Welcome aboard.
With problems like this it's best to start with basics.
Assuming you have a portable tank, is the vent open? If the tank is built-in, try running with the filler cap open or off, the tank vent may be plugged.
Two more thing to look at; do a compression test and verify you have a good strong spark. A compression gauge can be borrowed for free after making a deposit, from many chain auto parts stores. They also have spark testers for around 10 bucks, which is a handy tool to keep in the tool box.
