your bike sounds badass!
I have a DT1 ('71) and it sounds quite similar
and unlike my DT360 which idles okay, the 250 idles even better, never wants to die at a quick stop...

It sounds good, but if it's idling that high with the screw all the way in then it's worth making a post about it (or working on it in this one) because something is wrong, it could have an air leak somewhere, do you have a newer o ring between the carb and the reeds?

Starting on one kick cold, if it's been turned off for some time with the carb drained, is a bit odd. Typically they take a couple kicks just to get fuel primed if the carb was run dry before parking.

I didn't pick up on the air screw being turned all the way in, definitely points to a clogged primary circuit or an air leak

still sounds killer 

Thanks for the sound checks! It makes me happy to hear experienced riders say that it sounds good. I love how it sounds personally but don't know how to determine how much rattle adds character and how much means it is time to rebore.

I want to get to the bottom of the idle issue. Main obstacle being my lack of knowledge. As of yesterday the bike wont start anymore. Seemed like just wasn't getting spark which happened twice and was easily fixed with a new plug so didn't concern me much. But after putting in a new plug it still wont go this time.

What Darnim said about starting on a cold kick might be related to the 'carb flooding when the petcock is off'. I was told about this problem but unfortunately don't understand what that means in a useful context. I understand the carb is getting gas when it shouldn't be but the 'so what?' I don't grasp. I had just put a towel under the bike in the garage and accepted she was a little bit leaky on account of her age. That worked until yesterday.

Does that help diagnose the idle issue at all, or just two unrelated problems?

THANK YOU ALL SO MUCH!

The quote feature I think is temporarily non-functioning but I want to answer this:
do you have a newer o ring between the carb and the reeds?

No. The only thing I did to the carb was blow some air through it. Didn't adjust it or even look inside.

It's worth putting a new o-ring between the carb and reed block, #41 in the diagram below, part #93210-37140-00

Sounds like you have not been into the carb, I'd open it up and clean all passages and replace o-ring #7, it's prone to rotting and needs to be in good shape for it to run well too, part #214-14147-00-00

www.partzilla.com/catalog/yamaha/motorcycle/1972/dt2/carburetor

If the petcock isn't sealing when in the off position, the needle and seat in the carb will overflow when parked for any amount of time. That overflow can go into the engine and flood it, making it impossible to start. You can rebuild the petcock with parts if you want to keep the bike all original, or throw on one of these for less than the cost of rebuilding the original, fit has been verified by members here and it's genuine Yamaha, there are cheaper chinese knock offs but they are hit or miss for quality.
www.partzilla.com/product/yamaha/3JN-24500-02-00

Spark should be unrelated, first thing I'd do is clean the points and flywheel.

Thanks Darinm! I am going to do as you suggest. I ordered the verified works version of the petcock. I want to keep the overall look original but small stuff that can only be noticed up close isn't critical to me at this stage of ownership. I was lucky and able to find everything I replaced so far oem or nos except the rear sprocket. 

I have never cleaned or taken apart a carb but did consider it when I first got the bike. I watched a couple videos and thought it looked a bit beyond my current skills but I may have improved slightly since then. I am willing to try it and at least replacing the O-ring doesn't sound very hard. 

I like to lay out a nice clean towel on the work bench to put all the pieces on. Then just take your time, keep things oriented in the same direction as much as possible and take pictures as you go, it's much easier than you'd imagine.

I think carbs get a bad reputation from the 4 barrel ones on V8 engines, these little guys are pretty simple to take apart, clean, and reassemble.

For cleaning out the very small openings... Get a set of guitar strings.. High E..
Sneezles61

Another option, try monofilament fishing line in various weights. It is rigid enough to clear a plugged orifice but not hard enough to score, scratch or damage.