RE: Fuel intake
I've had some fun with this in the past including getting me and half the boat covered in a blowback -ooops.
The tank vent may be too small and not allow air to escape as fast as needed. Take a look at fittings and any reducers. The actual tank fitting may be large enough but if a P.O. used reducers to make a small hose fit, that may cause trouble
If a dip occurs in the vent line hose it can fill with fuel and make air escape difficult or impossible.
The hose may be kinking as you replace it.
The wong type of hose material can get mushy and maybe swell partly closed over time.
The screen, there usually is one, inside the actual vent fitting on the hull may have plugged over the years or maybe bugs have decided to make a nest. The screen is there for safety reasons but it may need to be cleaned.
Sometimes the fuel vendors pumps can deliver fuel at a rate that many boats cannot deal with. Most vendors can turn it down. If the nozzle barely fits in your tank fill be suspicious.
The ones with a nozzle about the size of a standard car fillup can't flow enough fuel to cause a problem aboard most boats unless a problem above is present. They sure can be slow sometimes though.
High delivery rates can cause serious foaming inside the tank which could cover the vent and help to cause a blowback. SOme additives may also make foaming worse.