Fuel Selector Switch issue

[Anne Bonny]

In our '95 355 ACMY, we have three tanks, starboard, port and aux. We understand how they work, each engine can pull/return from their respective tank or the aux tank, no issue there. Starboard side is working as it should however, we are having an issue with our port side.

When port fuel selector switch is set to supply and return to/from aux, we have noticed the port side does not actual supply from aux however does return fuel to aux.Essentially transferring port tank fuel to aux tank.

So question is... What could be preventing the port engine not to pull fuel from the aux tank? We have replaced the port supply switch(switch only) this season but didn't resolve the issue.

Fuel lines have been traced and appears to all be connected as should. We have found one line from the aux tank with a spark plug plugging it not entirely sure what this line is used for and why it was plugged in this fashion. All fuel filters replaced.

Any suggestions on what the issue could be?

Thank you,
Wifey

[g36]

my 405 has 2 tanks under the platform instead of your one aux, 2 fuel lines each from each tank to the selector valves. first there should not be any line from a fuel tank plugged with a spark plug what location is this plug on the line? near the tank or the fuel valve?. as you know this is pretty straight forward. pick up and return fuel to the same tank through the selector valves. assuming this since i dont have a 355 have you traced all 4 lines from this tank? i would again verify that the lines to the valves are correct position because it seems that ones on the port side are crossed from port main to aux ( supply side) if the spark plug is plugging a pick up from the aux tank then that needs to be fixed. does it come from a fitting on top of the tank with a check valve on it (anti siphon valve)? this would indicate its a supply line connected to a fuel pickup in the tank which could be your problem.