1975 Yamaha DT100, no spark, previous owner replaced plug, points, ignition coil, still no spark. I purchased bike, he said could be a bad source coil. I've done a good physical inspection, the source coil does read 1.8 ohms, the Clymer book says should be approximately .5 ohms, should I spend 50 bucks to replace the coil or spend 120 to upgrade to CDI ??? Any advice would be appreciated.

Original main components are sturdy, most often issues are related to dirty point contacts (even new points), poor soldered connections at the new condenser (solder is touching the condenser case)...things like this. It's pretty rare that the actual problem with a points ignition is a bad component...unless heavy hands have been in the stator area before and jacked up fine connection points for the stator coils.

If it were me I would vet the wiring from the coil to the stator, bypass ignition switch (if it's there), single wire from the coil to the points. Clean the points. Clean the coil ground to the frame (no paint between the two). New plug...start basics, as MOST of the time the hard parts are OK.

DT100 shop manual here:

yamaha-enduros.com/index.php/workshop/se...-125-175-full-manual

I've also seen point/condenser wires poorly routed and insulation rubbed through... can be hard to spot sometimes.

Thanks all for a speedy response, Happy Thanksgiving to all, will pick up the project tomorrow.

Thanks for the PDF file of the owners manual, the source coil checked good, condenser also checked good, points cleaned and adjusted. Unwrapped and inspected wiring harness no defects seen, ignition switch checked good. The ignition coil I ordered from Amazon ohms the same as the coil on the bike when I bought it .7 ohms on the primary and 2.6k ohms on the secondary, this is way off of what the manual says, 1 ohm and 6k ohm, could this be my problem??? and how do I get one with the correct values ???

Great news, I ordered and received an old stock Yamaha ignition coil, bike started first kick. I am now a believer of original parts, bike had 2 coils changed before I got the correct part.