I don't know what it is.......... but it sure aint right! I would pull the cowling and make sure it's not something rubbing under there...... also inspect the prop, but since it's new it should be under warranty I would be taking it back to dealer.........
What's the gear ratio for your engine? What's your current WOT speed and rpm? Unless it's way down there like 2.5 to 3:1 arena, a 14" dia 20" pitch is WAY too much. A prop like that would be used on a 150ish hp engine. A high pitched prop at idle rpms can cause a phenomenon referred to as "clutch dog rattle" which is the shift dog (in Mercury engines at least) vibrating back and forth on the prop shaft due to engine firing impulses vs a lot of resistance from the prop making pulsations. A 3 cyl engine can aggrivate it. I had it with my Merc 90 3 cyl high pitched SS prop. Use a different prop with a few inches less pitch and didn't hear it.
Thanks guys, my aluminum prop came in today. I installed it and went for a test run. 100% better. even gained 1mph. I went with a 14x19p. Runs 5300 at 37mph. Might go to a 17p later. . btw my lower gear ratio is 2.59.
