engine set up question

[longshot]

I just got a 1650 Xpress jon boat and put a johnson 48spl on it. When I try to take off it will cavitate a little. When I run it above 2/3 throttle it will also gain no speed and start to make a different sound and sometimes cavitate. I have a 12.25 X 15 alum prop on the boat. The motor is all the way down on the boat and is all the way forward. What are your thoughts and ideas?<br /><br />thanks<br />longshot

 

[johndezman]

Re: engine set up question

really need more info like rpm, speed, etc. <br /><br />but in generalities....<br /><br />if there is no change in rpm with that much throttle movement the odds are that the motor has too much propeller and is not reaching its recommended operating range. get a tach, get some readings and adjust the pitch accordingly. a 1"<br />change usually will make a 200-300 rpm change (less pitch will increase rpm).<br /><br />by "all the way forward" i assume you mean the tilt pin is in the farthest forward position. most engine manual's indicate that the motor should be perpindicular (?) at speed. i doubt this is the case on the innermost pin position. using this position has the effect of lifting the transom and depressing the bow. while it doesn't sound like this combination is a real burner this will affect handling on plane.

 

[longshot]

Re: engine set up question

The engine has gas assist to help you lift it. I am running it as far down as it will go. I also have no way to tell the rpm or the speed. The boat is about 1100 lbs total including people if that would make a difference.<br /><br />thanks<br />longshot

 

[mrc]

Re: engine set up question

Is the prop damaged?<br /><br />Is it possible that the prop hub is slipping rather than cavitating?<br /><br />Mike

 

[longshot]

Re: engine set up question

THe prop is new......<br /><br />longshot

 

[longshot]

Re: engine set up question

 

[Dhadley]

Re: engine set up question

The prop is new!! Did it do this with the old prop?<br /><br />Where's the anti ventalation (cavitation) plate in relation to the bottom?<br /><br />More info please!!

 

[longshot]

Re: engine set up question

The prop is new, but the engine is a 1996. I just got the engine about 5 days ago. When it is is on plane I can see the cavitation plate on the top of the water (I have a long shaft engine on a 21" transom in case you are wondering about that). THe cav. plate is about 1" below the boat hull. The engine cant be lowered any more. We started with the engine in the next to lowest bolt holes and moved it down to the lowest hole after one trip. I am at a loss for what to do.<br /><br />longshot

 

[Dhadley]

Re: engine set up question

What brand prop? Is it brand new or new to you?But a 15 seems a little small on a light boat anyway. We may have to get you something better anyway.<br /><br />Let me know!