Sounds like a fuel tank problem. At least from the discription that you give. I agree with your dad. Make the holes thru the firewall a little larger. Is there foam between the tank and firewall inside? Are the fuel line set up as per the instuctions? Sometimes muffler pressure can cause air bubbles if the line into the tank is wrong.
You may also have a vibration problem. What prop and spinner are you using ? Have you checked them for good balance.
I'm sure you will get some other suggestions as well.
Let us know what you find.