Good evening everyone , I have a 72 commander 31 sedan with twin 350q engines , along with the original kohler Gen set that sits between them . The boat is rear heavy . I recently put the original size props on it , which per build sheet are 15”x17 pitch 3 blade bronze . When I hit half throttle it just goes nose up and chugs . On these old heavy gals , in order to get on plane do you have to go full throttle ? Or at least 3/4 throttle ? I’m used to smaller outboard powered boats , and lord knows I don’t want to hurt my baby, but man this thing is slow at a whopping 9 knots at what tachs say is 2100 rpm . The engines are both running well with no issues . It has a dual needle single face electric tach that’s probably 90s vintage so the old cable driven tachs are long gone . At a little over half throttle the tach is reading 4K rpm . That can’t be correct. The engines aren’t screaming . Any ideas ?
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Captain Mat ...... Purchase or borrow a digital dial back timing / tach gun and install on engine then run up to full throttle to verify rpm under way . Before that test remove throttle linkage at carb and CONFIRM you have correct full throttle at carb & helm match . You must also haul out your 31 and have the props removed and sent to a prop service shop that does Prop Scan or Hale MRI scanning to CONFIRM the props are correct pitch & dia . That is the only way to clear up your issues for prop size .You are going nowhere without a positive prop scan report at this time . Adding a 1 inch carb spacer which has been mentioned here will not help your boat to plane off issues . The best / only carb spacer for your engines is a 4 hole phenolic spacer 3/8 size and correct 4 hole base gasket from Dashman.net with no modifications needed for Pcv hose which is much better for heat soak reduction / performance . How did your 31 pass a survey / sea trial with these issues you are having ??? Do NOT replace carbs for any new carbs . Keep it simple .
Tim
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