i cant fill up my gas tank!

IMO a Smaller hole won't work. It seems like more Ventilation is required. I would personally try removing the Filler neck and installing a vent. It needs to be above where the Nozzle ends up(Somewhere near the top). Drill a hole and see if it fixes it. If it does then you could fab up a metal tube to direct vapour's straight down the tube to a rubber fuel hose. Just Thinking out loud but I don't see why it wouldn't work.