if the tank is good and you are getting air right from the tank you have a pressure problem from the tank to the pipe. if you are using 3 feet of fuel tubing the mtor could draw more then your sending out of the tank. if the pipe nipple is cloged you will have low pressure. make sure the pressure line is good,i always use 9 1/2". and the most common one is a motor with low compression will have a hard time building tank pressure which will give you the air bubbles and the flame outs.