If gas flows out of the carb when you turn the fuel petcock open sounds like you still have some carb issues.Sounds like maybe needle and seat is worn or stuck floats.Maybe its flooded and thats why your having trouble and why pouring gas down the cylinder didn,t help.

Is the plug wet with gas after trying to start it?

Also you really have to jump on the kicker on the 500,s.Get the kicker near the top of the stroke and kick it like your pissed off.Do a search hear and pretty sure some posts for starting technique on the 500,s.