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It sounds to me like the relay. So the starter motor button isn't wired directly to the starter motor as the starter motor requires a lot of current.
Instead the wire is connected to the relay and the relay activates the starter.
So I'd look in that general vicinity, sounds like it's starting to go faulty, which isn't bad considering it's age and the high amperage that it is subjected to.
These bikes are getting to an age where the clutch cush drive rubbers will start to wear out.
It's possible that this is where the rattling is coming from.
Whip the clutch cover off and try and rotate the clutch basket by hand. There should be no discernible play in it.
These rubbers sit behind the clutch basket
Sandwiched between the primary gear.
There were chaps on here that used to do something very similar but to the UK. Go down with a van and collect 5 or 6 bikes at a time.
Definitely worth while if it means you get the right bike.
My Dad imported a Lambretta GP from Brussells a few years ago, was no hassle.
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.
@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
that's it now then.