Won't start

The sticker on the fender says to set idle at 750 in neutral. It was running a little fast, at 840, so I turned out the idle screw by about half a turn and it settled around 750. Do you recommend advancing the timing some more until it pings? It has pretty good pick up already, but I could try advancing it some more. I have another 15 degrees of advance before I need to shift more than just the rotation of the dizzy. I based the timing on the mark on the balancer - engine was rebuild about 30-40k miles ago, if that is any indicator that it hasn't shifted too much in that time.

-JP