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Why does this Evinrude Etec throttle down at WOT?

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Friend has a 2014 Evinrude Etec 115 horse on his boat. At wot it goes about 38 mph according to the speedometer and fish locaters GPS. At wot of 38 mph after a few mins it usually throttles down on it’s own to about 36mph for no reason. If you throttle back and then throttle up to wot again it goes back up to 38mph. If you don’t it will just keep going at the slower speed. 

 

Whats going on here?

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Assuming his motor has the correct prop and isn't on a 21ft glass boat, he's about 8-12mph off top end speed. He should be getting 45-50mph /w the 115. Sounds like the motor is down a cylinder.  Could be an air leak in the hose, fuel pump sticking, carbs gummed up, bad gas, etc. Need more info unless you want to throw darts at it. What RPMS is the boat at when WOT, are the fluctuating, etc. 

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32 minutes ago, iabass8 said:

Assuming his motor has the correct prop and isn't on a 21ft glass boat, he's about 8-12mph off top end speed. He should be getting 45-50mph /w the 115. Sounds like the motor is down a cylinder.  Could be an air leak in the hose, fuel pump sticking, carbs gummed up, bad gas, etc. Need more info unless you want to throw darts at it. What RPMS is the boat at when WOT, are the fluctuating, etc. 

 

RPMs are about 5,500-5,600. It's a 19 foot glass bass boat.

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115 ETecs are supposed to be propped for 5500-6000 so he's on the bottom end. You'll lose 1-200 RPMS and 1-2 MPH in the summer /w water temps being high as well. And when you say "throttle down" that would indicate that it's droppng in RPMS so how many RPMS is it dropping? Could be boat isn't propped correctly, engine height could also be wrong. Regardless, 36-38 is way too slow for that set up unless his boat is waterlogged. Ignore the onboard speedometer. It's useless and not accurate. Make sure the GPS on his boat unit is set for MPH and knot KTS. 36-38 KTS is 47 +/- in MPH. There's a ton of reasons for why a boat drops in speed on an Etec. Check gas line, gas, pump, filter. Start there /w the easy stuff. 

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6 minutes ago, iabass8 said:

115 ETecs are supposed to be propped for 5500-6000 so he's on the bottom end. You'll lose 1-200 RPMS and 1-2 MPH in the summer /w water temps being high as well. And when you say "throttle down" that would indicate that it's droppng in RPMS so how many RPMS is it dropping? Could be boat isn't propped correctly, engine height could also be wrong. Regardless, 36-38 is way too slow for that set up unless his boat is waterlogged. Ignore the onboard speedometer. It's useless and not accurate. Make sure the GPS on his boat unit is set for MPH and knot KTS. 36-38 KTS is 47 +/- in MPH. There's a ton of reasons for why a boat drops in speed on an Etec. Check gas line, gas, pump, filter. Start there /w the easy stuff. 

 

He just tried two different props. A 13x21 and 13x19 I think. 13x21 was about 6,200rpm and the 13x19 is the 5,500-5,600rpm.

 

He had the motor serviced and diagnostic'd last year because he thought it was smoking too much and it was passed inspection fine.

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What's the engnie height and prop to pad then? Prop is only part of the equation. Granted a 115 on a 19ft boat is underpowering the hull but you're still about 10MPH slow on what the top end should be. Start trouble shooting. 

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9 minutes ago, iabass8 said:

What's the engnie height and prop to pad then? Prop is only part of the equation. Granted a 115 on a 19ft boat is underpowering the hull but you're still about 10MPH slow on what the top end should be. Start trouble shooting. 

 

I don't know what prop height to pad means.

 

 

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Google "prop to pad height"

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2 hours ago, iabass8 said:

What's the engnie height and prop to pad then? Prop is only part of the equation. Granted a 115 on a 19ft boat is underpowering the hull but you're still about 10MPH slow on what the top end should be. Start trouble shooting. 

 

 

I guess it’s 8-1/2” inches. 

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So you're saying that you are getting the following from:

 

Ground to pad of boat minus Ground to center of prop shaft=8 1/2 inches? You want that number to be 3.5 inches......

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12 minutes ago, iabass8 said:

So you're saying that you are getting the following from:

 

Ground to pad of boat minus Ground to center of prop shaft=8 1/2 inches? You want that number to be 3.5 inches......

 

Ground to Pad was 17”. Prop shaft to ground was 9-1/2” inches he said. Subtract 9-1/2” from 17” is 8-1/2”.....I think. lol. 

 

It’s mounted right to the boat. No jackplate. 

 

 

 

 

 

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4 minutes ago, tcbass said:

 

Ground to Pad was 17”. Prop shaft to ground was 9-1/2” inches he said. Subtract 9-1/2” from 17” is 8-1/2”.....I think. lol. 

