Correction: Now I know It MIGHT? be worth it to replace the old coil with the pricey new/old 131.6 ohm already +/- 9% out of spec going the wrong way coil

I wouldn't worry about the small numbers out of spec but large amounts could indicate internal shorting between the windings .

Hi all
    Update to the replacing the old 96.6 ohm charge coil with the new-old stock 131.6 ohm charge coil. IT WORKED!!! Great Blue Spark!!! I spent most of the day riding it around the neighborhood illegally of course. It was like meeting up with an old lost friend. This was the problem that sent it to the back of the garage since around 1980.
    Anyways next step is an appointment to the California Department of Vehicles. Let The Night Mare Begin. Have the pink and old 1982 Registration. It wouldn't surprise me if they try to charge me late penalties for the last 40 years. Also going to try for vintage vehicle status. If anybody has any help on that, it will be appreciated. Thanks again to Buggin and  Brett  for the right ohm stats on the coil ohm info.
 

That's great news. Thanks for posting an update. I bet that is the same issue that mine is having. Wish I had another CDI coil to test with. Good luck with registration I also have a similar nightmare with my DT400. I have no title and someone wiped out the VIN numbers long ago, playing phone tag with the local police hoping I can still save it from being junked.

Yay, everyone's sorted--i think. Good results all around.

I think I have the same issue.  Where did you get that part?

 

Hey SaudeDT400
     I bought the coil on ebay, " New Old Stock". Its an 6 volt A/C coil that powers the ignition (CDI) headlight and speedo-tach lights. I think I paid about $130 for it but I found a shop that builds them new for about the same price in the UK. I will get back to you this weekend with more details. Have you check the ohms value on the coil? The shop manual is wrong at 120 ohms. It should read about 131.6 for they weak-in with age. It makes a difference. Also check to see if you have a spark on the spark plug. It should be a blue spark with a .020-0.24 gap. Don't buy a old 45 year old used coil.

I bought a 74 DT360 that "had no spark"....I measured a bunch of resistance values and then decided to spray all the connectors down real good with contact cleaner and she started right up. Apparently a bit of extra resistance was all it took to not spark.. Just a stupid idea, but maybe you get lucky like I did.

Hey SaudeDT400
   This web site   Yamaha DT, RT, DT250, DT360, DT400 CDI Ignition-12v/180W, 7238799DC - HVCcycle   is a really good starting place to go for info on ignition systems and parts. The coil that fits your bike is around $65 without shipping. If you email them with questions they will get back to you. I would have bought from this site if I didn't by from ebay first. Hope this helps.