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Honda S65 electrical problem

8K views 23 replies 7 participants last post by  DannoXYZ 
The S65 has a magneto ignition system. Whether the battery is installed or not has no effect on the ignition circuit, or the way the engine runs. The battery is charged from a lighting coil. That is shunted for running without lights. It's a balanced charging system. When the lights are on all the windings are used for extra charging capacity to keep up with the load on the battery. The fuse is on the ground side of the battery. If it is blown you will still have headlight, tail light and instrument panel light, as they run on AC from the lighting coil. The horn, neutral light and stop light are DC and are powered directly from the battery. If the battery is in poor condition or fuse is blown, it will cause the charging/lighting coil to put out too much amperage and high enough voltage (up to 30v when engine is revved) that usually blows the bulbs that are on the AC circuit, since it's output is balanced for everything to be working. I would still check for dirty connections, bad ground or a direct short somewhere in the system using a digital meter. Sorry I'm not better at explaining electrical than I am working on it. I know this sounds crazy but the bulb in the tail light has two filaments, one turns on with DC the other with AC.
I've owned a few S65's and still have a couple in my collection.
 
You are correct about the switch positions. Also it doesn't really matter as far as I can tell on the fuse position. I believe mine are also on the positive side. It's probably a mistake on the drawing.
 
Sorry for the late response. As was mentioned in my earlier post, there is no cross connection between the ignition circuit and lighting/charging circuits, if wiring is routed correctly and all systems are functional. Since you appear to have the ignition cut-out when the key is in the #2 position (lighting) it would appear that the ignition switch itself is faulty. (causing the black wire to intermittently go to ground internally in the #2 position) For the ignition to cut out, as described, it has to be grounded to the frame through the switch. I would recommend trying to isolate the ignition ground (used to shut the motor off only) at the bullet connector near the switch (black wire) This will allow the lighting to still work but not allow the switch to shut off the motor. Also make sure there is a good ground between the switch body and frame. This ground is required for lights to work as well as engine shut off. Caution: with that black bullet connector disconnected, the motor will start in all three positions and cannot be shut off with the key. To shut off motor you may need to either choke it, stall it in gear, or pull the plug wire. If this test works and allows the engine to run fine with the key in #2 position, you will need a new switch, or if you are very lucky some electrical contact cleaner sprayed into the switch while working it back and forth may eliminate the cross connection.
 
Well, that's a good sign, in the fact that the main switch has problems within. This is also the likely cause of the fuse blowing for no rational reason. I'm also thinking some of your remaining issues with misfiring is simply ignition component problems or less likely fuel issues, such as starvation under load. Most likely of which would be the points being dirty or mis-adjusted. If this missing is more noticeable when you are putting the engine under load ie accelerating or at high rpms this would also indicate dirty points. Condenser and coils rarely go bad. I would replace the switch or if you have the ability you could add a kill button to ground the ignition circuit to shut off the engine without going through the switch. Also on a side note, is there a possibilty that the ground wire from the ignition switch is frayed somewhere else that could also be causing some problems, although that would be a problem in both running positions.
 
Thanks I recently had all the bulbs blow on the bike and it would idle but not rev. Going to change the rectifier,its 57 years old. Hopefully that will sort it.
The fact that the bulbs blew indicates the charging system is working. High voltage blowing the bulbs. The problem is more likely a battery that cannot except the rate of charge being fed it through the rectifier. Sulfation limits the amp hours the battery can except or put out, even though voltage may remain above 6 volts. Since the S90 has no regulator the battery acts as the regulator. Not being able to receive the voltage due to battery size, sulfation, age etc disrupts the voltage balance in the system. The old rectifiers do go bad and leak ac current also, since they aren't expensive to replace that may not be a bad idea along with a new properly sized 5.5hr battery.
 
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