The 1974 DT250A
Had CDI ignition. It was the first year of the "NEW" Yamaha enduro, which incorporated the MX frame from the previous years motocross bikes, along with a through-the-frame exhaust system, lower CG, thermal flow shocks, etc.
If the bike is drooling black crud out of the exhaust flange, the lower end is full of crudded up gas/oil from sitting for a long time, Also, the crank seal on the primary drive side could be blown, and is sucking in tranny oil, causing the black goo.
And no, the headlight doesn't have to work for the bike to run. If you have "no spark" the best bet would be to buy a Clymer manual, and find a donor bike at a salvage yard, to pirate igniton parts off of. The '74 wasn't as easy to work on as the REAL Yamaha Enduro of '73 (that had a magneto/points igniton).
Contact Speed & Sport Yamaha in Bloomsberg PA for all the NOS parts you want. Tell Cindy I sent 'ya.