Custom Jet Boat Problem

Hello, I am not sure where to post this question. I restored a 1960 Arkansas Traveler 14' and installed the engine and pump from a 1995 Seadoo GTX
70hp. The boat runs great and gets on plane no problem. Once on plane, it wants to pull hard to the left and I can't correct it with steering, I have to go back to idle speed. Steering control is fine at idle. Could this be a problem with the hull shape?
Thanks
Duane

 

I know absolutely nothing about this, so I am going to have a wild stab in the dark. Could they new engine be rotating in the opposite direction from the original and the hull shape was made to compensate for the original rotation?

Poida

 

To be more specific on the hull, I used a sawz-all to cut the hull of the jet ski (leaving the engine and pump mounted) I then placed it into the opening I cut in the hull of the boat and used stringers to fiberglass it in place.
The hull of the boat has what looks like a 2" diameter pipe running down the center, flaring out as it gets to the stern. The last 2' of the hull is almost flat.
I had to cut out about 6" of that "pipe" to mount the jet ski hull. I flared it out
using bondo.

 

Check symmetry on the hull. Also, is the helm seat to port or starboard? Does the boat have chines? On a small boat like this, if the steering station is to starboard, then the boat is going to go to port when it is going fast.

 

The hull looks symmetrical, of course my bondo work is not perfect. There are no chines. The helm seat is starboard. I am thinking that the engine/pump may be out of alignment with the hull. I am going to have someone film the boat on plane to maybe reveal some clues.
I may have to look into some type of adjustable rudder or trim tabs.

 

Try running the boat at speed with you sitting on centerline or even as far to port as you can. If it this cures it, then you can add a small (1/4" to 5/16" max high by about 4" wide) wedge to the starboard side of the bottom oat the transom.
Are there any protrusions from the bottom of the boat on the port side? A high speed water intake strainer? It is amazing how a small amount of area will affect things.