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[jamalloco]

New Suzuki 300 HP,and new Prop with 70hrs only and my Prop spun any idea why??

[Solarman]

spun prop

Throttling up on a mud bank/ sand bar might cause such a problem, but, if only in water, could be a bad prop, or an old rebuilt prop that looked new?
If still under warranty have dealer replace it. If you hit something in the water that caused the prop to break loose, there should be evidence of that/ bent or damaged blade on prop.
Good luck.
One other possibility, if you have excessive cavitation (lots of air across prop) while running, this could cause prop to get excessively hot, causing this same problem.