Johnson 225 how high or how low??

[shuckbo]

Hi , I'm fitting a 225 Johnson to an 18ft speed boat I was looking for some advice , Should the cavation plate be level with the bottom off the hull or should it be raised or lowered , Many thanks.

 

[Dhadley]

Re: Johnson 225 how high or how low??

Welcome!!<br /><br />Your final height (X dimension) is a marriage between your hull design, prop design, balance, set back (how much if any), intended use and gearcase shape among other things.<br /><br />It might help to know more about your hull design and intended use to start with.

 

[Silvertip]

Re: Johnson 225 how high or how low??

As Dhadley says -- where the engine should sit depends on the design of the hull. Since you said "speed boat" start with the motor so the upper mounting bolts are in the second moutning holes from the top of the transom bracket(considered mounting position #2). This should place the cavitation plate at or slightly above the bottom of the boat. If you run a four-blade cupped prop you may be able to go higher. Remember, you can go too high.

 

[shuckbo]

Re: Johnson 225 how high or how low??

Hi , Well thanks for the reply , first i need to take the engine off the boat because i need to do some work to it , the compression is very very low about 65psi on all cyl's , during the summer the oil injection unit failed and i didnt know until the engine stalled , the guy who owned the boat before me had disconnected the warning buzzer, this engine is a 1988 looper , the engine is still running , but its a nightmare to get started , when you get it up to temp its not too bad , but i have losted some power too , so over the next few weeks i'm going to do a complete rebuild , but i have loads off time its the winter over here in Ireland, i have another question too , the gearbox is not engaging in reverse at idle speed , its fine when you give it a quick burst off throtle in seems to drop in ok , has anyone come accross this problem , Steve

 

[Dhadley]

Re: Johnson 225 how high or how low??

Ah...so we do have a baseline. Its not that youre putting this motor on the boat for the first time and looking for a place to start. Youve already done that.<br /><br />We still need to know about all the things in my first post. Plus we need to know how it was set up before and how it ran then. This will be your baseline. From the baseline we can calculate slip % and go from there.