Looking for a lesson in outboard Points and coil theory

[newhamburgboating]

I have a 69 Johnson Electric Start, troubleshooting a no spark issue.

I am wondering if someone can explain how the points work to me, I have been doing some continuity tests with my multimeter and am rather confused. I would like to know if what i found is normal, or the cause of my issues.

When i have on of the points open by rotating the crankshaft, i connect my multimeter in the Ohm setting to each side of the points. I would expect this to be a reading of 1ohm, (no conduction). yet i get a reading of 0000, meaning with open points, they are essentially connected anyways.

the bracket for the points is obviously connected to the amerture plate below, and the stopper piece that sticks up to catch the spring on the point, and give it it's open close ability is part of the bracket that is grounded, therefor the spring is connecting each side of the point to the grounded bracket that holds it all together.

Again, what i would assume is, points open = no conduction, points closed = conduction = spark!

however i always have conduction. did i miss some little piece of insulation, say on the post that catches the spring, or perhaps the entire underside of the point bracket should be on an insulator?

HELP !

 

[Chris1956]

Re: Looking for a lesson in outboard Points and coil theory

Well, I looked up a '69 Evinrude 85HP motor as an example. It has two sets of points and an ignition amplifier. It is therefore not a conventional points/coil ign. On a lot of those Evinrudes, the points work together. Both must be open to fire the spark plug.

In general, the ign coil is charged by the stator, when the points are closed. Closing the points competes the circuit. Now as the motor rotates, one set of points opens, followed by the second set of points. When the second set opens, the charge in the primary coil collapses as the circuit opens. This induces a high voltage (> 20K volts) in the secondary coil, firing the plug.

 

[newhamburgboating]

Re: Looking for a lesson in outboard Points and coil theory

thanks for the reply Chris,

that's certainly an interesting twist on what i was thinking, however, I have had this whole thing apart now and do not believe i have a Stator, below is a couple pictures, one is from the manual, the other, well, my motor.


Does the lack of a stator mean the points should or should not conduct when open? just having a hard time wrapping my brain around this one.

 

[gm280]

Re: Looking for a lesson in outboard Points and coil theory

Contrary to what a lot of folks think, the points opening cause the spark, NOT the points closing. When the points are closed the voltage builds up in the primary side of the spark coil through the points to a saturation condition. And as the ramp lobe on the crankshaft opens the points that primary field in the spark coil(s) collapses and that creates a secondary outputs as a high voltage pulse to the spark plug. The amount of time the points are closed is called the "Dwell time". The capacitors (condensers) are there to help keep the points from arching as they open. So you either have an exciter coil, or are running from a battery. There is no other way to create a spark without some type of voltage… I hope this helps you understand how points work...

 

[Don Hansen]

Re: Looking for a lesson in outboard Points and coil theory

Edited I did it again.

Set your meter to a lower scale. When the points are open you are reading the resistance of the windings of the primary side of the coil. It will not be very high but there will some value. When the points are closed you should get 0 ohms. It's when the points open that the spark plug fires. If your interested, try doing a search on "How a magneto works".

DLH

 

[nwcove]

Re: Looking for a lesson in outboard Points and coil theory

to keep it as simple as possible, think of the points as a valve, and think of the coils as a pump. when the valves (points) are closed, pressure builds ( electrical), as soon as the valves ( points) open, the pressure is released.

 

[newhamburgboating]

Re: Looking for a lesson in outboard Points and coil theory

Thanks everyone, backwards of what I thought but certainly makes sense now that its explained.

Love this forum!

 

[roscoe]

Re: Looking for a lesson in outboard Points and coil theory

Thanks everyone, backwards of what I thought but certainly makes sense now that its explained.

Love this forum!

Well, you would have been right, if you had a points/maker ignition.
But you have a points/breaker ignition.