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New Suzuki DF9.9B Prop

M

MFall2767

New member
Just installed a brand new 9.9 on a 16' pontoon. Motor runs great, but I am getting a lot of shudder and noise at certain RPMs. I can work around it to some extent by altering the RPMs or slowly increasing/decreasing acceleration, but it's not right. It came with the 10x5 4 blade "high thrust" prop and it seems like the boat of course does not plane out, and as RPMs increase it is spinning out or cavitating maybe? Am I on the right track? Had an older Evinrude on it and never had this problem.
 
The motor is “shuddering and noise at certain RPMs” means your watching the motor vibrate? One would hope a brand new engine would purr with no vibration. Is the noise coming from the engine or are you hearing a vibration from something else? Is the motor clamped on tight? Sounds like your motor might not be low enough is all could think of that would cause it to over rev. If you still have the old Evinrude compare the distance from the clamp brackets to the centre of the prop
 
The motor runs smoot, and is clamped plus 4 bolts. The shudder feels more like the prop. You can feel it catch and smooth out, making me think maybe the prop pitch is off because of the pontoon. I thought about the height too, but was thinking it might be too low actually. Would that have the same symptoms?
 
Not a prop expert but I don’t think a too low prop would cause cavitation. A too low prop would cause performance issues and not allow the engine to hit Suzuki’s specifications revs at WOT. Give the dealer a call, they may have some ideas or let you try a different prop.
 
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