Spectra belly tank

[Skee]

I don't know if anyone here can or will help, but I have a question....Last year I bought a 1974 Spectra 18 (which I really dig)...Anyway, it has a belly tank, filling this thing with gas has been a pain in my ass, it burps back up through the fill hole about every 0.40 cents or so, unless ya go SUPER slow. Yesterday I got into it, the vent they had on it was at the very top of the fill hose (they added it into the the fill cap nozzle) to the side of the boat. I realized there was no vent at the tank, I took up the floor yesterday (found out it's a full stringer boat) anyway, the tank was replaced in 1982 from a place in Costa Mesa which is no longer around, but when they made the tank, they put no vent "into" the tank as is needed and the other one they put on there was too high and not working. Can anyone suggest a fix for this without having to remove the whole tank from the boat?? Thanks in advance. Skee

 

[SPECTRALEN]

Some pics might help in figuring out a solution.
The vent is to let air into the tank as your fuel pump takes the fuel out, preventing a suction type of lock up and acting as if you are out of gas. My saddle tanks have no vents and I had to drill small holes in my caps to create a vent. I'm wondering if your long fill hose is a flexible acordian type with no kinks or a stiffer kind that might be giving you a flat spot?