Well, it happened. The stator in the alternator failed, as they tend to do in Ninja 650Rs. Mine got me almost to 66,000 miles, so I am pretty happy. It also didn't just let me down in the middle of nowhere, fortunately.
The stator is wired in a three phase pattern, and one of the phases was not producing an output voltage.
I think the failure is right where the burned place is in the photograph below.
That failure made the stator produce less power to recharge the battery and run lights, ignition, fuel injection, and accessories. I noticed that occasionally the horn was not very loud and the trip odometers and clock would sometimes reset to zero when starting the engine. I tested the stator according to the Kawasaki manual and found the problem.
The stator OEM part number is 21003-0042 for my 2006 and others. I bought a new stator from grimcycles on ebay, and it got here in about a week. It looks good and fit fine. More importantly, it now produces the full power that it should. That cost me $144.95 for the part, shipped. My labor, as usual, is free.
I changed the oil and filter as long as I was in there. You lose most of the oil when opening the stator cover if you do it with the side stand instead of a rear stand. If you use the latter, you only lose about a quart. It needed changing anyway, so that was fine. I use Mobil 1 and a Kawasaki-brand filter.
The procedure to change the stator is well documented here. I reused the stator cover gasket. It is not metal, but it is sufficiently sturdy if you are careful handling it. Use silicone sealant only around the wire passthrough, not on the entire gasket.
I buttoned up the engine, filled it will oil, started it up and found that the charging voltage at 4000 RPM was correct at 14.6 volts.
I went for a ride, and the symptoms of the weak horn and disappearing odometer reading persisted!
Well, I tested the battery after it had been on trickle charge overnight and found its voltage to be lower than it should be.
That is an indication of a bad battery. I last replaced the battery in late 2012, almost 30,000 miles ago. That time, I replaced it with the same as OEM, a Yuasa YTX12-BS. I did the same this time, and found it only a few dollars higher than six years ago at $59.88, shipped from Amazon seller Avid Cycles. It got here in a few days, I filled it, charged it, and everything works fine now.
Oh, wait a minute. What about the tire I mentioned? Well my front tire was about worn out so I sent away to Sportbike Track Gear for a fresh Michelin Pilot Road 4. They had the lowest price of $146, shipped when I used an $8 rebate from previous purchases there. I took it to the local Foothills Powersports dealer to be mounted and balanced for $37. The worn out tire had 10,500 miles on it and the resulting cost per mile was $0.018 over its life. Even at as long a life as I get because I ride sedately, tires are a significant expense of owning a motorcycle.
So I have two good tires, and an electrical system that works properly now. The whole escapade cost about $390. This motorcycling isn't cheap!
I might say, though, that this bike has been very reliable over its life. I never abuse it, so that probably contributes to its longevity.
The other major issues -- besides routine service -- have been the fuel pump failure, the loose kickstand, and the water pump seal failure at 41,000 miles. I have done all of the maintenance and repair myself, so the costs were much lower than if I had to take it into a mechanic each time.
Not too bad for an elderly ride like mine.
Hope to see you on the road!