New Hotter Coil for Points Ignition

[jopower]

I've got a 78 XS650SE with points and dual coils. One coil primary shows 2.1 ohms (half spec) so it's weak on that cylinder. I've considered an electronic swap from my 83 parts bike but there seems to be a problem with that system (and may be why it doesn't run). For now I just want hotter coils. The preference would be a pair of hot new coils that fit near the stock locations. But...

I happen to have a stock Harley electronic igniton coil (#31614-83a) with the same connections as the the Yamaha electronic (2 x 12 volt primary wires, 2 x hi-volt plug connects). The primary resistance is ~2.5 ohms (I still need to see if that is good for a Harley coil). It looks like a fair fit in place of the old coils with some artistic wire routing. Note: 78 Yamaha stock coils spec 3.9 ohms (10% variance).

I know the new coil should be firing ~25-30kv (up from ~15kv) with points and condensors but 1960's cars did that all the time: V8's fire 4 times a rev for 20,000 sparks a minute at 5000 rpm. I'll be firing 1 per rev (split to 2 plugs simultainiously) for a max of 7500 sparks per minute. So that looks good.

OK... will this work or will I be torching points? Do I need to make a different set of condensors (say 2 Bluestreaks for a 60's Chevy?) to make it work?

[jopower]

Have questioned several local shops and the word is you can't use very many electronic igniton coils with points. Either they won't work at all or the resistances will torch the points.

Here's what the mechanics said:
The simple tests are (1) to have an OHM meter connected to a primary lead and the spark tower (all leads to coil disconnected). Do you get a reading below 20k OHMs at all? If yes, (2) can you also get a high (8-15k OHM) reading from the spark tower to any location on the outside of the coil? Mounting lugs are a prefered contact. If both of these come up, you've got a good chance of a coil swap working.

The tough part is getting a good match with the Yamaha electrics, esp the points and condensors. So far all the local mechs said that the best bet is to use a Harley points coil. All are rated above 25 kv and the price is reasonable ($40-50). Do we need to change condensors? They all said "maybe". Only one offered an opinion beyond that. He suggested that high quality Blue Streak condensors should be able to stand up to cycle use and to try those for a 60's V8. Strange none said to use Harley condensors.

You should expect that hotter coils will OHM test somewhat higher on the primary curcuit as the path is longer due to more windings. Our 650's coil primary spec is 3.9 OHMs (5% var). I note most OEM 25-30 kv automotive points coils spec 8-12 OHMs here.

Has anyone used these or other hot points coils? Like to get your impressions here.

[jax650]

I used 2 Dyna "green" coils for points ignitions with new condensers from a tune-up kit for xs650's. I think primary resistance was about 3 ohms. Tank clearancing needed under the tunnel area accomplished with a large ball-peen hammer and only a few swings got plenty of clearance! Don't let them rub or coils will eventually wear through outer case and short to ground against the tank! Iridium plugs and these coils allow me to run .035 plug gap with no issues ever. Wider gap gives larger spark and easier starting, at least in theory, I didn't have any starting issues before though........YMMV