The vacuum seal may have failed in the tap or the owner may simply have not liked petrol taps that couldn't be manually turned off. If the vacuum seals fail and your float needles aren't sealing properly you can end up with a crankcase fuel of fuel. You can pull the plug, re-attach the hose and see if it still works, or unscrew the tap unit from the tank and have a look at the innards. The old 3 position vacuum taps had 'On', 'Prime' and 'Reserve' - how is the fuel being turned off now - is it flowing only when the tap is on 'Prime' or when on 'On' or 'Prime'? If there is no shut-off (ie, it flows in the 'On' position) then the tap needs to be replaced ASAP as it is faulty.
Using normal fuel lines will not have any effect on the bike at all as it is the original spec.
If you have a look at the pic of mine in your other post you will see that it has clear fuel lines; some of us like to see there is fuel going into the carbs.