77 Evinrude 115 hp won't go faster than 20 mph

interalian

Commander
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Jul 23, 2009
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Also you want the ability plate in the water right?

Lots of really fast boats run full tilt with the propeller hitting air. If you have too much of the leg in the water, you get drag.

But based on your blowout issue, I really can't understand why having the leg deeper would do that. Bear in mind that when you're 'on plane', the water just aft of the transom will rise upward as the boat passes. This is why it's preferred to have the AV plate level with, or just above the keel line.
 

Ktgritz

Seaman Apprentice
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Jul 22, 2017
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I've been all over the boat and it is fairly dry. I had the floor up and everything was good.
 

Ktgritz

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Do you think it would be worth seeing if I can film it with a go pro or something?
 

interalian

Commander
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Jul 23, 2009
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If you can mount it so it records what's happening at the waterline in front of the leg - shoot from the top corner of the transom. That would be very telling.
 

jbuote

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Aug 17, 2016
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1,001
And in case you hadn't thought of it already, make sure to put some kind of safety line on the go pro..
​I've seen a couple vids where the go-pro fell off, and they had to go diving to get it back.. lol..
 

Faztbullet

Supreme Mariner
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Mar 2, 2008
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15,589
If any of that plate is hanging below pad it can turn the water from lower unit....
 

Ktgritz

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Jul 22, 2017
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This is dead Center of the boat
 

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interalian

Commander
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Jul 23, 2009
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From that shot, you have about a foot of width of the original hull that's lower than the diamond plate. Maybe a video would be the best next step here.
 

oldboat1

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Apr 3, 2002
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Looked at the uTube clip a number of times, and think I see a little bit of movement at about the time she is losing bite -- though maybe imagining it after viewing too often.

Is that motor flexing on the transom? I don't see a thrust rod in place, so assume the motor isn't locked down. Also don't know how solid the transom is.

Additionally, I'm hearing a little bit of roughness (chugging) at start up, although It seems to even out some -- not sure if that's symptomatic.
 

Ktgritz

Seaman Apprentice
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Jul 22, 2017
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Transom is solid the movement your seeing is the ever so slight play in the tilt cylinders and yes it has a low speed high load miss fire wasn't noticeable till I put the 21 pitch prop on it. I'm assuming because it was able to rev faster with the 17 pitch. It has to be ventilating from somewhere but I'm still at a loss. Tonight I will be taking my buddy out to video it from the back.
 

oldboat1

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Has it run that well for you? If so, should revisit changes made since then. If hasn't run that well, I would look at engine operation first (ignition/tune up/troubleshooting. compression test.)

[ed. fuel? fresh 50:1. Water in existing tank?)
 
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Ktgritz

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Jul 22, 2017
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If you watch the first video with headphones you can hear me reving it up but not going any where the power head runs good. The only thing that has changed is the prop and I had the clutch dog and gears machined. It has never gone that good for me.
 

oldboat1

Fleet Admiral
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Apr 3, 2002
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Check compression and post numbers -- start from there. If compression numbers are acceptable, go back to the aluminum prop and boat test again.
 

oldboat1

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good thinking. Can now see if there are any changes from baseline.
 

Ktgritz

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Jul 22, 2017
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Like check compression again? I just bought it on the 3rd of July only had it out 4 times maybe 2 hours total run time on the outboard the rest was trolling motor.
 
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