I'm running a 47.5 pilot, 170 main needle second from highest needle setting I.E. clip is second from lowest notch in 6F9 needle. 
At center needle/clip setting at cruising around 4000 and just letting off I get pinging, I used to get pinging @ 3000 just letting off the cruising throttle and richening up the pilot coupled with the air screw has fixed that. Now with the needle set high I've managed to reduce pinging at the 4000 cruising and just letting off. 
My question is this. Should I go to a 180 main and clip up/lean the middle? I am amazed at how rich this thing can run at cruising speeds, Blubbery as I've heard here lots of times and yet it doesn't foul the plug, at least not as of yet. It recovers very well from the blubbery cruising throttle position as it doesn't spit, miss and have to clean itself up when it's given more throttle. When I'm giving it full throttle it feels as though it's power drops off just under about 6000. I know this isn't a big revving engine so I'm not completely surprised by that but felt a little like that full throttle position just isn't quite spot on, a little weak feeling. 
Can I get some folks to pipe up on their carb settings on a 1976 DT400 please? I have looked through threads and the Tech library but I'm not finding sufficient information to answer this question.  

Any chance you're confusing pinging with over-rich as you back off a bit?.
You mention blubbering 'richness' so i'm sure you have the handle on both meaning--pinging & blubber.
If it goes better backing off full throttle than it does on 'full' could it be over-rich on the main & on the point of 4 stroking on full open hence slightly better backed up a bit. I dunno, i'm just woffling on.
Having my own carb issues making a 32mm work on my 360 starting from a pile of carb bits tipped on the floor lol.

Hey RT! Thanks for answering. After writing the question I went out and changed from 170 to a 180, then clip on the second from top slot. Theory was up with the main in case the slight power loss I was feeling at wot was lean (certainly wasn’t acting fat) so I figured fatter main for the wot and lean down needle to compensate for the 180 main increase. It didn’t work, really fat and was not happy at wot. Back to 170 and needle in the middle slot and I back to slight pinging. I can actually ride around the pinging, that’s how slight it is. It pulls well. Runs well, gets right up to 60-65 quickly. I’m just trying to fine tune and se just what it can really do with perfected tuning. I think you may be right that it’s a slight bit fat yet on wot main. I hoped I had a 165 but I guess there is no such animal so I may try a 160 for the fun of it tomorrow. OR…. Lol!

RT, and I did check the spark plug, brown, not tan, not white, brown so I’m sure it’s not too lean. 
I see a lot of folks running and even richer pilot, 50-52.5.
im at 47.5.

Thanks for the reply. Carburettors, yep they're a bit of a mystery & trial & error so long as error isn't too lean causing damage.
I've been experimenting with a 32mm carb called an "EI" which is all controlled by the needle & nothing else.
I only have two needles & they might be a 4 stroke taper i think.
Given up on that at the moment & bck to a Mikuni as it was inconsistant but might try it again oneday.
Think EI was a copy of a Lectron carb.
Back in the "80's a had a Blue Magnum Carb on my YZ125 which is another similar carb. Worked ok back then.

Very interesting, I'm going to look up an EI carb!!

Kenny Roberts had this to say about the previous version:

"In the mid 70's and early 80's when I raced in the USA, I did a lot of the development riding and work with the single fuel system carburetor with Red Edmonston. At the time the H.P. gain, rideability and smoothness of power delivery was superior to any carburetor we tested. I know it was an advantage over my competition.

Interesting, her is one on Ebay, brand new in the box, I wonder if one can tap the oil pump line fitting into the side of this? 
If you lookup  "EI 34mm Motorcycle Race Carburetor" in Ebay it's there. 

Ok yep i see that. Hell of a lot of money just to experiment. Assortment of needles is a 'must'.
After all my frustrating experimenting it was sort of a relief to get back to something that works as it should haha.
But i'll probably go there again sometime.