Not sure if this is any help but anyway-- found an old 32mm RT something 1-2-3 carb, so took a few pics & measurements.
Airway is almost 2.4mm. Was a loose 2.1mm of my spray can long nozzle.
The hole in the needle jet is a neat 2.4mm so maybe the carb body hole is just dirty & drill shank was almost showing & if i turned the drill around the drill nose shows.
Needle jet has 159-QO on it.
Jet shroud bit, the sticky up bit sits up 3mm high.
Ok i think i just created a folder via a link instead of a separate link to each pic. Hope it works & it shows pics big enough..
photos.app.goo.gl/LBsNJAArb1R3uYkP9

Morning (UK time!) Morley.

The number stamped on the upper surface of the manifold should id what it is from. 

Morning Uncle. It has 308-E2 on the flange.
Found a list that said RT2 1971 so that's not quite right for a start & should be "72 for RT2.
Probably little change through the RT years "70--"73 but only guessing & happy to be corrected.
Not sure if this is any use or help. I see the RT1MX is a 34mm carb which i should have known.
Link below has interesting things & carb stuff or GYT kit stuff from pages 45 to 49.
davestestsandarticles.weebly.com/uploads...rt1_ridersmanual.pdf

Thank you very much for looking, rt325!! I believe that to be an rt2 carb, like you say. The rt1 piston port carbs are the ones in question, 275 or 284 stamp on the flange. Thank you nonetheless for checking that!!! And thank you for sharing that link!

So knowing that it's safe to say the rt2/rt3 carbs were open, just like service manual says.  I have 2 rt3 carbs that measure identical to what you found.

I noted the 2.5mm air jet in the riders manual. Perhaps they used the dash in the service manual, because it was the first year to not have a air jet restriction? I'm leaning towards it being open, as you guys are saying. You also have 2 references that say 2.5, so I'll pry leave it be.

The last time I rode my bike was in December, it was a 35 to 40 degree day.  Its got an rt1mx top end, and the rt1mx pipe.  Still has wide ratio enduro gears and 15/39 final drive sprockets.  Using a random vm34.  I went through bigger sized needle jets, and tried a 6dh3 needle.  Ultimately dropped down to the p-0 jet, and 6dh2 needle, 3rd clip.  310 main jet, 2.5mm slide cutaway.  60 pilot.  At 2 turns out on idle air screw.  It runs almost flawlessly, until higher rpms.  It gets burbly at probably 6500 rpm or so.  With the wide ratio Trans it's hard to get from 3rd to 4th, while keeping the engine in power band.  I agree with markt on these engines needing fuel to stay cool.  I think it's more a factor of not having the close ratio dirt bike transmission.  That would definitely overcome my issue. 

I did try a 280 main jet, and that got my rpms up.  But the plug looked overly lean with that, so I went away from that thought.  Original jetting shows a 310 at the leanest, all the way up to a 350.

Std 250 360 box has terrible ratios especially with a big overdrive jump to 5th. I liked the ratio spacing on my first DT1 with the coarse tooth gears except I broke third gear big wheel into pieces & put it out through the bottom. Used the same coarse type 250 gear cluster in later years on my 360 but broke the same gear. That was in a racing mx situation so was hard on the gears. Selector tracks used to chip off on the high point too--made of cheese I recon.

Perhaps of interest, I found an interesting combination with the wide ratio transmission.  Using a 52/14 sprocket combo, 2nd through 5th are near identical to the dirt bike 1st through 4th, with a 44/15 combo.  Check the math if don't believe me.  I tried 53/14, and it was fun.  If it just had the high gear...

I've heard of this, finally got tricked myself.. the "310" main jet I was using was an off brand. Stamped ab310. Believe I bought from Dennis kirk years ago. I decided to compare that jet to a genuine mikuni 310 . Perhaps the actual hole is the same size, but the taper is completely different. So I tried genuine mikuni jet. Guess what? No more burble up high! Nobody pry cares, but I'm happy enough I figured I'd share that! Lol

Well done and thanks for sharing. 

I'm only guessing here, but those pattern jets MIGHT be ok if used in conjunction with the same manufacturer's matching needle.