DT 125 R '88... New project

[jgr72]

A little update... Today I fixed front brake... Sealing was worn, and it would be only matter of time, when the brake cylinder would stuck totally... It was already a bit lazy I think... I did it just in time, there ware some corrosion in brake caliper, but I used sand paper and decide that it's still useful... Piston was in excellent condition... Old brake fluid was quite black and shitty... perhaps original and nearly 30 years old? Then caliper rebuild with new sealing and gasket... Tomorrow I have to bleed air away from the system... It looks like I have to use pressured air to force brake fluid into caliper... Brake lever is now doing nothing Sorry that I was too lazy to take any photos...

I found myself from ordering a new carb... Mikuni TM30... and it's on the way already And earlier I also ordered DT230 Lanza version of carburetor -> air box joint... Lanza item should be direct fit to TM30 carb and maybe some minor modification to the original air box... On the engine side, the diameter difference (VM28 vs TM30) is only 1mm bigger, I assume it will fit to the original intake rubber... TM30 is also 5mm longer, but that shouldn't be any problem...

Anyone have idea for right main jet? 160? 170? 180?

Silocone tubes arrived yesterday, I will replace all 2-stroke oil feed tubes from oiltank, to carb...

[jgr72]

Today I changed leaking autolube hoses to a silicone one... I ordered them from ebay many weeks ago and they arrived few days ago... It was an easy job to do. Tank to autolube pump hose was nice fit with 5mm silicone hose. Autolube pump to carb was nice fit with 3mm hose. But be aware if you bleed whole pump empty, it might not be able to suck oil from tank!!! Be careful when you start the engine!!! I have to squirt oil direct in to the pump and open air screw in order to get the air out from the pump. Here are from photos from that job...

Dissolution:

Pump to carb hose size:

Tank to pump hose:

Pump to carb hose in place:

Tank to pump hose in place:

Ready to ride:

[Calum]

@jgr72 Nice clear lionesis what I like to see.

Keeping an eye on that oil

[jgr72]

Yeah, actually it was nice to see how the oil travels in pump to carb hose... I had red oil and air in that hose, and it travels with a rythm And it was easy to see how it works when you rev the engine...

[Mightyman]

Very nice, hopefully others can come across this thread if they want to swap their own hoses out for clear ones.

[jgr72]

Thats why I took those photos! Internet is a information source

[jgr72]

Santa Claus came early this year I received TM30 & 230 Lanza air joint in a same day It's a great match with those two! Let's see later how it will fit into DT125R airbox Sadly I don't have any main jets between 150 and 200 range... I've been told that 170 might be right main jet to start from... Also need to drill a hole to the TM30 for oil feed anyway, and don't have that hose nose yet... I'll come later on with pics when I'm installing that... Here are some pictures of todays treasure:

Yamaha DT 230 Lanza carburetor -> air box joint:

It a great match together:

[Calum]

@jgr72 Looking good buddy!

[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":

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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.