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1975 40hp evinrude 40554c ignition trouble

E

edthead

New member
bought a 16 ft jon boat with trailer and 40hp motor. trying to repair the motor, had a broken ignition swithch and the blue and blue/white wire were hanging out the front of the motor. Ordered a replacement switch from sierra their pn# mp39760. Hooked up the red wire to terminal B, white wire to terminal S, purple wire to terminal C, and the blue and blue white wire to the M terminals 2ea. This leaves the A or I terminal open, which is the only other terminal to be hot during run. I have the following going on, Starter cranks when key is turned to start, Choke clicks down when key pushed in, Still no spark during cranking. I checked the coils and one was cracked, the other one seems fine, but ordered 2 replacemnt ones from sierra. I pulled the flywheel and one set of points looked burnt, but passed the ohms test, so I sanded both sets and re gapped them. I checked for voltage at the points blue and blue white wire and there is none. There is no voltage to the coils either. The Top Terminal on the relay block near the rectifier has 12 volts but none of the yellow wires 3ea have voltage. The reason I need voltage at the yellow wires is that they run to the Magnet things next to the points. Question that I can't figure out is if the blue and blue and white wire is not hot at the run position of the ignition switch, where is the voltage for the igniton points and coil coming from?
 
????-----------The voltage comes from the magneto for ignition.--------The battery has nothing to do with making spark for the plugs !!!!!
 
edthead, you got it all wrong. There is a coil under the flywheel called a driver coil. It generates the electricity for the ignition spark. When the points open, they send a jolt of electricity to the external spark coil, which amplifies it up to spark voltage.

The yellow wires to the rectifier come from the alternator coils, also under the flywheel. They generate electricity for charging the battery, and of course there is no voltage there unless it is running and generating.

Those are two totally separate systems, not connected to each other. And battery voltage does not power the ignition coils.

If I read your post correctly, you have it wired correctly. Do not expect to find any measurable voltage at the blue wires. As I said, that comes in the form of fast pulses. The blue wires at the key switch are to stop the motor when the key is turned off.
 
Hey, thanks for all the help, I understand how it works a little better, After the post yesterday I went out and looked around at the motor on the starter side, I noticed on the Vacuum cut off switch that the blue and white wire seem to connect to the center of the switch and when I tested this with an ohm meter it was an open circuit, I assume that when this switch gets to much Vacuum it closes the circuit and allows the switch to ground out the wire? I also noticed that there is a second wire that runs from the Vacuum switch mounting bolt upward to a small square switch that seems to touch some kind of a flat plate. This wire has no insulation left on it and the wires are starting to corrode. What is this wire, is it just a plain wire I need to replace or is it a resistor wire?
 
Kim, I see the double lines on the outer edge of the fly wheel, but not sure where the single line is located. I have a automotive timing light but it won't work with out spark, do you think the charge coil is bad, if so how do I check it?
 
Oh one more thing that I just remembered that might be related but not sure. On the Joh Boat just in front of the rear seat is a little console that has the light switch, the Horn switch, and one more switch that I don't know where it goes. Could this be a kill switch, not sure how it could be as it is hooked on a relay board with all the other items just listed and the relay board is a simple 2 wire hook up directly to the battery? Any thoughts?
 
Kim, the safety switch that won't let you crank the motor unless it is in neutral is just to the left and lower then the smaller white switch with the bad wire.
 
Success, 1 Ignition switch, 2 coils, 1 tune up kit, and it runs, off to the river to try it out, thanks everyone for your help
 
Ok, back from the river with a few issues, Motor Started but wouldn't idle, WOT it ran well for about 2-3 minutes then one cylinder dropped out and the other would continue to run fine until throttle moved from WOT, then it would die, while running on one cylinder the other cylinder would fire once or twice causing the boat to jolt, hard to start engine after it dies, throw out the anchors, fish for a while and then try to start the motor, once running on 2 cylinders again, same story 2-3 minutes of good hard running motor and then down to one cylinder and finally die out when Throttle moved from WOT. I have a see through fuel filter and it shows full of fuel and no dirt what so ever. Would I be wrong to try and disconnect both the safety switch and the vacuum switch and see if it runs longer and better? I've ordered a carb rebuild kit and a fuel pump rebuild kit just encase. I'm wondering if my skills setting points is a little rusty and the reason the cylinder is cutting out is the coil is over heating from working to hard?
 
Cora Wydeck-Kralevic said:
Whatever happened, was it the points that was making the cylinder not fire correctly??
Click to expand...

yes and no, after I removed the flywheel, (points are located underneath) I found 1 set of points to be burnt, So I replace both sets. I took it to the river and the motor would start at idle but die when shifted into gear. So I reved the engine up and dropped it into gear and was able to get about 3 minutes at full throttle, after 3 minutes one cylinder would drop out, almost acting like a coil had been shut off due to over heating but I would stop and fish for about 20 minutes and I would be able to restart the motor and rev it up, shift it into gear, and it again would run for only 3 minutes and drop a cylinder. repeated the above twice more and I couldn't get it to restart so we paddled back to the launch ramp and went home. I thought maybe the carb was the problem, So I removed it and rebuilt it. ( the carb was spotless, not a spec of dirt anywhere inside it). So then I rebuilt the fuel pump, I have got the engine to run every now and then but the midrange still doesn't work. So I'm going to have to take it to an expert who can tell me if the electrical system is grounding it self out when the throttle handle is moving. Oh, I also rebuilt the water pump, which surprisingly wasn't that hard. I'll try to check it out some more after the 4th. I have smaller engines in all manner of repair so I've got other options if I can just get one to fire up. Thanks for asking, and a warning, if you are an automotive mechanic, you'll have to learn how the electrical system works on boat motors, do not try to repair it like you would a car, or you'll burn up alot of stuff. There is a site on the internet that has a free motor repair guide for the 40hp evinrude and you still can get repair/rebuild kits for most items on the 1975 but floats and whole carbs and other things aren't available, unless you find someone who is scraping their motor.
 
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