Two hypothesis:
Carburetor isn’t metering fuel. Disconnect the fuel line, drain the carburetor bowl, crank it over and see if it will fire on starter fluid
No compression. Remove spark plug, put thumb over plug hole, crank engine. Should feel strong suction / pressure. If you don’t, stick a pencil / piece of wire down the plug hole and bar the engine over, pencil / wire should move with piston, if it doesn’t think connecting rod / crank. If it does move remove the valve cover and observe the valve movement, may have something stuck (or in my case a stud holding the rocker arm had worked loose, causing the exhaust valve to remain open).