Just what was said above about removing the fuel line first.

This is to see if it can run first. If it will not fire adding fuel to the plug hole then you are either flooded or still missing one of the three key components. Proper fuel/air mix, enough compression and a properly timed spark you must have.

Disconnecting the fuel line will ensure the carb isn't introducing an over rich condition that floods the engine.

With fuel feed line off the carb add fuel to the plug hole. Hold the throttle wide open and pull. If it won't start and burn off the fuel you added then you have narrowed it down to improperly timed spark also as already mentioned or just not enough compression.

Don't waste time just now searching for a vacuum leak any where as it will still pop and try to run even with a very large leak they just don't pull fuel well through the carb at pullstart speeds even when fully choked.

Did you put the piston in the correct direction?