honda tach prob

i have a 2006 honda 135, the tachometer was working fine last year. now its reading way off (says around 5000 rpms when im only around 3000-3500). havent looked at it or tried anything yet, just wondering if someone could give me a good place to start or idea of what might be wrong.

pretty simple setup
power
signal
ground
or the tach itself

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