Won't start unless I pour gas into the carburetor.

Basic answer: the float bowl isn't filling up.

The electrical system won't be addressed here and it’s assumed it is in working order.

With engine off look down the carburetor bore and pump the gas once. You should see a stream of fuel come out of the venturi.

To verify look down the bore and pump the gas once. You should see a squirt of gas go into the bore.

If you don’t see fuel spray into the bore:

If you do see a squirt of gas, move on to: