Adjusting Trim Position Gauge

I just bought a 2002 Skeeter Bass boat with a Yamaha 130 V4 Engine. The trim position gauge on the dash works, but it doesn't show the correct engine position. Can someone tell me where/how to correct this problem?

There should be a rheostat on the mounting bracket of the mtor with a set screw. Put a level in the floor of the boat and get it center bubble using the trailer jack. Then set the level on the flywheel of the motor and trim till it is center bubble. Turn the key on and loosen the set screw on the rheostat and turn the housing till the trim guage reads staight up and down. Tighten set screw.
A v-hull boat "normally" likes to run 5-7 degrees up. If you have a degree wheel, set it on the floor and use the trailer jack to get it in position to read 7*. Use the level to set the motor back at center bubble. This should be the "optimum" trim for running flat out. Use a paint marker ot liquid paper to mark the trim gauge. Makes driving that much easier.