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Discussion Starter #1
I have a 1965 Honda S65 that has an electrical problem. I have installed a new battery and the bike starts on the first kick. When I first started it, it did not have a headlight or tail light bulb installed. It ran very well. I then installed a bulb in the headlight and the bike ran very poorly. It would cut out when the throttle was opened. However the headlight was on. I discovered that there are two on positions on the ignition switch. I believe the first starts the bike without lights on and the second turns the lights on. I have always put the switch in the second position. I put the switch on the first position and the bike ran great again. However the headlight was not on as expected. I checked the bulb and it is not burned out.. However I also discovered that the 7 amp fuse that came attached to the positive lead of the battery was blown.
My theory is that when I put a bulb in the headlight and started the bike with the ignition switch in the second position (lights on) something blew the fuse on the battery. This left the bike running on the magneto only. For someone that understands the magneto/battery system on these bikes, does this make sense?
Any ideas on how to determine what caused the fuse to blow.
 

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Vintage Rider
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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.
 

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Discussion Starter #3
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.
Rizingson, thanks for the reply. I will do some more trouble shooting using the information you provided. I do have a couple of questions though. Can you tell me what the difference is between the two on positions on the ignition switch. Is the first position for no lights and the second position for lights on? Second, I installed a new Yuasa battery and the fuse is on the positive lead not the ground side of the battery. Would that make a difference?
 

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Vintage Rider
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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.
 

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Discussion Starter #5
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.
Thanks again for the response. I am going to do some testing with the switch in position 1 and 2, the headlight bulb in the socket and out of the socket and the tail light bulb in the socket and out of the socket. This should tell me what combination of conditions causes the engine to run poorly. From there I will know what circuit to trouble shoot. I will probably get back to you with more questions.
 

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Discussion Starter #6
Thanks again for the response. I am going to do some testing with the switch in position 1 and 2, the headlight bulb in the socket and out of the socket and the tail light bulb in the socket and out of the socket. This should tell me what combination of conditions causes the engine to run poorly. From there I will know what circuit to trouble shoot. I will probably get back to you with more questions.
I put new bulbs in the headlight and tail light and I replaced the burned out 7A fuse with a 10A fuse. I was able to do some more testing and here is what I found. When the ignition switch is in position #1 (lights off) the bike idles and runs fine. When the switch is moved to position #2 (lights on) the headlight and tail light come on but the engine immediately starts to cut-out both at idle and when you try to speed it up. Neither of the bulbs is blown out. When switched back to position #1, the engine immediately runs fine again. Using the information provided earlier, is it possible that when the lights are switched on the charging/lighting coil is not putting out enough amperage or voltage to keep the engine running smoothly? If this is the case, how would I test this? If not, does anyone have any other ideas?
 

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Vintage Rider
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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.
 

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Discussion Starter #8
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.
Thanks again for the input. I will disconnect the ignition switch ground wire and see what happens.
 

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Discussion Starter #9
Thanks again for the input. I will disconnect the ignition switch ground wire and see what happens.
I disconnected the ground wire from the ignition switch and the engine now runs much better in switch position #2. Almost all of the cutting out is gone. I can still tell that the engine runs smoother in position #1 but it now runs 90% better than it did in position #2.
 

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Vintage Rider
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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.
 

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I'm not sure expensive that switch is or how difficult to change but I'll admit, I would have looked hard at just replacing that switch almost from the get go given that all the wiring seemed correct and getting drastic different results than expected at the switch. I would have just replaced it. I commend you guys for going through all this checking to prove it probably is problem. So I would have taken the lazy way out I'm sure. But then wondered after if it wasn't just a coincidence that things started working correctly. So...BRAVO !
 

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Discussion Starter #12
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.
I looked for a replacement switch on Ebay and they are $100+. My plan is to wire in a kill switch, bypassing the ignition switch. When I restored the bike I replaced the points and condenser so I expect they are not the problem. I am still baffled as to why the problem only occurs when the switch is in position #2 even with the ground wire from the switch disconnected.
 

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Discussion Starter #13
I thought I should provide an update to the electrical problem I was having with this bike. I took Rizingson's advice and started to look for ignition components as the cause of the misfiring. I had already replaced the points and condensor and reset the point gap several times so I moved on to the primary coil and the ignition coil. When I tried to measure the resistance of either of these with my two cheap multimeters, I would get inconsistent readings. Not wanting to buy a more expensive multimeter, I dug around in my parts bin and found another ignition coil and decided to give it a try and installed it. With the ground wire from the switch still disconnected, the bike started fine and ran fine with the switch in both positions #1 and #2. I then reconnected the ground wire from the switch and it still runs fine in both switch positions. I can only conclude that the problem was a bad ignition coil all along.


Thanks Rizingson for all your help.
 
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