2011 merc 25hp jet motor performance

[cgrif]

Hello all,

This is my first post. I have the above motor. It is on a Lund 1648m Jon. The motor runs like a top, but dispite the promises of the mercury sales team, I feel the motor is not quite enough to push this boat on a river (at least not to the performance I feel I need). I have spent a considerable amount of time lining up the motor height on the jack plate, played with weight distribution, but all in all, I have exhausted all the limited tricks I have. With my 220lb body on the tiller, the boat gets to plane relatively fast. With 2 adults and 2 small children(total weight=475llbs) the boat wont get to plane and labours a fair bit. My goal is to have 2 adults and some camping gear (evenly distributed weight 450-500lbs) hit plane. Am I asking too much of the motor? Are there performance upgrades that can be made to achieve what I want? The boat is only rated for a max power of 35hp. This is the boat I want to use for my purposes, so changing the boat out is not really an option for me. I really like the boat/motor combo that I have. If I could only get a little more performance out of this set up, I know that I would be happy, but right now I know that the motor is not quite enough for what I want to do with it.
I am interested in hearing any and all suggestions that could lead to a solution. I have done a lot of "asking around", but with a forum of this size, I am hoping there will be that one or two suggestions that will help.

PS. I have a 2011 Merc 30hp prop engine, and it drives this boat, with the above load, with ease. This is leading me to believe that just a little more performance (5hp or so) will cure my problems. Just a thought.

Thanks in advance to all, and I look forward to hearing from you folks.

 

[canoemang]

Re: 2011 merc 25hp jet motor performance

If it is a 25 hp prop with a jet foot on it you only are at 17.5 HP at the pump. You are asking to much of that motor.

The weight chart over at outboardjets.com shows a 17.5 hp jet can at max handle 600 or 700 lbs.. gross, so thats including boat,gear and people.

If the boat is rated for 35 HP, you could find a 50 Hp Jet (35 hp at foot) and it would still be at the rated Hp and scoot that boat through skinny water. With a jet overkill, is better and weight is the worst thing for performance with them.

 

[cgrif]

Re: 2011 merc 25hp jet motor performance

Thanks for the response. Just to restate though, it is a new merc. The power end is actually a 40hp and is rated at 25hp at the foot. As I stated in the original post, I think I am lacking only 5-10 horse to make this package do what I want. The 25hp rating is given by engineers at Mercury, so that being said I am treating the 25hp @ the foot as a close estimate only. The one thing that I know for sure is, it is not enough to hit the rivers. Please keep any feed back coming, I am sure there is an answer.

If it is a 25 hp prop with a jet foot on it you only are at 17.5 HP at the pump. You are asking to much of that motor.

The weight chart over at outboardjets.com shows a 17.5 hp jet can at max handle 600 or 700 lbs.. gross, so thats including boat,gear and people.

If the boat is rated for 35 HP, you could find a 50 Hp Jet (35 hp at foot) and it would still be at the rated Hp and scoot that boat through skinny water. With a jet overkill, is better and weight is the worst thing for performance with them.

 

[canoemang]

Re: 2011 merc 25hp jet motor performance

I didn't know it was a 40/28.. That is odd it wont get you up on plane with the weight you've said. I have a buddy i run my jet rig with with who had a Lowe 1648 with a Yamaha 40/28 jet, i have seen him get 4 adults on plane with no problems. He recently went with a 1652 Alweld and planes faster time/slower speed due to wider boat..

Are you cavitating during take off?

Is your impeller shimmed to high?

Have you tried swapping battery,gear,gas tank around?

Is the Lead of the jet shoe in line with the bottom of the hull?

 

[Mi duckdown]

Re: 2011 merc 25hp jet motor performance

Pics of your set @ transom up would help alot. You should have No problem with that size motor and that boat. PICS.
How far back is the motor the motor from the transom with the jackplate?

 

[Mi duckdown]

Re: 2011 merc 25hp jet motor performance

Is this motor a 4 stroke???

 

[cgrif]

Re: 2011 merc 25hp jet motor performance

Is this motor a 4 stroke???

thanks for getting back to me. to answer the questions, the motor is on a jack plate and the front of foot or intake is 6 inches from the transom. the foot intake is flush with bottom of the boat or 1/4" higher. I have an adjustable jack plate so playing with that has been done. It is a 4 stroke 40/25 merc, 2011. It is electric start but I pull start to minimize weight. I have not moved the fuel tank around but I have had the other passengers change positioning while experimenting. I do not hear cavitation unless I am in choppy water or turning very sharply while on plane. Both instances where I have heard cavitation was while on plane. the only time I have heard it skip or cavitate has been in choppy water. Unfortunately I cant get you a picture of the set up because I have stored it for the winter. I have taken to the motor and boat to the local Mercury dealer/service shop. They have adjusted the impeller. The owner suspected that the impeller was originally allowing too much water intake. He removed a shim. It did help me get on plane quicker but the previously stated issues still remain.

I have one idea I want to run by you. Have you ever heard of a ray fin or sting ray like fin being ran on motors like this? I know they are common on prop engines, and guys that have them swear by them. I do not know of any aftermarket sting rays being built, but I have access to nylon sheeting and I am a bit of a fabricator. I will measure sting rays that are put on prop engines and try to mimic that size, shape, pitch and width. Do you think it is worth a shot? I have measured my motor set up and I am confident that I can make one quite easily.

Thanks again for the input.

 

[Mi duckdown]

Re: 2011 merc 25hp jet motor performance

The Impelar to sleve is 30 thousands I Think Don'thave manual handy and don't quote me on that.
Fin ain't going to work.
Goggle San Leandro Jets California. That is who makes them. Not 800 Number. But you will get All info you need.
Cgif. I run 16' semi v with a 25/20 jet tiller, with 2 people at 390 lbs. and 100 pound Lab and 50 decoys in the front of boat. but i'm planning.