1998 mercury 25hp bigfoot 4 stroke

by Stephen Stracener
(Orlando Florida USA)

It is on a 16 ft crest pontoon boat. 10 5/8 by 11 pitch prop. WOT is 5300 RPM. I switched to a 10 5/8 by 12 pitch prop RPM dropped to
4800 and engine begins to missfire.I know this by feel and watching the tach jump. Then It will begin to lose power and begin bogging down. I switched back to old prop and the problem seems to go away almost. Has a brand new OEM Carburetor and new plugs. Has anyone experienced this? I'm new to boating and suggestions would be most appreciated.