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Is anyone running an older 17' Montauk with a Yamaha F90 sour stroke? I am running this on a 1986 and I have been having handling issues since the engine swap. If you have this set up I would love to talk about how you are set up and how you like it.
I posted on THT and people suggested posting here. I still need to get the boat pulled out of the garage for the season to check the height of the cavitation plate and to figure out what prop is on it (it was the SS one that came to us from the installer). The motor was professionally installed, it is mounted using the second set of holes down from the top, my recollection is that the cavitation plate is "about" at the height of the keel (it was professionally installed and I have looked at the height in the past...however, if you ask if it is 1-2" above or below the keel I can not give an absolute answer right now) and, when I looked at the trim tab, it was set off only about 10-15 degrees to the right (when viewed from behind). So the set-up seems "reasonable" but, based on handing, something is clearly wrong.
Once on plane, with a balanced helm, at any given RPM if you trim up 1/2 second it pulls VERY HARD one way and if you trim down 1/2 second it pulls VERY HARD the other. Also, by changing even a few hundred RPMs (up or down), the helm pulls VERY HARD (I do not recall if speeding up pulls one way and slowing down pulls the other or not).
I am reluctant to simply try to mask the problem by increasing the anti-feedback in some way (if that is even possible) since I will 1) be unaware if the engine is really pulling in a direction and under tremendous stress and 2) if it fails it could go VERY bad VERY fast.
i am putting a yamaha 90f on my 1978 montauk this week, i also am having it done by a boat mechanic, i will let you know how it goes and i will be curious on how you solve your problem.
I have a 1979 Montauk with a 2004 90 HP Yamaha 4 stroke.
It replaced a 90 HP 2 stroke Johnson.
My trim tab is 1/4" to the the right of center looking forward from behind it. The mounting is 2" below the transom cutout which is where the top mounting bolt is, which is the second one down from the the top. Then the second bolt is the 4th hole down or 4" from the top of the transom. The engine mounting bracket has 4 holes so I am using the 2nd and 4th from the top. The engine is centered on the transom.
I have no cavitation or steering problems, get about 5 miles per gallon. It is a great motor and except for the added weight which lowers the stern a little has no problems. I would recommend this setup to any montauk owner. I have the Doel-Fins and they are level with the bottom of the boat. This height does not give me any problems with the motor up or down for shallow or deep water.
I have a 1987 Montauk with a 2005 F90 Yamaha and 8HP high thrust kicker. Both motors are four strokes. When these were originally installed the boat pulled to the right. I noticed that the added weight caused the swim step to drag even when on plane. I raised the swim step up about 2 inches and the handling issues stopped. I have the trim tab set about 1/4 inch to the right.
