If you do not get even a whiff of odor coming out of the mixer (what you may call a carb), the regulator might not be "passing any gas".
You can check to see if the engine really "wants" to start by spraying about a 2 second burst of spray carburetor cleaner into the mixer and then cranking the engine over.
If the engine then acts as if it wants to run (for about a couple seconds) each time you spray the cleaner in, you definitely have a fuel delivery issue.
If, however, the engine still does not try to "fire" on this alternate fuel source, you may have an ignition issue instead...................or "also".