aqua lark

hello im new to this site i have recentley bought an 84 aqua lark it came through with a 25 hp on it and i put a jack plate and a yamaha 40 hp on it with a 16 pitch now i cant get the boat to plane the guy who owned it before me had an evenrude 40 with a 19pitch and the boat went 52 i cant even get it to plane not sure what would be wrong

 

I suppose that you already have tried different trim angles.
Your prop's pitch is less than before. This can be one reason.
One other reason is weight or weight trim issues.

 

ok step one !,you need to check the motor set up of the boat is the first thing !,
Why have you got a jacking plate ?? do you understand what the jacking plate is for ?? is it push button adjustable or a manual adjustment??
how far is the motor back from the transom of the boat ??
To start with the Underside of the plate over the propeller needs to be about 5 to 6 mm above the line of the bottom of the hull . lay a straight edge along the bottom alongside the lower unit of the out board !! the plate need to be directly inline . do you have a trim gauge on the dash board ?? if so with a fine marker pen mark the glass so you know exactly where level is .
Like i said the underside of the plate over the propeller needs to be 5 to 6 mm above the level line . this is your starting point !! take the boat for a run use the trim button to raise of lower the nose of the boat . Trimangle is very sensitive on most boats . if you just hold your finger on the button you are never going to get it right . It need to be done gradually and slowly just a little at a time . you need to watch the spray coming out the side of the hull !! if the spray is coming out forward the nose should come up if its coming out quite a way back then the nose needs to go down a little . once you have found the optimum angle of trim again mark and take note of where it is on the gauge !! the rise and fall of the motor is dependant on how far back it is from the back of the transom.
Raising the motor to high the propeller will eventually loose its bite and all the reves in the world are going to do nothing . also if the motor is to high theres a chance the motor could over heat as the water pick up is not getting a continuous flow of water past it !!. all adjustments need to be done a little at a time .
If you set the tacho on the dash at 3500 rpms and then do your trim down the rpms drop as the hull is harder to push through the water ,!!!to far up same!, rpms drop , You need to find the one place where the rpms are at there highest . that is the best trim angle for that boat
now you know the trim angle you can raise your motor 5 mm at a time till you find the best place where there is no propeller airation taking place when you turn in either direction .