 clutch springs fitted with brand new clutch plates and NOS OEM damper rings installed.

I also replaced the factory pressure plate with a gorgeous billet RDLC Crazy pressure plate.

It's said to have better oil flow and looks to have a fair amount machined out of it, but I was surprised to see it's slightly heavier than the factory setup.

This milestone marks the completion of the bottom end There's just the matter of the water pump to install, I was really hoping to get a Chariot Performance uprated one, but they're no longer manufacturing them. And then there is a company that makes a stunning carbon fibre generator cover/chain guard. I did have my eye on a Chariot Performance one, but again they seem to no longer be making them sadly.

The cylinders are booked in with Mick Abbey for some mild porting work, then the heads need to be sent off for machining.

But once that's done it will mark the engine work completed for this project and I will turn my attention to the frame.

The frame has now been moved into the garage and I'm just trying to figure out how/where the steering damper should be fitted!

I do need to get back out on this bike! The front brake disc failed (annoyingly as this wasn't cheap) and the battery died over winter, even though it was on trickle charge, again very annoying.

I did manage to get some nice bits for this bike, but I've only manage to get around to fitting one of the parts as the bike is in a storage unit and I don't have all the tools there to do all the bits.

Firstly I have this beautiful VHM gold skull cap.

I look forward to getting this fitted.

I also have a pair of these beautiful carbon infills for the side panels (if I can remember where I've put them). I will fit these when I do the skull cap as it requires taking the fairings off.

This week a special parcel arrived from Italy, which was a beautiful carbon fibre rear seat infill to replace the FRP one I had there originally.

It almost looks plastic dipped in that photo, but I can assure you it's the real deal.

Very happy with the fit and finish (although the seat wasn't placed down properly in this photo, hence the gap).

Just buzzing to get out back on it now that summer is here!

Forum patched and updated. Fixed some database corruption issues which was having a knock-on effect with emojis so hopefully they're working now.

@Rallyfinnen It's annoying that images get ransomed. I simply don't have the bandwidth HDD space and/or money to host images.

That said, I have migrated my images to the server so that the issue of images being ransomed goes away for me.

Oh that's really awesome. I certainly hope it works out for you though. I think I'm done with the DTR platform for the time being and am concerned with my RD at the moment. But I am building an LC motor which one day may be transplanted into a DTR chassis...

@vtrtomuk Yeah, just have to enjoy it for what it is sadly.

I have had mine ported and got lots of supporting mods to boot. It goes alright, but my Aprilia decimates it completely. Still nice bike to have and you can get some improvements out of it.

Hi Glenn welcome to the Forum.

It's very quiet on here these days, everything migrated to Meta a long time ago, but I feel the real enthusiasts will remain here

Sounds like you've got a wealth of experience with these bikes, almost feels criminal to be breaking them nowadays though, price of them are soaring.

Hi there,

You're literally describing the characteristics of the big bore engine. It's not going to rev like the OEM setup, a big bore kit will drop over revs and this sounds like it's in the right ball park figure.

I'm not saying 9500 is the limit, but this is definitely past its peak power and I wouldn't expect any power gains past here.

The next step for retaining revvibility will involve more drastic tuning.

• Zeeltronic CDI Ignition System
  • Allows you to have a fully derestricted ignition system
  • Customise powervalve for the Athena kit
  • Squeeze out a few more RPMs
• Cylinder porting
  • Greater volumetric airflow through the cylinder
  • Allowing it to breathe easier
• Transfer window porting
  • The transfer windows most likely need porting due to the larger bore
  • Gasket match the cylinder to the cases
• Porting the cylinder base removing the obstruction to airflow from the reedvalve
  • Air flow is greatly disturbed by the cylinder spigot protruding into the intake
• Fit VForce4 Reed Block from Blaster
  • Proven to increase mid-range and overrev performance
  • Boyseen dual stage reeds can also help but seeing as your requirement is literally at the top end of the powercurve then you don't want dual stage
    

Just bear in mind, you're now demanding a lot more from the engine than stock and seeing as you're seeking peak power you're going to want supporting mods.

• Uprated clutch springs to avoid clutch slipping
• Forged connect rod to resist rod stretch/fatigue
• Forged light weight piston to withstand the demands