150cc gy6 won't start

[scootie101]

hi all I'm new here read a lot of good stuff on this forum, I used a manual off this site to do an engine rebuild(heat seized piston rings) so I rebuilt my engine did the timing started it up ran for 5 seconds then died, after that it just wouldn't start so I put another carb on tried starting it up nothing, checked the engine seems I'm leaking air past my rings.I can hear a squealing sound at compression stroke, rings are still good so yea I'm stumped .what's the cause of this and how can I fix it.also could this slight air leak cause my scooter not to start.thanks in advance.