Cant get boat on plane, 40 HP wont go faster than 14 mph

Joined
Aug 2, 2015
Messages
5
I have an 16ft aluminum boat with an 40 hp Nissan on it. cranks and sounds good. I am unable to get it on plane. wide open throttle it will only go 14 mph. motors sounds like it wants to go but it just doesnt go. sounds like at any second it would t take off. I put new plugs, new fuel tank new bulb and hoses.carb is newly replaced. maybe a different prop would help? it has an 11.4x12x3 on it now. I am confused why it seems like its plowing through water instead of picking up speed and getting on plane.

any help would be greatly appreciated. I am at total loss and hoping someone can help!
 

Sea Rider

Supreme Mariner
Joined
Sep 20, 2008
Messages
12,345
Has the engine received maintenance recently. Does carb opens all the way when at full throttle ? How old is that prop ? Probably you have a prop on its way to become completely spun, assume that's the original factory delivered prop, right ?

Happy Boating
 
Joined
Aug 2, 2015
Messages
5
the motor was serviced regularly according to previous owner. it appears carbs open and linkage is working properly. I believe its the factory prop. I pulled the prop and saw fishing line wrapped around it. the splines were kinda dry. I just done know where to go from this point.
 

pro-crastinator

Chief Petty Officer
Joined
Dec 12, 2013
Messages
453
Is this a "new to you" boat and motor?
Have you fiddled with trimming the motor?
How much does the boat weigh - loaded? (Is it just you and your daughter? - (envy, cant get mine out there!))
Tiller steer motor?
 

Sea Rider

Supreme Mariner
Joined
Sep 20, 2008
Messages
12,345
14 MPH is extremely poor for a 40 HP engine, my 18 does 20 easily. To begin troubleshooting will need to perform a spun test, remove prop, mark with a white marker the center hub area with a straight line, place prop back.

Go for a wot spin you alone for some minutes with engine trimmed for boat to ride parallel to water surface when on plane, remove prop, check marked line, if has moved from its original marked position you have a spun prop. Buy same new. Factory delivered props performs very well on light to medium light applications. Was that prop tached at wot before failing ?

Happy Boating
 

MattFL

Master Chief Petty Officer
Joined
Oct 20, 2010
Messages
827
If the boat is squatting, bow high, then put some weight up front. Have a buddy sit up there or put a bucket or two of water up there. Also make sure the engine isn't trimmed too high. I'm guessing you've got a really light boat with most of the weight in the stern. If the weight is balanced then this won't help..
 
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