Hi again everyone! It seems that just as I have gotten my bike running, more bad luck has befallen me. I was out riding on a road when something odd happened. I came to a stop (may have revved engine, can't remember) and the headlight went out. I noticed that at the same time, the bike (which had been running quite well prior to that) began to run terribly, with lots of sputtering, some semi-backfires, lots of smoke, et cetera. My friend and I soon thereafter realized that the tail light had also stopped working. It was then that the tail light fell off and shattered. Awesome.

So fast forward to now and what I currently know: Turn signals and horn are working normally, headlight does not work (high or low beams). I have used a multimeter to check for voltage on the tail light leads and see nothing. I plan to do the same with the headlight, although I will have to take it off to do so. The bike has no battery in it at the moment, nor did it while it was working before. I seem to recall someone saying that lighting components could influence how the bike ran, so I am thinking that's related to why it started running badly. I also ordered a new tail light for $40 total on ebay, not so bad if you ask me. There is no rear bulb to check, and I might take apart the headlight and check the bulbs to see if they're blown or not. Let me know if this stuff is worth doing or not.

One possibility is related to one of the lighting coils. If you haven't read the conclusion to my novel of a first post, I was having an issue with an old brittle wire coming off of one lighting coil which I managed to connect reasonably well, but not perfectly, back to the source coil. I was thinking maybe this coil has disconnected again, but then again the last time that supposedly happened the bike wouldn't run at all. I am hoping this isn't my issue because I dread having to take the flywheel off again and also re-timing the points, but if you think that might be it then that's what we'll do. 

Thanks again for the continued advice and support! I'm trying not to let this get to me, I've had about two days of riding this thing without issues so far and I'd like to increase that number if possible. 

Also, here's a quick video of me running the bike to illustrate how it's performing. There's a low band where it's fine and then a high band where it's pretty much fine but between those two there's a certain RPM range where it runs horribly and makes odd noises (backfires? its like a "choof" sound). In the video, I start with the throttle twisted a little bit, then twist and hold it in the "problem range," then twist it a little more until it makes it into the higher okay-ish range. I then take it to idle, put it in the sputtery range for half a second, and then rev to the higher speed. I was trying to show the exhaust pipe to see if you could see the sputters. Let me know if anyone knows what this sounds like or if it could have been caused by the lighting issue.

photos.app.goo.gl/7TLmRvCPjpCTLHiJA

Additional update- I have checked the bike with a multimeter and despite seemingly getting nothing last night (I may have just done it wrong) I am now reading 12 volts at the tail light for both the brake light and the static light. I am also getting 1.5v at idle on the headlight, increasing to around 3 when I rev it. I tried the headlight with a 6v motorcycle battery (separate from the one for the bike) and it won't light up with 6v DC. Resistance tester also reads overload between all terminals, so it's looking like the bulb is potentially blown. Gonna have to look for a replacement.

Current operating hypothesis (and hope) is that MAYBE some kind of power surge blew the headlight and tail light at the same time. The change in the inductive load on the system caused it to start running differently. Hopefully if I get a new tail light maybe things will go back to normal? Any and all input is appreciated, I hate to see it run this way and have zero idea what could be causing it. Thanks again!

With no battery you'll be lucky to "Not" blow the bulbs--which it sounds like you now have. If the blinkers have survived they are likely getting power from a lower output charging wire but i'm guessing they aren't operating in the usual DC regular flashing mode & brightness & flashing intervals alters with revs. Brake light would run from 'that' too, so if brake applied the blinkers would stop. I'm guessing a whole lot here so can [will] be corrected. Need a battery or if ya don't wat to run one then fit a refulator to the yellow. Or fit it to the blue then it gets everywhere . Sorry i skipped through your story & might be off the case.
Also--if i caught the story right--missfiring--the lighting & ignition source coils are linked. So if one or other is loose or shorting in the windings then it'll affect the ignition. & ignition points gap if set too wide will cause missfiring when lights are on. Ok enough info for now incase i'm sending you in the wrong direction.

Just listened to the Video & what i said in the last sentense applies. Not only points gap but spark plug gap too. 20-22 for the plug & no more. 12-14 for the points & must be clean. Ok i'm not thinking timing 'but'!!. Up from 15thou & more than likely over advanced from 3.2btdc. 12-14 & you'll be safe.

19STUBERD you ever find out what the issue was? My 1972 DT2 250 is making the same backfiring and decompression noise as your was in the video.

Thanks!