Motor height help ? Sun Tracker 21 50HP

[j33p]

Hello everyone, pretty new to owning a pontoon boat. I picked this 2008 Sun Tracker 21 with a 50HP Merc on the back and for the life of me cannot get this thing to cruise at a decent speed. Done a ton of googling and it's like the motor "spins out" and it looses all traction, I have to back off the throttle, then I can go again for a bit. I think this is cavitation?

I have always been thinking the motor is low enough, but it's mounted as low as I can go and changing the trim doesn't seem to do much. Any toon experts able to look at the attached pics and comment if it looks like the motor is mounted too low? From what I found the plate should be in line with the bottom of the transom, which isn't the case here. Anyways, I thought I would ask the community. Thank you for your help in advance.

It's also running a stock prop

Like I said, I am a total newbie when it comes to a pontoon boat, so please bear with me a bit.

 

[ahicks]

That issue you're thinking might be cavitation could easily be a prop hub that's slipping. There's a rubber hub that insulates the prop from the drive shaft. If it goes bad they'll do exactly what you're describing.

 

[HotTommy]

Judging from the water line on your boat, your motor is not too high. I agree with ahicks analysis.

 

[j33p]

Ok thanks, I'll pull the prop off, hopefully it's as easy as my 9.9 Johnson Thanks for the tip.

 

[HotTommy]

If you have a chance to run the engine before you pull the prop, you can confirm the diagnosis by putting a mark on the hub and prop. After you briefly sense the "cavitation" sound, check and see if the marks are still aligned. If they are no longer aligned, you have confirmed that the hub is slipping inside the prop.

 

[ahicks]

You can check for sure pretty easily if it's in the water. Mark the prop and the hub, go run it until it slips, then come back and check your marks. If it's the hub thing like we're thinking, the 2 marks will no longer be in alignment.

 

[j33p]

Good tips, thank you

 

[randy ussery]

check the cupping on your prop as well, over time with continued usage, the cupping will wear away and the prop will start to slip in the water, most noticeably when turning at higher RPM.. the cavitation plate on your motor appears to be a few inches low, it should be in a parallel line with the bottom of your motor pod, If its to deep it will create a leak path for air to reach the prop and induce slippage via cavitation.

 

[j33p]

check the cupping on your prop as well, over time with continued usage, the cupping will wear away and the prop will start to slip in the water, most noticeably when turning at higher RPM.. the cavitation plate on your motor appears to be a few inches low, it should be in a parallel line with the bottom of your motor pod, If its to deep it will create a leak path for air to reach the prop and induce slippage via cavitation.

Thanks Randy, I don't see any previous marks in the paint that would indicate the motor was every mounted higher. I marina I bought it from says the previous owner claims this problem wasn't there. The bearing carrier had a chunk missing out of it, so they have replaced that at least. I am wondering if a log/rock was clipped and it chipped the carrier and maybe spun the hub.

Hoping to be able to check it out some more this weekend.

 

[Silver Eagle]

I'd put the motor in gear, not running, and see if you can turn the prop.

 

[j33p]

So I pulled the prop and pulled the hub out which is one of these
http://bblades.com/shop/hub-kits/mercury-hub-kits/flo-torq-reflex-hub-kit-mercury-835257q12/

Visually , everything looks fine.

Got the toon in the water with 4 of us on it, all located at the back, hit the gas, and you could tell it was working, then it "slipped", did it a few times. The notice the trim wasn't ALL the way down, so did that, and was able to cruise around as long as everyone was at the back. I guess this would indicated a problem with the motor position ? It's at it's lowest setting and looks like it's always been in that position.

I'll try to find another tracker 21 in my area and go take a look to see the motor position

 

[mayorjones]

I hate to be the bearer of bad news, but....

I purchased that same exact set up and tried everything - different props, engine height, etc... and came to believe that it simply is the wrong motor for that boat and traded the 50 for a new 60hp MetcuryBigfoot and have had zero problems since. I run mine on the Mississippi and especially in current it was HORRIBLE. I even got Tracker Corporate involved, but they weren't much help. Love the boat but that 50 hp standard motor just wouldn't work for me.