1974 DT250A No Spark. Here's what I've done so far:
-New Points gapped at .3mm,
-New condenser, Measures .2microfarad in ckt. meter accuracy suspect SB .3microfarads
-New spark plug.
-When I shock the ignition coil I get spark on the plug. (momentarily hit it with 12vdc. ).
-Wiring traced out good with no grounds.
-Ignition coil swapped without changing results.
-AC measured from the black lead coming from the points was 1.8 VAC when spinning engine with a drill. (I
have no idea what this should be but that should be an indication that the coil is putting out something at
least)
-Lighting coil was changed because of physical damage, but that shouldn't have anything to do with spark,
should it?
Source coils don't appear to be available from any of the sources I normally use. Any ideas? I don't believe a battery is required, is it?.

Does it look something like this. There's only one black wire heading out of the mag to run the coil up top--via the loom & switch of course but could shortcut all that & go direct to the top coil from the mag. In the pic i fount the green goes around to the points & had me thinking where's that think its going, but can see it when expanded up. So can see source coil earthed on the end, then other over to condense, then green around to points, then single black heading out up top to coil. If you had the source coil in your hand then should be no resistance to earth/coil pole, but guessing about 1.5 ohms measured between each end wire, not much ohms resistance but its not an exact science either.

1st thing is try another plug,
I just went through 2 new plugs and yes both were fresh out of the box, first one was new and showed arc but was bad !

This is good advice. I put 2 new NGK's in my CB175 a while back and it was running on 1 cylinder right away...replaced it with one of the old ones and off I went. Over the years, I think I'm up to 3 brand new plugs that didn't work out of the box now. I also had one that lasted about 50 miles on my DT3. And make sure your plug cap is good. They are inexpensive and easy to replace. Go ride your bike!

It would be interesting to know where these non functioning plugs were purchased from - eg online, local dealer etc. Are you folks returning them to the vendor if they aren't working properly?

I think there was a thread on this forum a while back about counterfeit plugs being produced and sold as genuine.

Straight from the horses mouth so to speak

www.ngk-sparkplugs.jp/english/techinfo/fake/index.html

Yes, that's the article I remember reading. Well found!

It does, but the source coil is a bit smaller.

I tried 2. They both spark when I hit the ignition coil with either 12v or 6v. I've had plugs that spark in the air, but under compression won't work, but these plugs appear to be fine.

Some models combine/connect the lighting and ignition source coils.

(Question I have is who and why replaced lighting coil... was it running before and after replacement?)

Second is you've mentioned "gapping points" Nothing about timing. Unfortunately on some 250s' the backing plate is slotted and and it's possible to move the plate and screw up the timing of when the ignition energy produced and when the points open. Energy needs to be at or very near max when points open.

Or using poorly made points can cause the same issue.

If timing is set correctly, and then points are within gap range given in manual you should be okay. (you don't really gap the points on these bikes... you set the timing with the point gap and then the point gap should be within spec... if you have quality OEM points) Best thing is to never mess with the stator position even though slots allow you to... mark it and put it back where it was stock.

And common issue I've seen... especially when something has been "rewired" or replaced... is that the wire rubs on something or the insulation is damaged.... sometimes it's a tiny break in insulation and almost impossible to see.