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73 Evinrude 25 hp Spark Problem

K

Ky Howard

Contributing Member
I have a 1973 25352A and I can't get good spark. Things I've tried: New Sierra driver coil, New Sierra 2ndary coils, Resistance checked and in spec) new plug wires-continuity, cleaned and regapped the points, tried at .017, .018 .019 .020 .021 and .022 gap. Positioned drive coil armature squarely .003 from magnets with and without gage. Replaced wires from points/condensers to secondary coils, tested and changed condensers after testing (each at least .290 Microfarads, flywheel magnets are strong. Spun the flywheel with a drill at approx 750RPM and the best I can get is a tiny pin point spark both coils. Engine has 140 psi compression but haven't started it yet since the carb needs to be cleaned and the starter tuned up. I'm afraid that weak spark won't fire it. Any suggestions to get a fat spark?
 
Thanks for trying to help. Points are simply a switch. I removed them, cleaned them and removed dirt, irregularities, and resistance verifying they are square with each other. Then I checked them for shorting and remounted them. Same with the condensers. I checked them for leakage and found them within spec., and at an acceptable level of capacitance. I don't believe in changing stuff "just because".
I thought it may jog someones memory about this driver coil type magneto system and they would remember it.
 
I understand they are a switch but 53 years and how much time to remover the flywheel?
Have you considered the phenolic "bushing" at the pivot point of the points could be contaminated or cracked allowing voltage to short to ground there? ***When I say short, I am suggesting the voltage spike as the points open, something that won't show up with a VOM.***
 
Worrying about whether your spark plugs are at any of the ranges you mentioned is a complete waste of time. A good strong blue spark should jump at least a 3/8 inch minimum air gap.
Once you get that, then, maybe you would look at putting new plugs in, but expecting to change the gap by a few thou is a waste of time
 
Droid said:
Droid said:
I understand they are a switch but 53 years and how much time to remover the flywheel?
Have you considered the phenolic "bushing" at the pivot point of the points could be contaminated or cracked allowing voltage to short to ground there? ***When I say short, I am suggesting the voltage spike as the points open, something that won't show up with a VOM.***
Click to expand...
Now that’s a good point Droid. A high voltage spike will find leaks where the limited voltage during a resistance test won’t. I will check that out.
Click to expand...
Th
 
Droid said:
I understand they are a switch but 53 years and how much time to remover the flywheel?
Have you considered the phenolic "bushing" at the pivot point of the points could be contaminated or cracked allowing voltage to short to ground there? ***When I say short, I am suggesting the voltage spike as the points open, something that won't show up with a VOM.***
Click to expand...
That's a good point Droid. I experienced a phenolic? (type) insulator on the Mercury points system that did that. It was cracked in a location out of sight and took a while to figure out. I hadn't thought of the bushing doing the same thing. A high voltage spike can certainly find a leak where the low voltage during a resistance check would not. I will look into that.
 
Edchris177 said:
Worrying about whether your spark plugs are at any of the ranges you mentioned is a complete waste of time. A good strong blue spark should jump at least a 3/8 inch minimum air gap.
Once you get that, then, maybe you would look at putting new plugs in, but expecting to change the gap by a few thou is a waste of time
Click to expand...
Thanks EdChris177. I made no changes to the spark plugs. I was changing the gap on the points. That increases or decreases dwell time and alters not only spark quality but also advances and retards timing slightly.
 
and one more thing Droid. 53 years ago I was on the South China Sea in the fireroom on the Carrier, USS America. It doesn't seem like that long ago.... and as for the flywheel. Since the plugs were out I was able to set the flywheel in place and just snug it down with the nut, then use a 1/2 inch drill to spin the motor. It turns at 750 RPM which is more than fast enough to energize the system. Then by removing the nut, and tapping lightly with a hammer the flywheel loosens quickly.
 
fitz73222 said:
Disconnect the two kill switch leads and check spark.
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Thank you but yeah, I’ve had them disconnected from the start. I’ve got to start over from the beginning I guess. I’m going to try another flywheel on the outside chance the magnets are not strong enough.
 
Ky Howard said:
Thanks EdChris177. I made no changes to the spark plugs. I was changing the gap on the points. That increases or decreases dwell time and alters not only spark quality but also advances and retards timing slightly.
Click to expand...
My mistake. You’re right. I saw the word sparkplug, but missed that you were referring to points.
 
According to my Merc-O-Tronic reference material your condenser capacitance should be reading .18-.22 microfarads.
I happen to have the exact model year engine as yours in stock. I went back to 1962 when P/N 581419 became the same condenser used up until the mid seventies for the 18, 20, and 25hp models. So a reading of .29 as you are getting may be in question. Also, loss of magnetism in the flywheel magnets pretty much went away after WWII when the materials changed.
 
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