lol, that's plug glazing. if you throw an igniter on them, they'll spark down allong the insulator, insteard of across the gap. what causes it is deposits, like separated oil, or unburned leftovers form the high octane fuel. when you pull hard, it heats them up quickly and glazes the deposits to a conductive coating. it can also happen from the wrong heat range. either you were too rich on the bottom to heat them up and keep them hot, or you just need less octane. rule of thumb is 165psi and +4 is safe for pump, but it really depends on cr/elevation. what setup, bore, porting, and dome size are/were you running? pipes, too.