Vacuum Advance sticking?

Domed pistons and a lot of overlap in the cam make it want a lot more initial timing than factory. What you need to do is re-curve the distributor so you can run a lot of initial, but not a lot of total advance. It may still ping, the domed pistons will hurt you as far as ping goes. you may be too lean at idle too, which would explain the rise in idle speed..Also, make sure you're not hitting anything linkage wise with the air cleaner (I'm assuming that's what you are referring to as a breather).