Hello Yamaha owners,

4 months ago I bought a very nice condition Yamaha DT125 R, 2004 plate.

When bought, on the ride home, and for the first 2 months it was supremely quick to what I had been used to on my 50cc moped. It went way off speedo (an indicated 85mph), and popped up ferociously in first and second gear when given a lot of throttle.

It came fully de-restricted, with full DEP system (de-restricted). I believe the rear sprocket was also 1 tooth less than the standard, before I changed it to a larger sprocket (by two teeth, resulting in my current rear sprocket 1 tooth larger than standard dt size).

Between 9,100 miles and 12,300 miles the DT has seen a significant loss in power, resulting in a measley top speed of around an indicated 70 - 75mph.

The engine doesn't sound as crisp as it used to, and it takes a real long time to pull me to top speed in sixth gear. Throttle isn't as responsive as it used to be in terms of power delivery. It just has no power anymore down in the bottom of gears where it used to, and I just cant feel the power band kicking in anymore, it just feels flat, and nasty!

I have to admit I haven't done TOO much maintenance to the bike, air filter gets regular cleans, so does spark, however I havent touched the carb.

Would anybody suggest having a clean of the carb and clearing of fuel lines?

Any other suggestions? I fear that if i go back to using a smaller rear sprocket I just wont have any power low down in gears. (Because ultimately I'm aiming for that original 85mph+ top speed).

I do ride the bike relatively hard, but surely it isn't in need of a rebuild just yet?!?!

All advice is welcome! Thanks in advance, Chitty.

Have you been eating too many big dinners :lol:

Have you been eating too many big dinners :lol:

lol if only it was just pork pies..

perhaps i just shouldn't expect a single drop of reliability from a two stroke engine?!

...but seriously..?

It's bloody annoying not being able to overtake a ford transit VAN swiftly anymore on A roads...

12000 would be overdue a piston ring change, I would be doing it at 10k max, can you do a compression test?

Would anybody suggest having a clean of the carb and clearing of fuel lines?

Wouldnt do any harm to give them a clean just incase there is a parcial blokage.

Have a lookie at your PV cables ta see if there slack or broken and the wee junction box further up and see how things are !

EDIT: i also agree with OG in the 10k mile rings been changed

perhaps i just shouldn't expect a single drop of reliability from a two stroke engine?!

:o Sacrilege :o :o

Its time for a top end inspection Chitty at 12k longer if its had an easy life but 85mph i think you have riden it well. I think im due new rings cause i "forgot" to run them in

Ok, I will get on the case of finding a compression tester.

If i replace the piston ring, would it mean changing the piston too? Or not necessarily, depends on it's condition i suppose??

I suppose it could be a number of things, but I'm wondering if just replacing the ring would be worthwhile?

sorry not too knowledgeable on this subject

appreciate all the comments however

Wouldnt do any harm to give them a clean just incase there is a parcial blokage.

Have a lookie at your PV cables ta see if there slack or broken and the wee junction box further up and see how things are !

EDIT: i also agree with OG in the 10k mile rings been changed

Thanks, I'll look over the cables and get back to ya, didnt think aboot power valve..

12000 would be overdue a piston ring change, I would be doing it at 10k max, can you do a compression test?

is a compression tester something you can just buy, that wont cost too much? are they specific to 2 stroke engines or a universal thing?

if my compression is too low, and i resort to top end rebuild, do you have any ideas how much a garage would charge or how much a kit would cost?

thanks

You can just buy a compression test,,,universal you should be reading 95 psi or over.

You might get away with just changing the rings but while its apart you can check piston and barel for ware.

Is she hard to start

http://cgi.ebay.co.uk/PETROL-ENGINE-AUTOMOTIVE-COMPRESSION-VALVE-TESTER-TOOLS-/390234169309?pt=UK_Diagnostic_Tools_Equipment&hash=item5adbc4dfdd

god thats cheap, cant tell you if its any good...there's a saying 'you get what you pay for' i'm sure youv'e heard it. However i'm sure you are quite capable of finding one.

Trouble with the DTR is it's a right b4strd to do due to a severe lack of room and if I remember right quite a few things have to be removed first. also they say it is best done when engine is hot. a good engine will show over 100psi...mediocre...say 90 psi