Re: Build Number 3. Engine won't fire?
new parts doesn't always mean good parts.
it's possible that your float is stuck in the up position not allowing gas to flow into the float bowl.
the petcock could be plugged up with debris inside the tank.
pull the spark plug and verify that you have spark. sometimes you can have spark, but it won't be strong enough to fire the fuel.
shoot a tiny bit of starting fluid into the carb and see if it will fire.
if it fires, you have a fuel delivery problem, or possibly a bad spark plug.
if your using the stock china spark plug, throw it out and get an ngk.