OK I am thinking you guys are right about the false tach reading.

First off, I am trimming the drive out once the boat planes.
I do have another boat with a gps speedo that goes about 40, and my Scarab is easilly faster so I believe the ancient speedo to be at least close.Upon reviewing the previous owners service records ( I bought the boat 1 month ago) I noticed he replaced about 1 coil per year, since I have owned it it has got a new coil. I checked the wiring and found that the grey tach wire has been cut and spliced in the harness, havent traced it out yet but could be a part of the problem. Now, my next question....I know some of these engines use an inline resistor before the coil, but can't find anywhere what wire it would be on, I have 2 wires on the positive post and 3 on the negative. I can account for where all should go except the 3rd wire on the negative side, no idea what thats for. Anyone have any ideas what a 3rd negaive post wire would be doing or whether or not I should be using a resistor before the coil?

Thanks for all the replys btw, If your ever in Patuxent River area I owe you a beer!