Mounting long shaft motor on short transom

[whj812]

I am still new to boating. I bought a used 15HP mercury for my modified jon boat. My boat has a 15 inch transom, and I really needed a short shaft engine, but couldnt find one at the right price. I am purchasing a transom elevator for my boat so that the motor can be properly mounted, and will perform right.

I mounted the longshaft on today, to test the motor out. The motor runs great throttles up really nice and seems like it would have alot of power for my little boat. BUT when in gear I try and throttle the engine up and it gets to a certain speed and it feels like the motor quits pushing the boat. Sounds like the prop isnt even engaged, and revs really high.

Is this normal for a longshaft motor that is mounted on a 15 in transom? Is the drag that is being created by the plate being so low in the water causing this reaction?

I guess....another question is.

Will I see a decrease in performance due to the transom elevator? The transom is 15 inches and the elevator will take it up another 5 to 20.

Im used to my old 18 hp evinrude that ran up the lake at a pretty good rate. I hope this one gets close to that speed.

[Catt]

Look at the cavitation plate on the motor and measure how far below/above the bottom of the boat it is.

[George Welcome]

Long shaft is looking for a 20" transom - you possibly have a spun hub.

[CGH]

 Is this normal for a longshaft motor that is mounted on a 15 in transom? Is the drag that is being created by the plate being so low in the water causing this reaction

Your mother has no idea as to what transom it is on.  All it does is burn fuel at an increasing speed as you apply the throtle

The purpose of the transom elevator is get the cavitation plate on the motor at the correct postition in relationship withe bottom of the boat.

U have some other issue with your motor.  

1. Check the high speed adjustment on the motor.

2. Make sure their is no fuel leaks in my fuel system (My 25 Evinrude did this to me once and it  

   puzzeled me to tears)

3. Chech your spark plugs and mak sure neithe is fouled.

4. Make sure your fuel bulb (that thing you squeeze to prime the carb) is holding pressure

[bassboy1]

Sounds like a spun hub is your problem.  Take the prop to a prop shop and either buy a new one, or get them to re hub it.  The long shaft will only put a bit more drag, so your top end won't be quite as high as it will otherwise.  And, some say it makes it a tad harder to steer at high speeds, but that won't happen till you get really high speeds that a 15 horse isn't gonna give you.  

Doesn't sound like any of the 4 things wrong that CGH mentioned, as you sayed the motor revs high, so it isn't bad fuel line, plugs, or the high speed adjuster.  Check your hub.

[whj812]

Thanks everyone.  Taking motor back to where I bought it.  The guy there said to take it and test it out, and if I find anything wrong take it to them.

Ill post what they are able to find.

[whj812]

I took the motor back this morning on the way into work.  The rep there was really surprised that I was having issues.  He said that he was going to have a tech look at the motor right away.  Hopefully I get it back this week or next......they looked pretty backed up.  

Will post after I find out what is going on.

[whj812]

Finally got the motor back on Friday.  Mounted the Transom elevator on the boat.  Took the boat out last evening, man it feels good.  The elevator too the transom height to 20.5 inches.  The motor performed great, ran it for about 2 miles down the lake, and fished some.  Ill post some pics and show off my beast.

[CGH]

So what did the shop say was wroung with your outboard

[whj812]

They said that the prop that was installed was not properly installed, and that it wasnt even for the motor.  The owner of the place apologized and had a prop ordered, and installed for me.  The transom elevator works really well.  It brings the motor right up to where it needs to be.  

I took it out the other day.  Smoooooth running motor!!!!