 

It’s mounted right to the boat. No jackplate. 

 

 

 

 

 

You want the prop shaft 3.5in below the pad of the boat. Sounds the engine is mounted way too low if you're doing this correctly. 

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1 hour ago, iabass8 said:

You want the prop shaft 3.5in below the pad of the boat. Sounds the engine is mounted way too low if you're doing this correctly. 

 

 

True. After looking at it I don’t think there is any other way to mount it without using a jackplate to raise it....

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Why not just raise the motor up a hole or two and go from there...that engine should have 3 bolt holes on each side that the motor is bolted into

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23 minutes ago, iabass8 said:

Why not just raise the motor up a hole or two and go from there...that engine should have 3 bolt holes on each side that the motor is bolted into

 

O. I’ll ask him. Wouldn’t a shop have to do that?

 

 

And this problem could cause the engine to throttle down?

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You still haven't said if the engine was losing RPMS when it was throttling down. 

 

No a shop doesn't need to drop and engine down if you know how to. If you don't, then yes they do.

 

Will it solve this issue? Possibly. Judging by how your friends boat is set up he might have a whole lot more going on. If his set up has been that off for however long he's owned it, it could do a lot of internal harm to a motor. 

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Just now, iabass8 said:

You still haven't said if the engine was losing RPMS when it was throttling down. 

 

No a shop doesn't need to drop and engine down if you know how to. If you don't, then yes they do.

 

Will it solve this issue? Possibly. Judging by how your friends boat is set up he might have a whole lot more going on. If his set up has been that off for however long he's owned it, it could do a lot of internal harm to a motor. 

 

 

Im pretty sure he said rpms did not go down, which would be weird right? 

 

I dont understand how the motor being mounted too high can cause the motor to decelerate though?

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The engine, according to what you've provided, is mounted too LOW, not high. For starters, a 19ft boat isn't going to perform as well as it should /w an undersized motor. Your speed of 36-38MPH is 10+ MPH TOO SLOW for what it should be moving at. I would be more concerned about that at the moment than a 2mph fluctuation. If he's seeing not seeing an RPM drop, it could be his electronics aren't correct. I would be way more concerned about the engine losing 10+ MPH top end from what it should be at. If your numbers are correct, his motor is 5 inches too low and is putting a lot of strain on the motor. 

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16 minutes ago, iabass8 said:

The engine, according to what you've provided, is mounted too LOW, not high. For starters, a 19ft boat isn't going to perform as well as it should /w an undersized motor. Your speed of 36-38MPH is 10+ MPH TOO SLOW for what it should be moving at. I would be more concerned about that at the moment than a 2mph fluctuation. If he's seeing not seeing an RPM drop, it could be his electronics aren't correct. I would be way more concerned about the engine losing 10+ MPH top end from what it should be at. If your numbers are correct, his motor is 5 inches too low and is putting a lot of strain on the motor. 

 

Would that cause to smoke?

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Just now, tcbass said:

 

Would that cause to smoke?

Smoke is generally a sign of over heating or something burning/melting under the cowling. If you got it checked out last year and it was ok, it was probably just water vapor. The print out the tech ran, or should have ran, will give you the temps of each bank. Assuming he looked at them and they were in spec, it was probably fine. Etecs will "smoke" when the water temp is warmer than the air temp. It's just water vapor that disappears as fast as it comes out. Totally normal. I have a '17 etec that will do it in the AM when it's 60 degrees and the water is 75. Goes away as the day goes on. 

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Update:

 

Friend took boat out for a fishing trip and went to all of the same locations that he always goes too. Of course the problem did not replicate itself this time.

 

Hmmmm........

 

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Sounds like a 25" long shaft in lieu of a 20"  if the centerline of the prop shaft is 8 1/2" below center of the plane pad surface. Should be 3 1/2" as stated earlier.

3 blade 20 pitch prop would be average for this boat, with 115 hp a 19' unknown brand bass boat is under powered, should look at the max hp rating for this boat.

Not familiar with this engine, however dropping rpm's could be the computer kicking in to save the engine from overheating?

Tom

 

 

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56 minutes ago, WRB said:

Sounds like a 25" long shaft in lieu of a 20"  if the centerline of the prop shaft is 8 1/2" below center of the plane pad surface. Should be 3 1/2" as stated earlier.

3 blade 20 pitch prop would be average for this boat, with 115 hp a 19' unknown brand bass boat is under powered, should look at the max hp rating for this boat.

Not familiar with this engine, however dropping rpm's could be the computer kicking in to save the engine from overheating?

Tom

 

 

 

 

Interesting point. 

 

 

He said he helped tow a guy who’s boat had died. When he did lots of smoke. Whitish color but when he stopped towing him back to no smoke. 

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