Poor performance on low rpms with Yamaha 90AETOL

[rodriesp]

Hello, I'm writing from Argentina, to see if you could give me some help with my boat that has too little thrust when getting the boat onto plane. My boat has 4,9m length (like 16 feet), and I have a Yamaha 90AETOL on it, the boat maximum supported power is 90HP, as my Yahama has.
The problem is specially annoying when skiing, as it takes lots of time to get the skier out of the water.
I'm running the engine with its original 13x19K painted steel prop. At WOT with 2 people, the engine gets about 5100rpm correctly trimmed, but it takes some time to reach these rpm. With a skier on water it will only get about 4800rpm at WOT.
I'm thinking about an engine height problem. I mounted it in the third hole, and at WOT the cavitation plate is a bit submerged (I posted some photos). So, I would like to know if you consider a good idea to try lifting the engine to the 4rd hole before testing different propellers as a 13x17.
Here you can see a short video of the engine running at WOT: http://youtu.be/HwRLv2bsOtg

 

[99yam40]

Re: Poor performance on low rpms with Yamaha 90AETOL

http://www.yamahaoutboards.com/owner-resources/performance-bulletins

Check out what a set up like yours did in these and what prop they used.
Could be just the wrong prop or motor problems.

Pulling a skier may need a different prop also

 

[SparkieBoat]

Re: Poor performance on low rpms with Yamaha 90AETOL

my guess would be you should be able to raise it to the 3rd hole. 5100 RPM is way under where you should be, check the recommended RPM range for your motor and prop it for the TOP of that range, for instance if it is 5400-5800 prop for 5800, which is more where you should be probably. if you can find a prop shop that will let you test run a few props until you find the right one, I would try a 15 pitch first and your RPMs will probably go to around 6K unloaded, but that will be great for pulling a skier up, I would also recommend a set of smart tab trim tabs, but the 15 pitch prop will make a big difference. sometimes recommended HP ratings tend to be a little on the low side, you should stay within the recommended range but I have seen a lot of 115s and even 150s on 16-17' boats, a 90 would probably be enough though with the right prop. you may even want to buy a 15 and a 17..one for skiing the other for cruising.

 

[rodriesp]

Re: Poor performance on low rpms with Yamaha 90AETOL

my guess would be you should be able to raise it to the 3rd hole. 5100 RPM is way under where you should be, check the recommended RPM range for your motor and prop it for the TOP of that range, for instance if it is 5400-5800 prop for 5800, which is more where you should be probably. if you can find a prop shop that will let you test run a few props until you find the right one, I would try a 15 pitch first and your RPMs will probably go to around 6K unloaded, but that will be great for pulling a skier up, I would also recommend a set of smart tab trim tabs, but the 15 pitch prop will make a big difference. sometimes recommended HP ratings tend to be a little on the low side, you should stay within the recommended range but I have seen a lot of 115s and even 150s on 16-17' boats, a 90 would probably be enough though with the right prop. you may even want to buy a 15 and a 17..one for skiing the other for cruising.

Well, now I'm running in the 3rd hole, did you mean I let it like that or that I raise it to the 4th hole?
BTW, the RPM range is 4500-5500, so unloaded I'm running fine, but I like your idea of getting the 5500rpm unloaded.

 

[robert graham]

Re: Poor performance on low rpms with Yamaha 90AETOL

A 90HP on a 16' boat, you should have plenty of power...are you sure the motor is tuned and running correctly on all 3 cylinders. Maybe check the spark plugs for a reading on the motor's condition?

 

[rodriesp]

Re: Poor performance on low rpms with Yamaha 90AETOL

A 90HP on a 16' boat, you should have plenty of power...are you sure the motor is tuned and running
correctly on all 3 cylinders. Maybe check the spark plugs for a reading on the motor's condition?

Well, that's sure, engine has all 3 carbs clean, as I had a problem with water on gasoline, but the solution was using another gasoline tank, now the engine runs smooth, idles perfect, on 3cyl, spark plugs are a bit oily, but not a lot, tried with new ones and it's the same. I guess it's not a problem of tuning, I mean, the engine response is strong, but very poor let's say, I don't know if you understand what I'm saying. Just to see what I tell you here is a link of me skiing, where you can check that the engine deals a lot when starting... http://www.youtube.com/watch?v=2It7w_7_Xrc
Take in mind that this happens at full throttle...
And forgot to say, engine has only 47hs.

 

[robert graham]

Re: Poor performance on low rpms with Yamaha 90AETOL

How much does your boat weigh?...maybe water in the bottom of hull/foam causing boat to be water-logged/heavy? Is there a drain plug for your bilge area? From your video it definitely looks like it's just not running strong. I run a C90HP Yamaha on my 18' boat and it has an abundance of power! Your throttles move the carb linkages And the timing linkages, and if the timing was off it would cause the motor to run weak like that. Check those linkages....you may need a manual for your motor to explain how it's set up...it has to be right. Good Luck!

