There are actually quite a few reasons you have no pressure. Of course they all have to do with an air leak or blockage.

Front bearing on the engine is leaking.
Engine case has a crack somewhere.
Fuel tank has a split at the seam, or a crack, or a hole
Pipe has a clog in the pressure nipple
Pressure nipple on fuel tank is clogged.
Pressure line has a hole in it.
Cooling head and button are loose
Carb is not tight.
Pinch bolt leaking.
Hole in the carb slide boot.
Fuel line is clogged or leaking.
Carb nipple is blocked.

There may be more but I'm tired of typing.

Start going through the list one by one. Good luck.