Author Topic: Coil Question  (Read 513 times)

Offline Scout63

  • Gaggle Hero
  • *****
  • *
  • *
  • *
  • *
  • *
  • Posts: 2682
  • Location: Orleans, MA USA
Coil Question
« on: January 14, 2022, 10:27:23 PM »
I’ve been trying to set the points on my new to me ‘79 1000SP with factory wiring and coils.  The right side points adjusted fine, but the left side were showing continuity to ground even when open.  They would only show no continuity when both the left and right points were open.  After chasing down all of the wiring I found that the right points when closed were grounding through the trigger wire to the right coil, which was then grounding back to the left points through the left trigger wire.  I guessing this was through the power jumper wire between the coils.

I’m guessing also that there shouldn’t be continuity in the coils between the trigger spade and the power spade.   I wired a diode into the right trigger wire near the coil to allow the trigger voltage from the right points to the right coil, but not allow continuity the other way. Now the points test fine with the ohm meter.

Is this just treating the symptom?  Is it possible that insulation between the coil spades is defective? Wouldn’t this situation only be possible if both coils permit continuity between the spades?  I’ve checked all other possible ground paths and found none.

I could just buy a Dyna III but since I’m probably going to flip the bike I’d like to keep the expenses down a little.  Also I’m determined to get better with points. Usually I install EI and punt on learning this.

Thanks everyone. Here’s the wiring diagram - credit to Greg Bender.


Ben Zehnder - Orleans, MA USA

Offline Kiwi_Roy

  • Gaggle Hero
  • *****
  • Posts: 9796
  • Location: New Westminster BC
Re: Coil Question
« Reply #1 on: January 15, 2022, 03:13:16 AM »
That looks normal, the problem is you must be using an Ohmmeter or high impedance meter.
You need to put the battery onto the common wire between coils.
Use a timing light or any low wattage 12 Volt lamp from the points end of the coil to chassis.
Now you will find the 12 Volts goes through the coil to the timing light to chassis or direct to chassis if the points are closed.
 

----------------------------------------------
I showed the condensers as they are on the coil side of the points.
You don't need two timing lights as I show just set one set of points then move it over to the other coil.
The coils will get quite hot if you leave them on for any length of tome with the points closed.
« Last Edit: January 15, 2022, 03:49:19 AM by Kiwi_Roy »
72 Eldorado
17 V7iii Special
76 Convert
Half a V9 Roamer

Moto Guzzi - making electricians out of riders since March 15 1921

Offline Scout63

  • Gaggle Hero
  • *****
  • *
  • *
  • *
  • *
  • *
  • Posts: 2682
  • Location: Orleans, MA USA
Re: Coil Question
« Reply #2 on: January 15, 2022, 07:06:43 AM »
I was using an ohmmeter Roy.  That makes sense.  I’ll try it with a timing light. I wired the diode in with spade fittings at both ends so I can just remove it. Thanks. Ben
Ben Zehnder - Orleans, MA USA

Offline Kiwi_Roy

  • Gaggle Hero
  • *****
  • Posts: 9796
  • Location: New Westminster BC
Re: Coil Question
« Reply #3 on: January 15, 2022, 11:56:46 AM »
You could use the Voltmeter to measure Voltage relative to chassis at the two points I show a lamp, it would change from 0 to 12 Volts when the points open.
The reason Ohms doesn't work, each coil is maybe 4 Ohms so effectively you only have a maximum of 8 Ohms at any point, the Ohmmeter would always show ~ zero,
--
Any 12 Volt lamp is more visual, I use an old tail light bulb with a couple of wires with alligator clips attached.
« Last Edit: January 15, 2022, 11:58:03 AM by Kiwi_Roy »
72 Eldorado
17 V7iii Special
76 Convert
Half a V9 Roamer

Moto Guzzi - making electricians out of riders since March 15 1921

Wildguzzi.com

Re: Coil Question
« Reply #3 on: January 15, 2022, 11:56:46 AM »

 

***Wildguzzi Official Logo High Quality 5 Color Window Decals Back In Stock***
Shipping in USA Only. Awesome quality. Back by popular demand. All proceeds go back into the forum.
http://www.wildguzzi.com/Products/products.htm
Advertise Here