Gas leaking from air filter

As Red mentions above:
- needle jet upside down or missing
- stuck float, float valve, or debris lodged between the float valve.

Reversion will generally cause deceleration pop or crackle, and in real bad cases cause a backfire back through the carburetor. The problem you describe sounds more like fuel that is flowing uncontrollably by way of a worn float needle valve. They can look perfectly fine but when the rubber tip becomes slightly worn or hardened over time they will leak fuel into the bowl and flood the air cleaner element. What is worse is allowing fuel to wash down your cylinders after you stop, which in turn dilutes your oil and increases wear.

what kind of fuel petcock do you have, a gravity (pingle) or stock HD

stock hd takes vacuum to operate so when it's off, nothing flows
a pingle flows all the time.

Reason I ask is it sounds like a typical stuck float issue, fuel just doesn't
rise up out of a carb unless it's got somewhere to go, like water.

Fuel tank is above the carb, so fuel flows to the bowl, once the bowl is full
it's flowing out the carb into the engine or out the filter to the ground.

My guess is the floats not set properly and it's not closing fuel flow off