How much nitrous for a stock piston?
I'd rather go lean than rich. Lean, it will pop/backfire and shut off. Rich it will run til the ring lands/pistons come apart. Neither is a god situation.
The tunes in most kits are usually pig rich.
Try to figure a way to retard the timing when the juice is in use. You need to learn how to read plug really well when trying to tune for juice. Or get a wideband reader and learn to tune with that.
If you have too much timing, the electrodes usually start to burn up.