Old Brown

[Team Junk]

Looks like the pipe is the mx pipe . Yea. The head appears to be the 400mx. Thinking they swapped the mx top end on to the 76 dt bottom end. Tank is a it400 plastic tank. No rust in tank to deal with. Petcock looks pretty good but seller said he replaced the petcock rubber but he thinks it's not the right one because it takes pliers to move it
This looks like a wild ride ahead.

 

[RustiePyles]

I think 77 is the first year for CDI oN the IT.
You’ve got a 75,76,77,78 DTIT400MX, Johnny Cash would be proud.
If it is an MX/YZ top end on a DT/IT bottom end it will be one squirrelly torquey bike. YZ/MX Powerband with all the traction, torque, and grunt of the IT flywheels… what’s not to love?

 

[Team Junk]

I'm thinking I need to do a big good deed tomorrow. I think this used up my good karma alotment .

 

[YamadudeXS650C]

I've had several DT's. Lovely bikes. Maybe we need a "DT club?"
I know @RustiePyles is building a 175 and @YamadudeXS650C is putting together a 250. I'm working on a '74 250 bitsa bike. Frame is sandblasted and I've started some repairs on it.


View attachment 192836

A DT Club? I'm in !
Got my '73 DT3 250 running well this spring and have been blasting around my 4 back acres regularly. Loads of fun !

 

[Team Junk]

That green is beautiful.

 

[YamadudeXS650C]

That green is beautiful.

One of my favorite things to do is to quickly circle around back to where I was riding and smell the oil-burnt fumes. Like heaven !

 

[Team Junk]

It sounds great. Now I really want to crank mine up. I love the sound of 2 strokes. This one should be awesome with the factory chamber.

 

[Team Junk]

One of my favorite things to do is to quickly circle around back to where I was riding and smell the oil-burnt fumes. Like heaven !

Yep. I need to start looking for bean oil. I hope they still make it.

 

[YamadudeXS650C]

Yep. I need to start looking for bean oil. I hope they still make it.

Looks like Klotz still has it available.
You could cook up some french fries at the same time !

 

[Team Junk]

Have to admit it's nice to run a two stroke that runs on premix from the factory. Was always a little worried about running a injection bike on premix.

 

[Team Junk]

One of my favorite things to do is to quickly circle around back to where I was riding and smell the oil-burnt fumes. Like heaven !

Heaven is the first lap in a pack of 40 Yamaha 350's all running a rich mixture bean oil.

 

[Team Junk]

This is what Yamaha recommended for this bike back when it was new. I forgot the fact they still build yz's so they still make it. Life is good.

 

[Team Junk]

The reeds may be a little tricky. The carb and reed valve look like they might of come from the dt400 donor. The outside diameter of the engine side of the carb matches my VM34's . The 32-36 are the same body . The MX according to unworthy sources has a VM38 which I think are quite a bit larger.

I pretty sure the head is the original mx. the jug and carb may be DT parts.
The pipe is the MX chamber so the important go fast parts are there. The MX jug I'm pretty sure would be the same casting ported more aggressively.


From my research today this bike falls in 75-77 magic range before the EPA started throwing fits.

Seems to be the high point of the Yamaha Enduro line. Monoshock,CDI,big carbs, decent forks etc.

I think the mx pipe and head added to a DT engine will preform pretty well till it runs out of carb. I don't plan on redlining a 40+ year old motorcycle so may be a good compromise.

 

[Team Junk]

This site is an excellent resource for parts for vintage 2stroke parts especially plastics.

I'm rather impressed with the variety of plastics they sell.
Ordered my first part for the thing. A cheap repop petcock to use while I figure out what the PO did to the original petcock.

Surprised to find wiring for the headlight in the main loom. Maybe they used the same loom for the DT and MX ?

 

[RustiePyles]

The reeds may be a little tricky. The carb and reed valve look like they might of come from the dt400 donor.
I pretty sure the head is the original mx. the jug and carb may be DT parts.
The pipe is the MX chamber so the important go fast parts are there. The MX jug I'm pretty sure would be the same casting ported more aggressively.
.

I'm pretty sure the V-Force reed cage should still fit.
It could be a GYT Kit head and pipe, in 76-77 they were basically just MX parts.

Surprised to find wiring for the headlight in the main loom. Maybe they used the same loom for the DT and MX ?

But does it have an aux lighting coil?

 

[YamadudeXS650C]

The reeds may be a little tricky. The carb and reed valve look like they might of come from the dt400 donor. The outside diameter of the engine side of the carb matches my VM34's . The 32-36 are the same body . The MX according to unworthy sources has a VM38 which I think are quite a bit larger.

I have this spare reed cage from my DT3 if you need one.

 

[Team Junk]

But does it have an aux lighting coil?

The $64,000 question. I don't think the mx cdi did. There is provision for one on the backing plate.

I'm assuming that something bad happened to the original MX motor. If I was swapping in a DT motor I would of used as many of the MX(GYT) parts that I could and the CDI. Would of made the wiring a breeze. So I hope that's what transpired here. With a PO there's never any telling.
Last night was a work night so when I get up this afternoon I will know more.

Plan 9
1) Put strobe on and see if it has spark.
2) Pull magneto cover and see whats in there.
3) Check the Gas.
4) If gas is ok then see if it will pop.
5) Go to town and see if Yamaha has the Yamalube 2R in stock to make fresh gas.
6 Order mixing cup.
7) Take a bunch of photos before I dig in further.
8) Make fresh gas.

Somewhere in there build a stand to get the wheels off the ground.

 

[Team Junk]

I have this spare reed cage from my DT3 if you need one.

I appreciate the offer .
I'm kinda going slow on this .
I think I will be able to find NOS reeds to rebuild the MX reed assembly.

 

[Team Junk]

What I wanted to be when I grew up.

In Texas when I was growing up we had a high school pep rally Friday mornings first period. Could care less about HS football. About 20 of us used that as a hour long opportunity to rat race through the maze of neighborhood streets around the school on our enduros..

This is the bike that I lusted for. Have talked about it to friends for years.

Now I end up with a 4 year newer model of it. Amazing good luck.

 

[RustiePyles]

I appreciate the offer .
I'm kinda going slow on this .
I think I will be able to find NOS reeds to rebuild the MX reed assembly.

If you're determined to use the OEM reed cage, I can't stress enough that the Boysen replacement reeds are junk. I often find with the OEM metal reeds that flipping them over works pretty well. While I'm not usually one to go replacing OEM systems with "upgrades" when the OEM systems are sufficient. Reed technology in the 70's was not near what it is today. Even putting a set of V-Force carbon fiber reeds in your OEM cage will make the bottom end WAY more useable and the power band way smoother.