DT 125 R '88... New project

[andrewj1680]

How did this setup workout for you?

[jgr72]

Actually I haven't tried it yet... But it supposed to be a good setup!? Original carb feels a bit out of right setup... It feels rich in mid rev and it won't rev above 8k... top speed is hardly 110km/h. But I have no intention to do anything for it... new carb is only waiting to "step in"

Still waiting for that oil hose nose from ebay... It's taking many weeks from china to europe sometimes... Meanwhile I had to do something... I drilled a 2.5mm hole for oil feed hose nose and tapped M3 threads with a screw drive style handle... M3 is so small and alu so soft that it was an easy to turn...

[jgr72]

Finally hose noses arrived:

I bought few of them in case I need one in future...

There it is... I also added some "thread glue":

/20170704_092559.jpg)

Okey, now I have all I need to change the carb. But how about the carb throttle cable? Is it a straight swap, or do I have to make some modifications? I've been trying to find answers from google...

[declan]

@jgr72 it should fit but the only way to know for sure is to actually try it

[Calum]

For my dellorto VHSA carb the cable needed modifying.

[jgr72]

Yes, it fits, but I need to strip throttle cable about 30mm... Sorry that my phone focus to the engine, and not the cable :

But there it is now:

TM30 comes quite close to clutch, it can't be installed straight... must be a little bit askew... Maybe some other intake would give better position?:

Next problem is this:

It wouldn't line up nice... Maybe DT230 Lanza intake would correct this problem?

Or then I just make my own boot for universal air filter, and forget the whole original airbox... I tried the bike without air filter and it runs quite nice, no torque loss at low rpm, and still have more power at high rpm... feels good, even I might not have the best jetting setup jet... If I remember right, the best main jet was 135 etc...

But... I can't ride without an air filter, and I need to fine some solution that I can ride with while I'm planning my next move:

I sprayed urethane, and "glued" 50mm alu pipe to the air box This wasn't a very professional style, but its easy to remove and airbox is still original, while I don't know what to do next

[Calum]

@jgr72 You are running a 3BN barrel.

They have slightly shorter strokes with bigger bores than the classic 3MB. Be mindful of that when it comes to engine rebuild time.

[jgr72]

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?

[jgr72]

Now I'm confused, manual of an 3MB page 84 says that 3MB is also 56x50.7:

link text

[Calum]

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.

[jgr72]

Okey, barrel have 3BN00 stamp on it... I think I will rebuild it someday... I'll get back then Hmm... 3MB crank & rod + 3BN piston and barrel would give a little bigger engine

[Calum]

@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.

[jgr72]

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

[declan]

@jgr72 id love to have a spare dt to tune

[Calum]

@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.

[declan]

@Calum I have a 3mb barrel and a 3bn bottom end what does this mean I don't understand the codes?

[Calum]

@declan That's just normal.

[declan]

@Calum ahh okay thanks

[jgr72]

@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...

[Darty]

@jgr72 There are no direct replacement inlets for a DTR engine.

Believe me I've looked.

Why don't you try modifying a WR200 inlet? They were made for the Mikuni TM30ss...