1971 DT250Bike is hard to start, have to open throttle to full to get it to start with the choke on.  It is not flooding.  Once started it pops and spits but smooths out in about thirty seconds of revving.  It runs and aides great, very strong but when I take it on the road around fifty to fifty five  mph in fifth gear with half to 3/4 throttle I hear what sounds like pinging.  The ping goes away with acceleration or deceleration but comes back when holding steady throttle. Don't know if it is related but it also stops running when I turn the lights on. The bike started better before I did the following but was still pinging.  Thoughts ?new piston and rings .25 overnew left side crank sealrebuilt oil pumprebuilt carburetor stock settingsnew plug BR8ES gapped at .018 gapnew points and condenser .012 gapcleaned exhaust pipe by cooking it out 

I experienced similar performance with that plug in a '73 DT3. the "R" indicates resistor plug. I put the standard non resistor plug B8ES in and it started and ran normal.

If you order B8ES from some vendors you will get the BR8ES.

Others have had good performance with the equivalent Autolite plug.

Do a bubble test on the left seal with the spark plug tight.
If you have bubbles kick starting the bike with soapy water, get another one in there..

a

I switched to Autolite # 4054 = B8ES no problems with the Autolite 

Bit difficult to guess & depends what you call pinging which i relate to detonating but i'm guessing it's not that with points at 12 thou so theoreticaly fractionaly retarded compared to 3.2btdc. Regardless i'd open the plug to 20-22 & points to 15-, nipping 15 & then decide if you might be desribing richness blubbering on the needle. I think that because you say it doesn't do it if you open throttle a little more or roll it back under that point. If 'that' try raising the needle clip one notch at a time. I guess ya trying to be carefull after reboring understandably. Carb little Oring is critical but wouldn't rev at all if it's badly leaking letting fuel up the spout & bypassing the main jet.
Starting again i see you say needs full throttle with choke on which isn't good. Makes me think it 'is' flooding up. Try it from cold with no choke for a test. Starting to rethink the small Oring theory now.
One more poke. Restricted or blocked pilot jet can aid pinging as in detonating when rolling the throttle back on a hot motor. Probably more likely on a 360 as pretty temperamental with carburation. I had a guy come to me with a KX500 years ago & pinged & carried on but idled very lean, not realy wanting to run on constant low throttle. & was a blocked pilot jet. Long time ago & might've been the hole or both holes angled & straight up from the piolt out into the venturi that had something blocking it. Sort of one of those jobs you'll never see twice. Man was an arm stretcher down the paddock lol. Could get severely injured on one of those!!.

Thanks, I will try this for sure. 

Thank you very much, you gave me a lot to consider and it makes sense.  One thing I have noticed about this forum is that just having some support thinking through or validating your thoughts is helpful to keep on track.

I changed to the auto lite and it did improve the way it ran but she still pings a bit

Well, I spent some time changing g plugs and the carb needle.  While it ran a bit better it still pinged.  I took off the flywheel just to check the points etc and found that I must have bent the points when I replaced the flywheel.  After I straightened it out and set the points to .14 it ran much better.  However the darn ping still audible at steady 3/4 throttle in fifth gear.  I am going to run some premium to see if that helps.  Funny thing is that the plug is now a nice gray.  Maybe it is not pinging ?

Plug should be a dark brown, maybe I'm wrong but I say you're still running lean.