Theory of Ignition Operation

[turtle1173]

Hi all,<br /><br /> First of all, please excuse (temporarily) my ignorance in this matter. I have only owned and operated Chryslers but am anticipating a Johnson/Evinrude purchase soon.<br /><br /> I am very familiar with the ignition systems of Chrysler outboards but I wonder how they differ from Evinrudes? I was recently looking at a 1975 70HP Evinrude and I noticed 3 odd looking coils (compared to what I'm used too) on the right side of the motor. Can someone briefly explain how the ignition system works? Also, how does it differ in a V4? How has the ignition system changed over the years (say, from late '60s through the '80s)?<br /><br />Thanks and I hope I didn't ask too much.<br /><br />Shane

 

[Hooty]

Re: Theory of Ignition Operation

The flywheel and stator is/are a magneto. They generate voltage which is stored in capacitors (three in your engine) in the powerpack. When it's time for a cylinder to fire, the stored voltage is discharged to a coil (one of the three you mentioned) and that steps the voltage up to firing voltage which goes to the sparkplug and lights off the fuel/air charge in that cylinder. <br />The factory manual does a lot better job of explaining then I do.<br /><br />c/6<br />Hooty

 

[turtle1173]

Re: Theory of Ignition Operation

Thanks for the info.<br /><br /> Is there a trigger assembly under the flywheel? How reliable were these ignition systems? What kind of changes have been made over the years?<br /><br /> That sounds similiar to some of the later Chrysler ignition systems. But the Chryslers (Type III Presolite) were pretty unreliable.<br /><br />Shane

 

[OBJ]

Re: Theory of Ignition Operation

Turtle, on the particular engine yur lookin at, there is a timer base under the flywheel. The timer base has three coils in it that generate a voltage, at the right time, to fire the power pack for a particular cylinder. The voltage is generated from a magnet in the flywheel when it passes the coil. This system is used extensively on Johnny/Rudes and is a very reliable system.

 

[turtle1173]

Re: Theory of Ignition Operation

Thanks for the replies.<br /><br /> Does the ignition differ on a V4? How about the 2 cylinders (like a 50HP)?<br /><br /> I know this may be out of place on this forum but does Mercury use a similar ignition design or is it completely different?<br /><br />Thanks again,<br /><br />Shane

 

[OBJ]

Re: Theory of Ignition Operation

Turtle....the same type set up applies for just about all Johnny/Rudes after 1980....maybe earlier. Merc has about the same set up.