need prop help

[PEA]

I bought a used motor (1996 85 hp yamaha) for my 24' pontoon boat. It came with a 15 pitch 13.25 dia. SS Stiletto propeller. I ran the boat at the local lake and could only get about 3200 rpm out of it. Motor seemed like it had more to give but was lugging around. Any suggestions would be greatly appreciated.

 

[Snake334]

Re: need prop help

This sounds kinds like what I'm about to deal with. I just bought a 1998 70hp Johnson for my 24' pontoon. I got it from a marina that had taken it off of one of their rental pontoons when they upgraded. It has a 13.5X15 prop on it. They said thats what they ran on it with their pontoons, but I'm skeptical. I'm in east Tennessee, so it's gonna be a couple months at least before I can even get out on the lake to try it out. I hope who ever can answer your question, can help me out as well.

 

[Richeld]

Re: need prop help

Check your coils to each spark plug.
I had one spark plug coil wire come loose and it made a big differance in sluggish to full use.
richeld

 

[crb478]

Re: need prop help

3200 rpm seems low for a 85 hp motor on an average 24 ft pontoom with a 15 pitch prop. I would expect it to be somewhere in the 4000 rpm range on average, but each boat is different. How much does your pontoon weigh? Are the pontoons free of water? Is the motor rinning right so you actually get 85hp? You may well need to drop down to a 13 or even and 11 pitch prop, but it looks to me that the problem may be elsewhere, either excessive weight or under preforming motor. You might get a 400 rpm jump in rpm for each pitch drop but at that rate you would need an 9 pitch which seems to be too little

 

[lncoop]

Re: need prop help

3200 rpm seems low for a 85 hp motor on an average 24 ft pontoom with a 15 pitch prop. I would expect it to be somewhere in the 4000 rpm range on average, but each boat is different. How much does your pontoon weigh? Are the pontoons free of water? Is the motor rinning right so you actually get 85hp? You may well need to drop down to a 13 or even and 11 pitch prop, but it looks to me that the problem may be elsewhere, either excessive weight or under preforming motor. You might get a 400 rpm jump in rpm for each pitch drop but at that rate you would need an 9 pitch which seems to be too little

+1. I suspect there's something else going on. 13.25 x 15 should be fine for that motor, but even if it isn't ideal, you're not going to be able to prop down enough to get into your recommended RPM range. Prop experimentation can get expensive and frustrating in a hurry, so do yourself a favor and exhaust all other possibilities before you mount that horse. I bet you'll find the problem is something else entirely. Good luck.

 

[PEA]

Re: need prop help

Thanks for the feedback. Just had a tune up and carb job. Runs very nice and smooth staticly. Toons are dry, boat has most of the furniture out at this time. Not sure of the weight. idles from launch to main lake effortlessly. She pegs out at 14.5 mph (wot) you can feel it trying to give more thrust but just cant so she lugs.

 

[Jeep Man]

Re: need prop help

You might want to have your prop checked. I had a 14x11 on my 60hp Bigfoot and was told it was the proper pitch, but could not get the rpms. Switched to a 14x9 and then was over-reving. I had the old one rebuilt and now I'm at 5800 WOT, which is where I'm suppose to be with this motor.

 

[lmuss53]

Re: need prop help

What diameter are your logs? 3200 seems really low for the 85 on a 24 foot boat. Check the prop and see the numbers for yourself, maybe you got a 21p off of someones runabout instead of what you thought you got.

 

[PEA]

Re: need prop help

Great Forum ! Thanks for all the input. I will be trying a 14 X 11 pitch prop today, weather permitting. I will post the results ASAP.

 

[lncoop]

Re: need prop help

Great Forum ! Thanks for all the input. I will be trying a 14 X 11 pitch prop today, weather permitting. I will post the results ASAP.

Please do, 'cause I be stumped. Good luck my friend.