What rpm should I be at

[awe1979]

I have a 17 ft fish and ski with a 1995 johnson 90 hp cross flow. I run a 15 pitch prop and do 5400 rpms loaded the way I normally use the boat is that too little rpms? Should I be closer to 6000?

 

[tashasdaddy]

Re: What rpm should I be at

5400-5600 is good.

 

[awe1979]

Re: What rpm should I be at

Thank you I was worryed that I was too low. This will put my mind to ease.

 

[Dhadley]

Re: What rpm should I be at

5400 is border line lugging. The motor would be much "happier" at 5800 and live longer. If you keep the top rpm at 5400 max, just be sure to decarbon as recommended (every 50 running hours) or perhaps every 35 hours.

 

[awe1979]

Re: What rpm should I be at

So which is it am I fine or do I need to go with a 13 pitch prop.

 

[Dhadley]

Re: What rpm should I be at

Dropping pitch to gain rpm is only an absolute last resort. Most times that results in a decrease in efficiency. If it were me I'd work with the set up and the current prop to reduce drag. That will increase efficiency across the board from holeshot to wide open.

 

[awe1979]

Re: What rpm should I be at

What do you mean is there something I can do to this prop?

 

[Dhadley]

Re: What rpm should I be at

I'd look at set up first. If the motor is mounted all the way down on the transom, move it up a hole or two. We'll assume, for the moment, that it's bolted to the transom and not on a jackplate.

Moving the motor up will reduce gearcase drag and improve everything from holeshot to top rpm & speed. Generally speaking, as long as your existing prop is in good shape, if you can use all or nearly all of your trim range without the prop venting, the motor is mounted too low for that prop.

 

[awe1979]

Re: What rpm should I be at

Yes I can only trim about 1/2 way up on the guage. Or the prop slips like crazy. So I should try moving the motor up one bolt hole.

 

[awe1979]

Re: What rpm should I be at

And no its not on a jack plate. I dident think you could adjust them without a jack plate.