Ive had good luck with tygon fuel tubing for the vent lines and fuel supply lines from the pump to the carbs. The stock stuff is metric, want to say 5mm from memory but thats just a guess... 3/16 sounds right for imperial. The aftermarket stuff is thinner walled so the stock line clamps usually fit too loose. That tygon stuff fits snug as well and is a yellow/green color. Seems to hold up reasonably well.