The float arm in my carburetor is the flat style shown for the DT400B, not the style shown for the DT250B where the float arm has loops on the end to install the floats on (I'm assuming thats how they should work). The carb does have the easily removable main jet in the float bowl that is correct for the DT250B.
Is this some mid year change or has someone been into this carb before??
The float arm level is right at 68mm when measured at the slot on the middle of the carb body as shown on figure 4-2-21 on page 80(page 88 on the download) of the DT250B/400B service manual. 
Were there issues with the DT250B version of the float arm? I can imagine that they could be somewhat of a pain to assemble.
Just curious. Everything else on this bike does appear to be oem AFAIK.
This engine does start now.
Tires and tubes should be here today. I'm going to have to do some homework on messing with the bead locks when changing the rear tire/tube.
The rest of the needed parts have been ordered. 
In two weeks this thing should be ready for a test run

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hopefully!!



 

If I remember correctly, the black floats should ride on pins in the bowl and are separate from the float arm. 

I can't remember ever seeing any Mikuni that had "loops" that you hook the floats to? 

If the source of confusion is a "parts diagram", please keep in mind that the diagrams are not always correct and I don't believe were never intended to be used for assembly...  many bikes have been assembled wrong by using the diagrams as a guide. 

One thing that you can do is search for the part number on ebay and look for pictures...  keeping in mind that many sellers don't list parts (especially used) correctly.  For something like a float arm, there are probably several NOS in the NOS packaging. 

yea, I'll just run it and see how it goes but both the parts manual and the service manual show pics of the float arm with the loops.
Fig. 4-2-1, page 74 (page 82 on the downloaded DT250B/400B service manual)
Fig. 13, page 35 (page 44 on the downloaded DT250B, DT250C, DT400B, DT400C Yamaha parts list)has little line showing float pins going into loops of float arm

I don't know how you're seeing "loops" in the picture in the service manual?  I sure can't. 



And AGAIN...  parts diagrams are not assembly diagrams! 

Some artist may have added those or something...  The floats are captured by large vertical pins in the float bowl.  If you also attached the little pins on the sides of the floats to loops on the float arms, the floats would jam and could not move up and down freely.  It simply would not work. 

I'm stressing this because you don't seem to be getting the message that it's often a mistake to use the parts diagrams (drawings) to assemble the bike.  Most common mistakes I've seen in assembly is clutch thrust washers and the order of the clutch disks...  I'm not sure any of the "exploded" clutch parts diagrams are correct...  the engineering "blueprint" drawings in some manuals are correct as far as I've seen.

Edit.  I was looking at the wrong page...  you were referencing another "artist rendering" a few pages before the pictures.  I looked for page 82 of the manual, not page 82 of the pdf. 

(Pic I posted above is on page 81)  I have too much going on and rushing too much right now.

Here is 4-2-21...  page 80... with a clearer view.  It's the 250 as you can clearly see the o-ring on the jet setter.