Main jet blocked so nothing can get up the needle. Maybe not. Put the needle clip on the richest as a test if main is clear. I guess you've had the emulsion tube 'needle jet' right out of the carb body as in an extreme case can build up around it. Airway to the E tube from carb mouth not blocked with crumbling air filter etc etc.

I completely disassembled the carb. Not a spec of dirt anywhere. I did not take the main nozzle out though as I didn’t want to break it.  It pulls nice in higher throttle positions though so I’m pretty sure the main jet circuit is good. 

I didn’t put the air cleaner boot on though. Could that have enough impact? It seems like it shouldn’t but thought I’d mention that. It’s such a botch to get that on with the carb and air box in place. It’s not very pliable.

Ok, i thought it wouldn't get past idle without choke but you say "pulls nice in higher throttle possitions" so needle needing richening sounds a possibility.
Or did you mean with the choke still on it will rev ok.
Does the needle jet screw out on those, not push out the top. Always good to remove them when fully cleaning the carb.
www.partzilla.com/catalog/yamaha/motorcy...78/dt175e/carburetor

Check the passages from the pilot jet through to the venturi aren't blocked .
One goes straight up , but there is another drilled on an angle exiting in front of the slide .

Both are free. I carefully cleaned them out with a jewellers drill bit set.  They were passing lots compresses air at the end.

I don't have time to read through the thread again but I believe you said you have a 1979 carb?

It's remarkable how in the same paragraph it says carb was "completely disassembled" and "main nozzle wasn't removed".    A lot of crap can hide in the main nozzle well and that can affect off-idle performance as it's an "air bleed" type nozzle.

I probably said this before but in my experience 79 carb needs at least a 25 pilot, Yamaha Banshee had 25 stock if you can't figure out how to order the right type from a Mikuni distributor.

Air screw ineffective points to carb not as clean as described or possibly an air leak...  Kind of confused on that too though as if choke (enrichener) was on, air screw might not have any effect at all. 

I probably said this before as well...  ignition side main seal is prone to vacuum leaks on that model as is the reed manifold "gasket" joints on all models.  I always pressure/vacuum test first to ID any issues with air leaks but most people just replace carbs, seals, etc until hopefully the problem goes away. 

Sorry I should have been more clear on completely disassemble. Everything came out and was cleaned except the main nozzle as it seems a press fit.  I did not want to damage it or the carb body as they both seem made of unobtainium.   I don’t think the main circuit is the issue as the bike revs up nice  it just doesn’t want to idle. I’ve now put the carb to air filter boot back on so will try it like that. Hoping the extra resistance will pull more fuel through the pilot.   I’ll post up when I get days off again.   Also need a OEM fuel cock. The junk Chinese unit I got off of Amazon was so poorly made it leaked immediately. I’m only out $15 there so no big whoop. I knew better…