Tach innacurate all of a sudden. Why?

[180Fisherman]

Last weekend I took out the boat. I'm running a 2000 Johnson 115 V4. I opened her up as I often do at the beginning of a trip just to make sure things are running properly. According to the tach, she ran up over 7k RPMs. Normally I get right at 6k at WOT. Judging by the sound of things there was no way I was at 7k rpms and all day I felt like the tach was reading a bit high. Maybe 500-800 rpms high. What could cause this?

 

[jonesg]

Re: Tach innacurate all of a sudden. Why?

Among other things, prop hub could be starting to slip allowing engine to run faster than the prop turns.