My DT175B runs rich, I have found that when I remove the pilot air screw it no longer runs as rich.  I have down sized the pilot jet from a #25 to a #20 and with this smaller jet in and the pilot air screw out it just barley runs rich.  Basically only at 1/8 throttle.  Does this mean that the idle air circuit is stopped up?  Or is there another circuit possibly restricted?  Or does it even matter knowing the carb needs cleaned

Jet setter o-ring leaking or missing.  (seals to float bowl).   Part #3

www.partzilla.com/catalog/yamaha/motorcy...75/dt175b/carburetor

So I checked jet setter O-ring and it is fine. I then cleaned the carburetor again. This time I soaked it for 40 hrs., rinsed thoroughly and this time blew out all of the air circuits in the carb with carb cleaner and compressed air now that I have an air tank. When I put it back together and tested it it is now running properly no longer running rich. Evidently the pilot air circuit was partially/totally restricted.

could someone possibly give me their opinion on what this thing is doing?  No matter what I do it still does this.  Sometimes it will run a little longer but not more than 15 seconds longer.  The only thing that I can do to make it die faster is open the choke.  It does this with the exhaust off and in this video the air box is disconnected.  I have tried float level from 19 to 23, new o-ring, air screw any where from 1/2 turn out to all the way out, needle in 1st thru 3rd position 2.0 and 2.5 slide, a 20 - 22.5 and 25 pilot jet main jet from 150, 160 and 170. Nothing will make a difference.  And I did pressure test for air leaks not finding any.. So it was running real good just a little rich of idle (maybe 1/8 throttle) then I adjusted the needle to position 2 and this not running happened and I haven't been able to correct it since. I also tried another carburetor with stock setting and it did the same thing.  so makes me think it is not fuel but honestly as you have already figured out I have no clue.

imgur.com/a/ONPbbAd

did you put the c - clip back on the needle?  you said it was running and this was all you did. 

Watching the video you have an electrical issue. 
First check the points gap isn't going out past 14-ish.
Then check plug gap & set at 20 thou.
If that doesn't fix it I'll eat my hat. Have lots of hats but the piles getting smaller as often wrong lol.
Might be a primary source coil issue but do the main things first.
With the source earthing into the centre of the lighting coils & if you turn the lights on with dirty points or too wide in the gap, it will play up big time misfiring & worse if plug gap is wide.

unfortunately i did.

Just going to put this out there.

My 74 DT125 had a pretty good on /off firing and couldn't figure it out for a while. acted like a bad coil...because it was, kind of. In my case, the primary coil wire connection was 100% loose in the bullet connector and touching each other lightly, but not 100% of the time. So it would mostly fire. Reminds me a bit of yours.

I wonder if you used carb spray when it starts missing to see if it just needs something to burn for fuel.

Have you tried riding it?  It might just be "loaded up".