Need Prop Help... 140/Looper on a Bracket

[BigMike]

I have a 1979 V-20 ...I repowered it from an I/O to a Gil Bracket with floatation... Installed a 1988 Johnson 140HP VRO Looper .....It has a 13 1/4" X 17P aluminum prop on it, Cavitation plate is 2 1/2" above the bottom of hull... My V-20 is heavier than most with lots of gear and fishing equiptment and a hard top... Motor runs great but seems to have way to much prop on it the tach was broken. . I just installed a new tach.....I'm wondering if anyone can recomend a starting point for prop size I'm thinking 13 1/4 X 15p or even a 14p.....