I’m putting this puzzle out to The Wisdom of the List:
I’ve been having an on-going problem with my fuel gauge. When the ignition is switched ON the fuel gauge sweeps to full and then normally
it drops to whatever the fuel level is. However over the past few months, if the fuel gauge reads one bar above half, or less, and I park the scoot for the night (on the center stand, in an attached garage) and return the following morning the gauge sweeps to full then drops to reserve flashing. This will continue to happen until I refill the tank, in which case the gauge will sweep to full and then drop to whatever level the fuel is above that “one bar above half” level.
Now, when I take the scoot out for a ride and go approximately 2-3 miles the gauge will gradually begin to rise; first one bar, then another, etc. until after about 6-8 miles the gauge is up where it belongs. If I continue on my way the gauge will drop normally and a about 130 miles I refill the tank. During that initial 1-2-3 bar rise if I shut the bike off for a few minutes the gauge will revert to reserve flashing again, but soon correct after I start riding.
This problem began in late spring and I started adding Techron when filling the tank and also added Seafoam. After several tank treatments I switch to a premium fuel (Shell) thinking that it’s claimed detergent properties would help.
The scoot sat, unused, in the garage for a month with a full tank of Shell along with Seafoam while I was recovering from a medical issue.
Last weekend I decided to reacquaint myself with my riding skills and went for a day long 120 mile ride. The gauge performed completely normally. It never missed a beat, even after stopping several hours for an extended brunch. With 120 miles on the odo I refilled with Shell before stopping for the night. The next morning the gauge swept to full and remained there.
Two day later I went for another ride and returned with about 80 miles on the odo. The next morning the gauge swept to full then dropped to reserve flash. So much for my detergent properties of Shell fuel theory.
After much consultation with the wiring diagram and checking several internet posts I suspected that my problem was due to sulfur and crud deposits on the fuel gauge sending unit, but given all the Seafoam, Techron and premium fuel treatments, that remains to be seen.
After that 80 mile ride, and the gauge going to “one bar above” before parking for the night, I plugged in the battery charger thinking that something is partially draining the battery and that a full charge will fix the problem. I let that charger work its magic for over 24 hours, and when I turned the ignition on the gauge swept to full then dropped to reserve.
So without jostling or moving the scoot I fired it up and let it idle for a full 20 minutes, all the while watching the fuel gauge and the temperature gauge. After 20 minutes run time the temperature gauge was well into the operating range and the fuel gauge was merrily flashing away like a grannie on the freeway with her turn signal still on.
So the gauge will read full with a full tank; it will read normally throughout the full tank range if a full tank is used in one ride; it will drop to reserve overnight; it will gradually resume working over, maybe, 8 miles; the problem will reoccur if the ignition is turned OFF too soon; the battery is at full charge; and it doesn’t appear to be a function of run time; the fuel sending unit float is nothing that can get filled with fuel and drop to the bottom, or otherwise bind.
What is it that happens overnight which causes this issue?
It seems to me that if the problem were a failing component on the Combination Meter circuit board / fuel gauge that the 24 hour charge and/or the 20 minute idle (far longer that it would take to ride those 8 miles) would have been adequate time for that component to restore itself.
Any ideas, anyone?