Even though full, tank level gauge will fluctuate between empty and full and all points in between. Where to start?

 

A lot of folks will tell you the sending unit; I'm on the 3rd fuel gauge on my '02 RG. You can test the sending unit with an ohm meter, but you gotta pull it to do that. Which if you're due for a fuel filter replacement would be OK, otherwise it's an additional expense and PITA. It's easy to replace the gauge.

 

Probably the gauge, common problem.

Just watch gauge when you first start the bike.

If it pops swiftly to the tank level, the gauge is probably gone.
It should move slow and steadily.

The needle has internal damping, and once that fails the needle starts jumping around.
.

 

Have you just returned to riding after the bike has been sitting for months? My fuel gage was giving me fits for a couple of months after being warehoused over a year. Its accurate again (as well as it ever was) after riding a few thousand miles.

 

Based on experience, im betting the gauge itself is crapping out...or is crapped out.