Hello strokers
I just want to pass this by the forum to hear what you guys think.  My DT125 1978 has a Mikuni MIC 2NO carb
I keep forgetting to note down what the jets are (but assuming they are standard)

the PO has set
- the needle to the middle setting 
- idle screw to 1 3/4 turns out from stop
- pilot air screw 1 full turn out from stop
- and was running an NGK B7ES 

and it seems to me that the set up was probably running well (but as the PO didnt have any history on the machine, it is possible someone switched the plug out etc etc, but the machine shows minimal signs of being messed around with)

so I am thinking of staying with these settings, what do you guys think, and are there things I should look out for and listen out for.  Thanks for your help

 

Most of the questions you're asking are a little like me posting this picture and asking if I have it in the right place.

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It's not that there's anything wrong with asking...  as long as you realize the difficulty of anyone giving you a good answer, or answering at all. 
What complicates this even more is as far as I can tell, most of the world got the "2A6" model.  I haven't ever seen carb specs for a 2NO...  but they could be identical to the 2A6?  Someone could tell you that if you listed the sizes of all the jets in your carb...  or you might even find a "2A6" stamped on the side of the carb near the starter plunger.

In the US, Yamaha specified a Champion N7 plug in 78-79...  when they went back to NGK, they specified a B8ES, which is what the current Yamaha parts lists show.  I can't be 100% certain but my guess is a B8ES would be the correct plug? 

MARKT, you are absolutely right. I also felt that the B8ES is the correct plug but dont know enough about what people are doing over here with these bikes. It just appears to me that the PO rode the bike for Enduro and rode it well - and there are almost no mods except the plug. The carb here is stamped 2NO but I am suspecting its pretty similar to your NA 2A6 but don't know about any market changes between NA Canada Eu or Asia. I just thought maybe others might have been running this plug with good results, and being new to this bike didnt want to shoot off and do something very nasty to the engine - I respect your reply, I think I am just going to have to 'feel' my way forward. Currently the carb is running lean, but this can be so many issues, especially with the tank still being a bit gunky and the carb still not super clean and air leaks coming from here and there.
Thanks again for helping me on my way.

Ignition side crank seal is prone to vacuum leaks on that model in my experience... I use the better seal from the 77-79 IT175