The tank on a California II has a spout that goes down into the tank about 2 inches.
If you overfill the tank to a point where this spout is dipped in fuel and leave the bike in the sun the air inside warms up forcing the fuel up the spout and out the filler all over the engine.
Easy solution
Drill a tiny hole through the side of the spout up near the top, this lets the air pressure dissipate and also lets you cram about another half a gallon into the tank.
Center punch first or the drill will wander off, I used a hand drill for safety.
