[bad_the_ba]

Brand new to these forums, I thought I'd give this a shot and see if anyone has run into the switch I will be attempting. I bought a 1979 Evinrude 85HP to replace a Force 90 with top end problems. This is on a 19' Spectrum aluminum boat. The Evinrude does not have power trim and tilt like the Force did, but I also ran into another problem. I had a shop make the switch for me, since I had bought the motor from them off an auction acquired boat. The transom on my Spectrum aluminum boat dips down appr. 4" in the center, about 18" wide where the motor mounts, which worked well with the original motor. However, the mounting equipment for the Evinrude causes the steering cable to come through where the motor pivots, which happens to be directly overtop of the raised part of the transom on either side of the motor. On the old motor, the cable fell in front of the transom, and did not block the motor from being lowered to it's proper height. At this point, with the Evinrude installed and the steering cable coming across and resting on the top of the transom sides (which, as stated before, are raised above the center part of the transom where the motor mounts), the prop is too high in the water, and I experience a loss of thrust when accelerating quickly, going above 27-30mph, and when turning sharply. I had the same shop that installed the motor test drive it, and they have told me that it looks as if it is 3/4 of an inch too high, and that air is able to get to the prop and cause what seems like cavitation. If what they are telling me is true, then the possible solutions are to cut the transom to accommodate for the steering, replace some of the mounting hardware to allow the steering to fall in front of the transom like the original motor did, or go to some type of lesser quality steering system which will not interfere with the optimal mounting height. The mounting holes will allow for moving the motor down, which is desired, but not up. At this point, I have a junk 60HP OMC motor in my possession (unidentified year) which has the mounting hardware I would need, with the pivot and steering shaft coming through in front of the transom. (the transom on my boat is 2.25" thick, the nuts on the outsides of the mounting plates fall in at over 2.5" forward from the back of the transom.) All the measurements match up for mounting bolts, shaft length, steering, etc. The junk motor I am using for replacement parts was used in salt water, but it looks like it can be cleaned up well, and it has working power trim and tilt.
My first question is, has anyone performed this same kind of conversion to accommodate for a specific transom shape and steering cable position.
My second question is, what are the chances that the motor height is not a big factor in my case, and that the propeller is in deed cavitating. If I try to accelerate quickly from sitting still, the propeller will spin rapidly with very little thrust, and sounds like it is coming out of the water. The same sounds and feel come when pulling a single skier or a tube at certain speeds, or when taking sharp turns at 20-25mph or over. If I slowly throttle up, and then cruise fairly straight at under 30mph, I do not run into these issues, but it makes it impossible to pull a tuber or skier, which is an important goal.

Some side notes that may be important to someone:
1. At one time I had my propeller serviced, and took a fishing trip with a loaner propeller of a sharper pitch. I believe I had faster acceleration with the other prop, but the issue I am addressing here was no different.
2. The starting weight of the boat may be higher than it should be, as I am unsure at this point if the foam in the back of the boat is holding water, It is an 8 passenger boat, and it does this "cavitating" whether I am alone, or have 4 or 5 average sized people in the boat. Before I purchased the boat, it had sat in a yard with a torn cover for almost 4 years, and small areas of the floor are starting to rot. I replaced the entire bow flooring, which is raised up from the rest of the floor, with 3/4" Starboard, but the weight difference between that and the original flooring is negligible. When I had the bow flooring torn up, the foam near the front of the hull that I exposed was dry, but it is also higher than the rest of the floor.
3. The boat is tagged with a maximum motor HP capacity of 125HP. However, I doubt the motor is underpowered for this length and size of boat. I have been told that an 85HP Evinrude is better than any HP Force that would have been original on this boat, and it came with a 90HP Force. I do not feel like I have gone backward any.

At this point, if I can get the rest of the salt water motor apart, the plan is to go ahead with the switch. If this works, I will at least have a trim and tilt assembly at no additional cost, and will be able to adjust the mounting height. I will post pictures if needed, and if the switch is successful, I will report as to whether there is any change in the problems I am experiencing. Thanks in advance for any help or advice.

[tashasdaddy]

i had a 90 johnson on a 18' spectrum. was almost overpowered. would run 48mph. and would get squirrelly.

[bad_the_ba]

so are you indicating that the motor indeed is cavitating? Is this a problem remedied by changing propeller pitch? It tends to give similar syptoms at many different throttle positions, depending on whether the boat is already moving or not, so I don't know that it is "overpowered" as you say. If I can break free the parts of the salt water motor, I will know soon enough if changing the height will help.