Classic/Antique Car Repair: Nova gas tank mystery, vent lines, vent line

Question
Hello,
I recently bought an unmolested 71 Chevy Nova 350 2bbl four door with 80,000 original miles. For some reason, when refueling the tank the fuel spurts out the filler neck.  The only way to avoid it is to trickle the fuel in at an agonizingly slow rate and it still sometimes surges back.  I have checked the line leading to the evaporative canister and it is clear. I have tried refueling with the hose disconnected from the evaporative canister and it still splashes out.  Any thoughts?  Thanks much.  'Great service you provide!

Answer
There are three vent lines that run from the fuel tank to a liquid vapor separator. This unit may be mounted between the back seat back cushion and the trunk. The vent line to the canister runs from the separator. The problem could very well be in the lines running to the separator or in the separator itself.
Brad