Hi Kingtoyota,
As far as the muffler pressure goes the engine has to be running to pressurize the fuel tank. Fuel tank position relative to the carburetor is important. The needle valve of the engine should be slightly above the center line of the fuel tank as viewed from the side. ( 1/8 to 3/16" roughly) Too low would make it hard for the carburetor to pull fuel into it and too high would tend to siphon or flood the engine. With the carburetor at full throttle and the throat blocked with your finger you should be able to "pull" fuel from the tank through the fuel hose into the carburetor by turning the prop with your hand (make sure the glow plug is NOT connected
) If no fuel will flow then you may have a gummed up needle valve or a loose carburetor that leaks air.
It would be very helpful if you could post a picture or two of the engine so tha we can see what version of carburetor/ engine you are dealing with. Some of the fox engines had some odd design carburetors and had their own method of setting them up.
Hope this helps and good luck.
Carlos G.