RPM tach issue

My 2001 225 yamaha has run perfectly until after I hit something on bottom while idling into a shallow slip. The hit caused the engine to shut off. It started up fine with no visible damage anywhere - prop and surounding area look fine.

Ever since then, when up on plane and running at 4,000 rpms , the rpm gauge intermittently runs up to 5,000 or so then back down to 4,000. There is no engine sound or speed change during this rpm run up. Engine continues to run smooth at the same mph speed.

I am not convinced that the hit in the slip incident and this rpm issue are related but this problem seemed to start right after. Any ideas would be appreciated. Thanks, Tom

[boats.net]

Mark your prop to check for a slipping hub. Scribe a line across porp washer and hub of prop, take boat out run it then look at line to see if still lined up. If misaligned then hub needs to be replaced in prop.