Omc 2.3 coil testing

[Hambone83]

So I have an Omc 2.3. I installed a new coil last year and soon after I was having an issue where after I ran for 20min or more when I shut the boat down it wouldn't start again till if cooled down. Since coil was the only thing I changed I was thinking its probably the problem. I read the coil should have 12v with the points closed an 9v with them open. Can I test this with the cap off and opening the points by hand? When I did that I had 12v either way. Also do I test voltage from the positive side of the coil to a ground or across the coil? Across the coil I get nothing. Also all my testing was done with the key in the on position. Not the start. The coil i put on was what napa had crossed over the sierra 18-5433 to. It has no writing on it saying if its internal or externally resisted. unfortunately the old coil is gone. From what i've read it should have an externally resisted coil but from my tests it seams like i should have an internally resisted coil. Any help would be greatly appreciated.

 

[bruceb58]

It should have 12V with points oven and 9V with points closed. You can manually open the points yourself with the cap off. If it's always 12V, you are missing a ballast resistor or resistor wire leading to the coil or someone wired it so it's 12V straight to the coil.

It should have an external resistor coil.

 

[Hambone83]

Thank you for the Info. My wiring is all original and i believe it has a resistor wire "purple with red'.coming from the alternator. Could that wire somehow be alowing 12v through instead of 9? Doesn't seem possible since i believe they create the resistance with the size of wire. I am probably wrong though. Could i just leave it and put and internally resisted coil on it?

 

[vinnie1234]

points ignition systems have a ballast resistor. it 's purpose is to allow more or less electricity to the coil as rpm changes, since the time period in which the points are closed decreases with increased engine rpm. If I remember right you should be able to measure either 1.2 or 1.4 ohms across this resistor cold to verify it's condition. I think it's 1.4 ohms.
in either case, I don't think it would cause a no start if it was bad.
If it starts again cold, perhaps you have a fuel/carb problem. What do your spark plugs look like after shut down?

 

[bruceb58]

The coil is designed to run at a lower voltage than battery voltage. That's why the resistor is in there. At start up, you have a reduced voltage because of the starter so what happens is the ballast resistor is bypassed during start. If you get rid of the ballast resistor and put an internally resisted coil, you won't be able to put this higher voltage to the coil so you will have a harder time starting.

 

[vinnie1234]

Bruce has it right. I must admit I'm a little rusty with points ignition systems. I'm an auto mechanic but we don't see much of these ignition systems anymore. Most of the old car guys work on the stuff themselves. Because you have somewhat conflicting posts here I feel I should let you know that my description of the resistor operation is incorrect.

The thing to take away from this is that the resistor is bypassed during start up. The bypass increases the available voltage, so it likely isn't your problem.