Yep.. Neutral wire. Check to see if it's plugged in, just in case.. Make sure it's not pinched, too..
After that, start with the simple stuff.. Kill switch, and anything else that you can see or touch..
After that, give a shout to Eagle Mike tomorrow, or tear it back apart to see if anything looks goofy.. In reality, unless the key didn't go into the correct location and fell out why putting the fly wheel on, it should run.
Also, check to see if your vacuum line is back on the petcock. Bypass the petcock with a soda bottle of gas and a fuel line directly to the carb to see if that's the issue..