There were several posts on the old Parker forum about this problem.
I also posted a similar topic here:
http://classicparker.com/phpBB2/viewtop ... highlight=
FWIW, the tank vent I had on my 1999 was a Perko that had the black plastic cap on the outside of the hull, with a 90* fitting to the vent hose inside the hull. Once you unscrew the cap, you will see that there is a mesh screen within the hose, and mine was pretty gunked up and corroded, which I'm sure impeded the flow of air, and caused the fuel fill to 'burp' gasoline if it was pumped in too quickly.
The replacement parts are very inexpensive and easy to install, so I just replaced it with a new one. Haven't splashed the boat yet, so not sure if it fixes the problem 100% or not.
You might be able to get away with removing the cap and cleaning out the screen, depending on how much corrosion there is.
If you don't replace it with the same model Perko vent and choose to go with another vent with a 90* fitting, make sure that you get one that will have the vents installed in the correct position when actually installed in your boat.
My boat had the 90* vent fitting pointed UP to an anti-siphon loop in the vent hose. A couple of the other 90* vents I looked at were designed for the hose to point DOWN. So if installed in my boat, the vents on the outside of the hull would have been pointing up and would catch rainwater, etc. Another model had some built-in baffles and such to keep sea water out, but again, these were designed to point DOWN and wouldn't work correctly if installed upside down.
Hope this helps..