I would think that a gurgling sound in a tank would indicate air or maybe liquid being pumped in, or disturbing the existing fuel somehow.
That system has a BUNCH of hoses & stuff going on. I'd want to consult the FSM on all that.
After 45-50 years, I wonder if it's all still working correctly.
If the carb bowl is open to atmosphere, it can lose fuel through evaporation.
If the carb bowl is sealed, as in part of that system, I'd wonder if heat expansion is returning fuel to the separator and/or tank.