Iím an Electrical Engineer specializing in power supplies, and I have owned a VN750 since 1992 (1993 model). I have almost 60,000 miles on it. Iím very happy with the bike except for the electrical system. It is the worst designed motorcycle that I have ever seen in that area. Almost nothing has been done right! I had to rewire, and redesign, the motorcycle to get the kind of performance that I think I should have had out of the box.
I see two major complaints, in general, about the electrical systems. Not only are these complaints on this forum, but I have known others, personally, with the same bike and with the same problems. I believe that I can help many of you.
First, I am on my third stator - and it has failed. Every failure has been a short between the windings and the laminations, which are connected to the engine case and the frame. This is a most annoying failure for at least two reasons. One, it results in poor battery charging which can leave you at the roadside in the worst places. And, two, the poor design of the Engine mounting means that you have to essentially remove the engine from the frame to get the cover off for access. (I realize that a full removal is not necessary.)
This is so much time and work again, that I am considering cutting the frame for future access. I certainly wouldnít recommend this if you are concerned about resale value, and, of course, the frame must be repaired properly! For this last failure, I built a power converter that will allow for a single short in the stator. I canít recommend this either since I spent way too much time on that design, but, at least, I was inside the house most of the time. Also, it is likely that a second short will develop, in time, and kill this idea.
One thing I now know for sure Ė the Kawasaki stator is a waste of money. For about $300, you are lucky if you can get a couple of years out of it! Electrexworld in the UK offers a replacement that is about 1/3 the price, and it seems like it canít be any worse! (I havenít purchased one yet from them.) Because of the poor reliability, however, the cost of the stator is not the major issue. Iíve also added a LED circuit to tell me when the battery is being charged. Itís a little tricky because the voltage drops in the wiring lower the voltage significantly near the handlebars. You have to compensate for that, and if the headlight should quit, the compensation would be all wrong.
Incidentally, should you get stuck by the roadside with what seems like a bad battery, it might be possible to get going again if you disconnect the headlight. Letís assume you can get started by pushing, or rolling down a small hill. The headlight may remove enough load for the remaining stator windings to run everything else. It worked for me.
The biggest complaint seems to be the poor starting. Yes, a good battery can help, but the real problem is the wiring drops and poor tolerance for low voltage in the ignition circuit. My first approach was to build a boost circuit for the voltage to the ignition circuitry. It would keep up the voltage, even when the battery was cranking near 8 volts. The starting was nothing short of miraculous! A short stab at the start button would immediately bring the engine to life. Battery quality was unimportant as long as it could turn the engine over. What wear and tear I had previously given to the poor, abused, starter motor was not going to increase any more.
This seemed a perfect solution until I later discovered that there was a more fundamental problem, and much easier to fix. I lost a connection to my boost circuit, and while I was contemplating the situation, I began to probe around some more. The wiring on the motorcycle is designed with rather minimum wire size. I assume this is to save money, however, as I have observed on this site, there is a tendency for the wiring to overheat and burn in a few areas. I too, have had burned connectors in the stator wires.
The battery voltage is wired through the ignition switch and back to the ignition circuits. With all the loads, including the headlight, there is considerable drop by the time it gets to the ignition circuitry. The solution was actually quite simple. I purchased an automobile relay, available through Radio Shack, and others, and inserted it between the battery and the ignition wiring. (You need at least 10 amp contacts on the relay.) The relay wiring must include the primary wiring of the high voltage coils, one of which, is under the gas tank. You must remove the wire connected from this front coil to the ignition switch. Then wire the front coil to the relay contacts along with the other high voltage coil near the battery. Additionally, also wire the ignition circuit to this same contact. Use some heavy gauge wire to do this - #14 AWG would be good.
Now connect the wire that was tied to the ignition switch to the relay coil, and tie the other side of the relay coil to frame, or chassis ground. You donít need heavy wire for this connection, but make sure it is a good quality stranded hook-up wire, and it is best to use Teflon insulation, if you can get it. This will avoid burn-through from any hot sources, and also helps with chafing. There is plenty of room for the relay, close to the battery.
I canít be sure that this later solution by itself will cure all starting problems. I have a maintenance free battery now, and the boost circuit doesnít seem to provide any advantage in starting when added to this change. I suggest getting a wiring diagram with color codes before you start. Know what you are going to do before you start, because wiring errors could cause significant damage. Good practice would be to disconnect the battery, and check everything with an ohmmeter, or continuity tester. I would like to know how well this works if anyone else tries this modification.