Mercury 2.5HP Outboard Not Moving Boat?

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Bburdette

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May 12, 2025
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I bought this 2010 Mercury 2.5HP, 4-Stroke (Short Shaft) motor last week to put on my new Bass Pro Pond Prowler 10 (10' 2"). When I got there to buy the motor, I was surprised how good the condition was. He ran it for me in a water bucket and everything appeared to be working as it should. This past weekend I took out my new Pond Prowler and the new used motor. Got it put on the boat and into the water. It started up, first pull. Let it idle a bit with no problems. But when I put it in forward and gave it the some throttle, the boat just sit there. I gave it more and more throttle but the boat basically barley moved. What could possibly be wrong? I know absolutely nothing about a boat motor. But when I got home, I put the motor on my stand and put the drive in neutral. Turning it with my hand, the motor prop turned freely. Then I put it in forward and the prop turned a little a little then stopped. It done the same the other way. Leaving it in forward I pulled on the pull cord slowly and the propeller starting turning as I pulled it. As far as I can tell it is working as it should. Also the motor is setting all the way vertical. What could be the problem? Please help. Thanks for any response.
 
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Bburdette

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Joined
May 12, 2025
Messages
7
I bought this 2010 Mercury 2.5HP, 4-Stroke (Short Shaft) motor last week to put on my new Bass Pro Pond Prowler 10 (10' 2"). When I got there to buy the motor, I was surprised how good the condition was. He ran it for me in a water bucket and everything appeared to be working as it should. This past weekend I took out my new Pond Prowler and the new used motor. Got it put on the boat and into the water. It started up, first pull. Let it idle a bit with no problems. But when I put it in forward and gave it the some throttle, the boat just sit there. I gave it more and more throttle but the boat basically barley moved. What could possibly be wrong? I know absolutely nothing about a boat motor. But when I got home, I put the motor on my stand and put the drive in neutral. Turning it with my hand, the motor prop turned freely. Then I put it in forward and the prop turned a little a little then stopped. It done the same the other way. Leaving it in forward I pulled on the pull cord slowly and the propeller starting turning as I pulled it. As far as I can tell it is working as it should. Also the motor is setting all the way vertical. What could be the problem? Please help. Thanks for any response.
 
Scott Danforth

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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check for a spun prop hub.

I merged your threads. please do not create more than one thread on the same topic
 
Scott Danforth

Scott Danforth

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take a sharpie marker and draw a line across the prop, and the prop shaft. run the motor. if the line changes, you have a spun prop hub and simply need a new prop
 
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Bburdette

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Sorry for being stupid, but draw a line across the propeller and continue to draw the line across the shaft. Start the motor in Neutral, and it the drawn line on the propeller and shaft is not in alignment after running the motor, then I need to buy a new propeller? Is this correct?
 
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Bburdette

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I took off the propeller and found this.
 

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Texasmark

Texasmark

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Joined
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14,786
Is water moving out from behind the engine when you apply throttle?
No, then prop isn't being driven as suggested above or engine isn't shifting into F gear like you are telling it.
Yes, 15" lower unit on a 20" transom would be a problem. Need new water in front of the prop to get propulsion. If engine is too short, the boat blocks the needed water for proper propulsion.
 
A

airshot

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5,446
Pull off your spark plug wire, then remove your spark plug, then put motor in gear and try turning the prop shaft. If needed, put a pin or something thru the shear pin hole to aid in turning. If the engine turns over when doing so, your gear shift is working and just need a new prop, shear pin and cotter key. If the engine does not turn over when turning the prop shaft, then you have a shifter issue.
 
flashback

flashback

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3,991
looks like the drive pin has sheered and someone removed the pieces, The prop hub is obviously damaged but may still work.
 
M

Mc Tool

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Aug 7, 2024
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373
Or someone has put a split pin in the drive pin hole and it has folded up under load
 
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Mc Tool

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bigblocksarefun said:
Not exactly....I know they commonly get used interchangeably but there is an actual difference. These guys do a much better job explaining it (other than metallurgy) than I would: https://www.reidsupply.com/en-us/industry-news/cotter-pin-vs-split-pin
Click to expand...
Yeah ,I get that , split pin is for retaining nuts etc not for transfering torque . A cotter pin ,in this instance transfers the drive to the prop and is a solid pin , maybe brass with a plastic prop, but a lot more substantial than a split pin .
Possibly someone ,for whatever reason has fitted a split pin instead of a cotter pin which has failed, got bent up under load or was bent to fit in the recess in the prop , and just wasnt up to transfering the torque , shaft turns inside prop and damaged the prop .
Maybe 🙂
 
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