 

[SparkieBoat]

Re: Poor performance on low rpms with Yamaha 90AETOL

I meant that you should be able to go to the 4th hole...general rule of thumb is ..get it as high as you can with out it cavitating in the turns. make sure to check your water stream at all RPM ranges, so you know it is not having trouble picking up water. less motor in the water = less drag = more speed = better MPG and overall performance. I have a 115 on my 19' boat and I have no where near an abundance of power..going to a 150..but one mans "abundance of power" is another mans "this is way too slow." a lot depends on the hull design and weight of the boat. I would absolutely prop for 5500 RPMs with 2 people.

 

[yamatech43]

Re: Poor performance on low rpms with Yamaha 90AETOL

I agree with Robert to check the boat's weight....could be waterlogged....from picks the motor looks to be correctly mounted....doesn't look too low to me....and the way you describe the slow rise to rpm is classic for a heavy heavy boat OR one that has a prop that is too much...if you don't have a scale to weigh boat then easiest thing would be to borrow a 13x17 prop from prop shop(they should have loaners for this) but I sure would weigh the boat if I could....good luck.

 

[SparkieBoat]

Re: Poor performance on low rpms with Yamaha 90AETOL

in the pic it looks like you have the motor trimmed up a decent amount, the higher you get it the less you will need/be able to trim, but the better it will perform, so long as water is being picked up and you are not blowing out in the turns. I looked at a few of your youtube post..that is a nice boat..probably a 17 1/2 foot Key west 176 sportsman. I see a lot of those with 115s around here. looks well kept..I doubt you have water log issues..but it would not hurt to check. I did a quick search of those boats for sale and found a good number of them with 115s one even had 140 on it.

 

[99yam40]

Re: Poor performance on low rpms with Yamaha 90AETOL

Yamaha makes test props for motors, see if you can get someone with one for your motor to test yours.

Just mount it and back into the water, no need to even get it off of the trailer. Warn it up and then open the throttle.
If it cannot get up to the proper RPM, then you have motor problems, if it does then the motor is OK.

Has this boat and motor ever run properly or has it always been slow to plane?

If you ran this for long with water in the fuel you could have hurt the motor some from lean burning cylinder or 2 and need to do the basics like compression to make sure cylinders are sealing properly.

You could still have water in the carbs from some trapped in lines and pump even though you switched tanks and cleaned carbs.

Did you check out the link I posted to see what a setup like yours should run and what prop they used?

really sounds like over propped even if the motor is healthy

 

[rodriesp]

Re: Poor performance on low rpms with Yamaha 90AETOL

Hi guys,
First of all, I would like to thank you for all your replies, I'll take all your points into account when I take the boat out of the water, surely in some months as I wouldn't have the necessary time now. I'll probably start fixing the internal gasoline tank, so I can check if it is waterlogged, and then I'll check the other things as engine height and different propellers. I'll be doing this in some months as I won't have the necessary time now.
For the people who asked about the boat, is a boat made here in Argentina, we have a lot of makers with excellent quality, my boat is an Fishing 490 from Astillero Arco Iris, here is the link where you can see some photos http://www.astilleroarcoiris.com/fishing490sporte11.html

 

[robert graham]

Re: Poor performance on low rpms with Yamaha 90AETOL

It's a good looking boat, well made and maybe it's just a bit heavy for your 90HP motor....maybe boat is underpowered?

 

[rodriesp]

Re: Poor performance on low rpms with Yamaha 90AETOL

It can't be underpowered as the maker says that the horsepower rate is 50-90HP...And I also now guys that use them with 60HP, but skiing, but they run perfect...and before this engine I had an Evinrude 70HP which went the same or better...

 

[99yam40]

Re: Poor performance on low rpms with Yamaha 90AETOL

If the 70 ran the same, does that mean it was slow on planeing also?
What happened to that motor? did it blow?

Like I said before a test prop will show if you have a motor problem,
then you can chase what ever the other problem is.
Over propped or water logged hull

 

[SparkieBoat]

Re: Poor performance on low rpms with Yamaha 90AETOL

I looked at the wrong you tube video..I thought it was yours. That is a nice looking boat, but it looks like a boat I would expect to see a 90-115 HP on. not a 50 - 70. but if a 70 went as good as your 90 is doing you defiantly have a problem somewhere. you should do a spark test and compression check..a 17p prop will help some, but if what you say is true you are missing some HP.

 

[metor99]

Re: Poor performance on low rpms with Yamaha 90AETOL

I agree with SparkieBoat you will need a 17 pitch prop with this boat and especelly when pulling someone. also your motor is too low on the transom. lifting and trim will get your rpm's up. Sounds like it has a 19 pitch prop on it now.