Have a 2005 merc 2.5 that is used as a trolling motor on 16 ft with 40 merc as main motor, the 2.5 at lowest setting moves the boat faster than I want for trolling, have talked to merc and there is not a prop avalible with a lower pich ( prop is 7 3/8 x 6 ). There is one ajustment on the carb...