The bike starts normally. It will at times start running lean, like fuel starvation, but then will come back to life. Eventually, it will start running lean, and will quit from fuel starvation. Hitting the starter, it jumps to life again and rides off like there was no problem. This happens every five minutes or so.
Checking the fuel pump, when the bike is started, it runs for a few seconds - click click click, maybe 5-6 clicks per second, and pumps fuel normally. It will then stop, until (I assume) the carb float needle valves drain off some pressure, at which point the fuel pump will start back up again for a few more seconds.
Eventually, the fuel pump will NOT start back up again, it will sit for a minute or more without running, and the bike will die from fuel starvation. Hitting the starter, the fuel pump jumps back to life, and the bike starts normally.
The battery/bus voltage is a solid 13.8V. I checked the fuel pump relay, which appears to be a potted, solid state relay, and it is a fluctuating 6-8 volts being supplied to the fuel pump. The primary of this relay is driven off one of the spark coil primaries, so I suspect there are pulses of 12 volts coming off the relay going to the pump, but my digital meter isn't capable of resolving that into +12v fast enough, so instead it's fluctuating around 6-8 volts.
Running +12V directly into the fuel pump causes a solid buzz and fast pumping, not at all like the "click click click" it is doing while the bike is running.
I checked the fuel cap to make sure it is not clogged and causing a vacuum - running the bike with no fuel cap in place, the problem still occurs.
The fuel cut relay, without question, is definitely solid-state. And it's not just a relay - it's modifying the signal. Here is the pulse coming from the ignition control module, which is sent to one coil, the tachometer, and the fuel cut relay:
The output of the fuel cut relay rises quickly to 12 volts when triggered by the ignition pulse, but then tapers off down to zero just before the next pulse. This is shown at idle - if the engine speed is increased, the taper does not reach zero before the next pulse occurs. This leads me to believe that there is a capacitor inside the fuel cut relay, that is discharging to extend the pulse. If the engine speed is increased high enough, the pulses are almost invisible, and essentially a continuous +12V is applied to the fuel pump.
So this is all well and good, but none of it tells me why the bike is randomly dying of fuel starvation. As luck would have it, while I had the scope hooked up, the bike was operating perfectly, with the pump clicking away every few seconds, keeping the bike alive.
From research I did tonight, I found that the pump is quite reliable, and the fuel cut relay is usually the failure item. I've ordered a replacement relay, and we'll see if this solves the problem. I've also ordered a petcock rebuild kit, as it has the same type of vacuum petcock in it as our Goldwings.
So my question for GL1200 owners is this: on the GL1200, which uses the identical fuel cut relay/pump layout, what do you measure on the output side of the fuel cut relay? If you look at the fuel pump, there is a white wire that leads to the fuel pump connector, where it connects to a Black/Blue wire that actually runs to the fuel pump. When the bike is running, what voltage do you see there?
