With a bubble primer the line from the fuel tank which is the suction one with the fuel filter on the end goes to the inlet fitting usually the one with a slightly larger diameter on the carburator(the pump diaphram side), the smaller outlet from the metering side of the carburator goes to the suction side of the primer bubble then a line goes back to the fuel tank from the other side of the primer bubble.Priming the carburator and returning excess fuel back to the tank.I hope this is of help
Dave Fix, May 2011