The idle mixture has almost nothing to do with starting it. The beginning point for the screw is 1 1/2 turns open. You need full choke and some throttle to start it.
When it is trying to start you will hear the starter start turning a lot faster. I would try varying the timing a little each way. Too much advance will make it stop dead when trying to start it.
The float level should be set to spec which is something like 1 9/32" if I remember correctly.
