I can close this out as RESOLVED!!!!

I bought new Yamaha parts $$$ as listed below and it runs perfectly now.
As a matter of fact, it’s pretty scary now for an old man like me. 

New throttle valve (slide), needle & nozzle (emulsion tube), and needle valve assembly.

Sure glad it worked because I spent almost twice what I paid for the bike.
lol i paid $100 dollars for the bike before I fixed it up.
imgur.com/a/v79FTVW


 

So glad its resolved. looks great too.

Oh my goodness…..
I just went for ride on the backroads and amazingly enough these new carb parts also cured the dreaded issue that I had come to accept after reading how so many other DT400B owners had the same issue.

It no longer stutters or stammers when it plains off at cruising speed like 45 or 50 MPH. It now just purrs like a kitten throughout the entire range of throttle. I’m going to replace these equivalent parts on my DT250B that has recently started misbehaving in similar fashion.

Was the slide you replaced have the stock cutaway , or did you try a different option .

Good point 'that' Swoop.

Right, Schu, i discovered the same, as written in the "Shunting" thread
New Carb parts, in my case needle and needle jet (emulsion tube), and i had a different bike withoout issues.
Now going to improve my 250B, i think, also here to expect an improvement.
 

It is the same stock 3.0 cutaway. I replaced a few parts all at the same time, so it is hard to know if it was one part in particular or if they were all worn and all part of the problem. My guess is that Morley was probably on the mark when he commented that the big bore bikes seem to be hard on the needle and emulsion tube. I already ordered the same parts from DEET for my 250, less the slide which still looks like new.