Noob

[Rat80y]

Hi everyone

I got myself my first bike, a DT125 R.

It seems to have a issue reving past 6 6.5k, I think it was still cold and the choke was on, but he is adamant it was off. I was going to see if the pv was doing its cycle when turning the bike on

I have the parts to do a plug and fluid change but was wondering what else it could be?

Any help appreciated

[Rat80y]

Its a 2000 model

[Calum]

With the choke on and it being cold, I'd be reluctant to rev it past 6500.

The 2000 models were heavily restrictive, so going over it all and ensuring it's full power and healthy would be where I'd start.

See @scrimsmustang's guide for derstricting.
https://dt125r.co.uk/topic/3492/yamaha-dt-125-r-derestriction

Do a compression test, make sure the engine's healthy. Check all the air ways, that the exhaust is free of water/oil. That the airbox is clear and the filter has been changed. Check the carb and jets make sure that they're all clear and not blocked.

I'd pin the powervalve open for the moment, just to eliminate it from being a problem source. This will drastically reduce power low down, but should rip roar to the red line.

[HOTSHOT III]

@Rat80y I don't have a great deal of experience with the 2000 models with (usually) 5-wire servos etc. so what @calum said.

I'd definitely do a full carb clean including the emulsion tube (the brass tube the main jet screws into). A lot of people (including bike shops) miss this and don't realise it comes out because you have to screw the main jet back in without the brass washer and tap it gently to remove it from the carb body. The space between this and the carb body gets blocked with moisture, dirt etc and blocks more and more holes in the tube (which is how the air atomises the fuel) until it just starts fourstroking and won't rev out one day as this controls the mid-throttle fuelling. Just chucking it in an ultrasonic cleaner usually isn’t enough; you have to actually remove everything from the carb body, physically make sure all the jets and air passages are clear, then reassemble. Make sure the air supply to the emulsion tube is clear as well, it's the small brass tube on the right of the carb body just in front of the carb-to-airbox rubber. You should be able to blow through it, but only just.

Oh and BTW the float height on the flat slide TM28SS carb is 15.5-16.5mm despite what Haynes says, they got their TM28SS mixed up with the earlier VM26SS round slide carb whic was only on 1988 DTRs. Hope you get this sorted buddy.