My book says my coil resistance should be 4.0 Ohms (+/- 10%) on the primary and 9.5K on the secondary (+/- 20%). Unfortunately, I get 2.9 and 2.7 Ohms (more than 25% off) and 20K to 18K (like 100% off). Any time I use the electric starter on a cold, choked engine, my plugs like to foul. I suspect it's because the starter draws all the juice and there's none left over for my weak ignition system.
However, I think the book might have the wrong specs for my bike's coils. The Haynes covers Yam XS400s from '75 to '84, but only really details the early models with points ignition -- only passing mention is made of the later electronic ignition (which I have) in the last section of the book. The picture of the coils in the book is also way different from what's on my bike. Could the electronic use different coils? Are my Ohm readings so far off that I should consider replacing the coils?
'07 Ninja 500R, formerly '81 Yamaha XS400