"Blow out" engine

My engine broke the piston and the connecting pin rod , it is a 1985 Vespa PX150E with Polini kit 177cc, Crankcases cuts, Malossi Reed Valve Kit PHB 30 mm, Full circle Shaft, HP4 Flywheel Performance Stainless Steel exhaust, 21 cog gears. Any idea why it happens?[:dance3:]