need help understanding whats happening

[Jasonsamko]

I have a tracker jon boat 1542. the boat calls for a short shaft up to 25 hp.
I got a 1978 johnson 6 hp short shaft from my buddy for free.

as the motor hits wide open (last 15% of throttle) all of a sudden the motor gets loud and losses momentum. its like the motor runs out of water to bite into.

Is there a way for me to fix this?
what is actually causing it?

the motor has a 3 blade prop with some edged dings but not horrible. the motor is mounted down as low as i can get it.

 

[steelespike]

Re: need help understanding whats happening

If the anti vent plate(just above the prop) is about even with the bottom of the transom it
sounds like spun hub. Remove the prop and put a water proof mark across the hub and body, run the boat and check the mark.If the line is broken you have a spun hub. While it can be repaired I think more cost effective to replace the prop.
However if you get it fixed and do some test runs get us the prop size, rpm and speed by gps we can help figure what prop will work best.
A Tinytach will work for the rpm.Some cells have a gps.
Then you could keep the old one for a spare.Is the Tracker a bare boat?If it has a floor and live well etc you will all most surely need a prop change. A gps speed will be a good start.

 

[saumon]

Re: need help understanding whats happening

Is the Tracker a bare boat?

Bare as it can be

 

[Jasonsamko]

Re: need help understanding whats happening

Yep the tracker is a 200 pound bare Jon boat.
I should of been more specific that I can run wide open for about 100 yards with no problembit then it feels like the prop is slipping and the motor gets loud like it isn't getting enough water.

 

[jestor68]

Re: need help understanding whats happening

What you may be experiencing is ventilation caused by that large keel creating turbulence right in front of the 1950's technology prop that's on your motor.

Solas recently started making available 2013 technology props for smaller motors like yours. Their 2011-083-08P 8 pitch prop should perform noticeably better than your old prop for $54.28.

Check the tilt pin setting on your motor and place the pin in the first hole nearest the transom. That places the prop a little lower in the water. That, plus a better performing "modern" propeller design should get you going.