DT125R FORUM

Fair play that's mint.

Hello

Welcome to the forum

Yes, photo uploading is disabled as I host all of this myself and imagine hosting is expensive.

Imgur was the preference, but is now blocked in the UK and therefore cannot be viewed here

But yes a build thread would be awesome.

Very sick! That exhaust looks PHAT!

I am in the process of designing an airbox blanking kit which would plug the gap up nicely and then also house the battery/fuses. Although I've only designed it to replace the DTRE/X airbox.

Hi there,

Pretty sure the RPMs as far as the CDI are concerned are determined by the pick-up/magneto.

So when you switch the ignition on and off, the powervalve does a cleaning cycle. Once this cycle is complete and the engine is running the valve should return into its closed state.

If it is not, then it's possible that the powervalve wires have been inverted and the powervalve hasn't been adjusted properly. I feintly recall this being a common problem back in the day.

Interesting, what inlet manifold are you running.

Presumably the cylinder you have is a 3BN model on there. I wasn't aware they ran a 24mm carb, I thought the earlier models ran a 26mm round slide.

If you keep having problems then it might be worth sending the barrel off to someone lile PJME to have the O-Ring conversion...

@Pilot_LC Ideal Gas Law - PV=nRT. Pressure of a system is directly proportional to the temperature of that system. So if the thermostat is stuck, then the temperature goes up and therefore the pressure. The radiator cap bleeds this pressure to the overflow tank. Ergo explains loss of coolant.

As I say, one issue is the radiator cap spring looses tension so try replacing that.

I just use a cheap Chinese one on my DTR with a temperature sensor in it and it's been sound.

Another problem could be the thermostat as given up, maybe it's locked closed so it's not regulating temperature correctly.

The DTX comes fitted with a 3MB.

It's only the very early 89/88 models that came with the 3BN cylinders.

Otherwise all years ran the same cylinder. Surprising there isn't more availability given how many of them were made etc

@Pilot_LC 600km, are you sure you used a genuine head gasket and not the cheap white ones.

And it was definitely fitted in the right orientation.

Oh wow, well you'll be pleased to know not much has changed in the last 20 years for two strokes. Port tuning is as it's always been and fuel injection came a few years ago on nothing but the most elite machines.

These bikes are a doddle to get running, so throw up any questions you may have and we'll point you in the right direction.

I mean, Athena make some quality kit to be fair.

I bought their 392cc kit for my RD and the 170 kit for my DTR. I do think they're exceptional value for money though, especially as used units are getting expensive and prohibitively costly to repair.

Have a search on here as some members have bought them in the past.

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.