Fuel tank vent discharge 23 CC Inboard and bluefish

[GetReel]

OK, I hope that someone has run into this dilemma or perhaps I'm an idiot?

I'm trolling for stripers (sorry to report just bluefish) the other day and my buddy smells fuel on my 23 CC inboard. We check the port tank vent and it is discharging fuel overboard in a steady stream. Please note that the tank was only 1/4 full. I switch tanks to starboard and also return line to starboard and it stops. I then open (slowly) the port tank cap and it releases solid air pressure (not fuel). I had just checked the port vent line the other day and seemed clear because when fueling up from the previous day I noticed the tank didn't seem to vent well and kept burping. Because I pushed fuel thru now it has to be clear? The starboard tank seemed fine, but just to see, I flip the return line back to port and leave the fuel supply line on starboard, within seconds the starboard tank vent dumps fuel. I did not switch back to port tank again as I was now trying to avoid EPA/DEP sanctions...and more bluefish.

If any one thinks they have a clue on this please let me know...I'm running a single IB 454 MPI MarinePower-engine is only 2 years old and both 50 gal. tanks are 2 years old also as well as all hoses and gauges etc. I have two 3 way switches. The selection is Port, Starboard or Off. I always marry the switch so that I pull/return from/to the same tank, either starboard or port. My fuel return lines run back to the three way switch and then to the tank.

The only thing I can figure is that I had crossed the settings, or, the return switchs are labled reverse? but, the tanks were'nt close to full anyway, so why the discharge???This has not happened before so I'm somewhat mystified-no sign of fuel in bilge either...damn bluefish.