You're fine.  One float bowl vent is enough. 

Overflow is a brass standpipe in float bowl that drains through a fitting on bottom of float bowl on every Mikuni I can think of. 

Yep - I think there's some mislabeling on some of the parts diagrams. Two tubes - an air vent running to the top of the carb and an overflow in the float bowl.

I did a side-by-side comparison of the DT-1B 214-E4 and DT2/3 311-E2 - it looks to me like these are identical bodies with internal changes only. Here's what I'm seeing:

DT-1B
#1 Pilot Jet: (35) 193-14142-35-00
#2 Needle Valve ASBY: 285-14190-25-00
#4 Nozzle, Main: 145-14141-32-00
#5 Setter, Needle Jet: 214-14145-00-00 (alternative 214-14141-32-00)
#8 Main Jet: (150) 137-14143-32-00
#16 Valve (Slide): 211-14112-35-00 (alternative 211-14112-25-00)
#17 Needle: 168-14116-01-00

DT-2/3
#1 Pilot Jet: (30) 193-14142-30-A0
#2 Valve Seat ASBY: 168-14190-20-00
#4 Nozzle, Main: 214-14141-28-00
#5 Setter, Needle Jet: 214-14145-00-00 (unchanged)
#8 Main Jet: (150) 137-14143-30-00
#17 Valve (Slide): 275-14112-30-00
#18 Needle: 168-14116-07-00

Almost every internal part is different except for one part, so I've got some work to to. Following the recommendations from this post I'll use a 170 main (137-14143-34-00) and go with the alternative part numbers listed above that you folks provided.

If that sounds right I'll go ahead and track down the parts and get this machine fired up... it hasn't run in over half-a-century. For background, this machine was taken out of the showroom, raced in the desert once and blown, and sat ever since. It'll be great to see it running again.

I'd be a little careful about using those part numbers and go by the sizes.  Especially since sometimes parts lists have mistakes and are often shared with the 360 so it can be hard to tell if it's a 250 or 360 part listed.

What are the numbers on your jets, slide, and needle now?  Everything should be marked with a Mikuni stamp.You can save a lot of money that way sometimes and it it possible there was a design change and say the float valve is different so you need to get the one for your carb body.

 

Here's what my book says should be in a 214 revision E4 carb:
Main Jet  160
Needle Jet O-2
Needle 5D1 (clip position 3rd groove from top)
Slide cutaway 2.5
Pilot jet 35

The DT2 carb should have (according to the book):
Main Jet  160
Needle Jet N-8
Needle 5DP7 (clip position 3)
Slide cutaway 1.5
Pilot jet 30

The DT1 will probably run "okay" with a DT2 carb...my guess is DT2 spec carb would be richer than DT1 specs at higher throttle openings.  Just a guess though.

If it was me, the first parts I would get are the 5D1 needle and the O-2 needle jet. (Your needle jet has a "series" number stamped in it.  You'll need that and the O-2 size to find the Mikuni part.)

Slide is "richer" on the DT2 (less cutaway so less air).  Staying with the DT2 30 pilot will help that.  The cutaway - pilot jet combo mostly controls the off idle transition so if it doesn't run to your liking you could always track down a 2.5 slide and 35 pilot later.  It will probably be fine with what you have but maybe someone has done this and can advise.  (I find that the older bikes like a little more richness for the off idle transition with modern fuels)

AND THE AIR JET!  LOL

I cautioned about "mixing" jet specs...  needle and needle jet can affect main size.

And yes, you could recalibrate the DT2 carb to DT1 spec...  my guess is it will run okay with the DT2 jets, if you want to get it running with what you have.  To be a little safer you could raise the needle a groove or two.  Someone has surely tried this and hopefully will comment.

As Mark has already said , getting part numbers off internet sites can be a bit tricky , especially on shared 250 / 360 pages .
A couple of the part numbers in your list were incorrect . The DT1 and DT2 share the same 2.0 valve seat  168-14190-20-00 .
The correct throttle slide number for DT1 is 211-14112-25-00 .
The part number you had for the stock 160 MJ was correct , but you had it down as a 150 . Probably a typo I'm guessing ,
but the early 68's did use a 150 main .
If you're going to start with a 170 main jet , then That's not really important .
There were errors in DT2 base setting numbers too , but no point in detailing those as they're not the parts you're looking to purchase .

 

Nobody “seems” to be talking about how the bike runs..


I tune Therefore I Am…

asco

I bought the 311 carb in very good shape but I have no clue how it was tweaked. And I picked up some VM26 parts from a pal of mine. So I have a 'kit bag' of stuff.

Here's what I have in the carb as it stands:

Pilot Jet: 35
Slide: 25 (which I assume is 2.5)
Valve Seat: 2.0

I'm good in this area.

I have two needles. One is marked "5DP7" and the other "Y1" (which is in a bag labeled "DT-1" but I can find no reference for it.

I can't see what the Needle Jet is until I push it out - doesn't want to budge. However, it's easy to find an O-2 if it proves to be wrong and the 5D1 needle to match.

I'll swap the 150 main for a 160/165/170 per your guidance to get started.

Now... the "air jet" has been mentioned. Where is the heck is it? I can't find it anyplace on this carb.

The Y1 needle is from a Keyster carb kit . Do not use !!!
There are a lot of different style O-2 needle jets around , but you do need the correct type .
Stick with the OEM part number and you won't have any dramas .
There is no specific air jet . There is a air drilling hole feeding the Needle Jet , but no adjustable jet as such .
There are some carbs that do have a removeable air jet , but this carb isn't one of them .