DT 125 R '88... New project
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Okey, owners manual says that bore is 56mm and stroke 50.7... Does Athena 170cc kit fit into this?
By the way, someone claims that this bike std carb is 26mm mikuni, here's snap from owners manual, and it clearly says TM28SS:
Isn't TM a flat slide and VM round slide? Carb that I took away, was 28mm round slide! Isn't that a VM28?
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Again, if your barrel was the 3MB this would be correct.
It's not it's the 3BN which I think were off really early DTR's before they swapped the carb for a 28mm and a 3MB barrel.
So no, Athena 170 kit is not designed for this engine. You will need to put a 3MB connecting rod, assuming it's just the rod length that's changed, or a 3MB crank.
It's not anything big, I just thought I'd mention it incase you wanted to rebuild the engine, it is ever so slightly different.
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@jgr72 Yeah that was my thought exactly way back way.
Approx 133cc if my memory serves me correctly. Or that might have been if it was bored out.
I know it's only minor, but you wouldn't want to throw out the characteristics of the engine.
I'm pretty sure Yamaha swapped the configuration for a reason.
So if it were me, I'd throw a 3MB crank in there and use a 3MB head and barrel.
But I have no proof to back this up as beneficial.
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Or something bigger? If I have to dismantle whole engine in pieces... why not build up with the biggest available pieces
WR200 or DT200/230 crank, barrel and piston!? I've seen that swap somewhere... Or Athena 170/180cc Its the same job anyway... only some more money to waste 
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@jgr72 Might as well just swap out the engine when you get to that point.
In my opinion, for the bike you currently own. Leave it as original as possible. It's a gorgeous bike in standard trim, any modifications to it is just criminal if you ask me.
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@Calum You're right about keeping this bike original... but since I'm only a human, and I have only one bike that should do all that I want... I will try to keep it look as much original as possible... You simply just can't have too much power... at least this small engine... But to be honest, I can't see very big difference, when accelerating from 0 to 80km/h, when I compare it to my ex XT600... After about 80km/h XT600 would disappear into a horizon...
Is there a inlet that would rise carb a bit? few centimeters would rise it over the clutch thing... And also inlet should have more angle towards to airbox in order to duck around rear shock...
I can't even find inlet bolt pattern... It's not so hard job to do by my self... Or it would be nice to know which inlets would fit direct to 3BN engine... Then I could try to find one from somewhere...
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@CYBER-NINJA It's werid people say this, A boost bottle and the YIES chamber design from Yamaha never increased horsepower.
All Boost bottles or 'resonance chambers' do is help to smooth out 2stroke induction, which is of most benefit at lower air speeds... Low to Mid RPM running.
@jgr72 The WR200 inlet wont raise the height of the carburettor, but, it will make it clear the Clutch arm and give better clearance around the Shock Absorber.
Also for the love of GOD, do not chop this bike around anymore!!!
I would get rid of my DTR for your 'Endurance Blue' 3DB1 DT125R. They are one of the most desirable models.
See my build thread for carb placement, and note that there is no clean way to upsize carburettor bodies!
EXCEPT. using a (TM30ss) That will just about fit in with the original 125R inlet tract.
https://dt125r.co.uk/topic/77/yamaha-dt125r-01-running-project/73
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@Darty Very interesting, I get the tech behind adding the boost bottle and yes it may never increase HP, which was not it's designed purpose as you have correctly stated. All I can do is speak from experience and shared this. By removing it that must have changed the air-flow and the mixture, as the bike was definitely slower with it off. Yamaha obviously did a lot of testing and choose to run this system for optimum performance. All I can say is that the bike ran better with it on, so I kept it on. The only way to really know for-sure is to test with and without the bottle and pick the set-up which gives the best results for your riding style.
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