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1977 Johnson 85hp looking for better top speed.

I have a 1977 or so Johnson 85hp V4 on my 1980's 16ft fibreglass Thundercraft, after blowing a bottom end on my 1977 Johnson 70hp recently I switched to this motor because I had it already, the old 70Hp I was able to get with just me in the boat and the gear 55kmh top speed with a 14x17 Prop. Now when I switched to the 85 I figured 15 more hp= worse mpg better holeshot and better top speed... Well not exactly... Holeshot and corner power are a little better, mpg is a little worse but top speed is alot worse... With just me and the gear it gets 47-50kmh max...

Currently it's running I believe a 13-3/4x15 prop, (can't check rpm don't have a tach on the boat) but it sounds about 5,500 it sounds about the same as the old 70, I was told by several people at the local boat shop that the reason I'm slower is the style of prop (forget exactly what they called it but it's straight cut at the ends) and size/pitch, they said to try a 14x17, so I put the 70hp prop on expecting to atleast be back to what I had with the 70... Nope, pretty sure the holeshot was worse then the old 70 and slower top speed, best I could get was 44-45kmh... And I lost alot of RPM, How do I atleast get my top end back? Preferably if I'm burning more fuel and have 15 more horses actually gain top speed... I would love to get around 60kmh if possible.

Picture of the boat is with the old 70hpScreenshot_20220817-183636_Gallery.jpg
 
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Some will argue.-----I would say there is something wrong with the 85 HP.-----Start with a compression test.----Post the numbers.-----Or run it on a marine dynamometer to see if it putting out proper power !!
 
Some will argue.-----I would say there is something wrong with the 85 HP.-----Start with a compression test.----Post the numbers.-----Or run it on a marine dynamometer to see if it putting out proper power !!

Ok so I'm not sure what these motors should be running but I believe I remember reading somewhere about 120 PSI. Starting at the top right the right side is about 115-117 and the left side is about 119. Tested every hole twice. When I took the plugs out the right side was black but I have seen worse, the top left looked pretty good, the bottom left I don't know what to make of it, you can't really tell by the pic but it almost very clean, and shiny, like it hadn't even been installed and ran before. The plugs sitting higher in my hand are the top plugs. From my research though the carbs have fixed jet sizes and don't have any adjustments, is this correct?
 

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Pull the bypass covers.----Inspect pistons/ rings.----I believe you have some serious issues with this wonderful V-4 motor.
 
Pull the bypass covers.----Inspect pistons/ rings.----I believe you have some serious issues with this wonderful V-4 motor.

What exactly do you mean by bypass covers? Also what am I going to need to seal it back up after? I assume I can't just reuse the same gasket. What kind of compression numbers should I be seeing on this old girl?
 
Each cylinder has a cover on the side.----6 wee bolts.------May need a new gasket.----Pull it off first for the cylinder with 104 PSI shown in the first picture.-----There is something wrong with your motor.-----Good trouble shooting will find the answer quickly !!
 
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Each cylinder has a cover on the side.----6 wee bolts.------May need a new gasket.----Pull it off first for the cylinder with 104 PSI shown in the first picture.-----There is something wrong with your motor.-----Good trouble shooting will find the answer quickly !!

Ok well I have a birthday party that's been planned for a couple months this weekend and I promised I'd bring people tubeing and it's still running pretty good except for the odd slight cough (could be still some dirt left in the carbs) so I won't tear into untill about Monday. I'll post what I find though when I open it up. Might be time for the old girl to get freshend up at the end of this season.
 
Each cylinder has a cover on the side.----6 wee bolts.------May need a new gasket.----Pull it off first for the cylinder with 104 PSI shown in the first picture.-----There is something wrong with your motor.-----Good trouble shooting will find the answer quickly !!

Ok so I had the engine cowl off last night doing a few things and while I was under there I didn't see any covers on the cylinders? Only "covers" I saw were the heads, I even Googled a picture of the bypass covers to see what they looked like. Did the 76-77 motors have them?
 

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???----There are 2 covers on the one side and 2 covers on other side .---Held on with 6 screws each cover as per post #6.----And these crossflow V-4 blocks all these covers from 1958 to 1998.----So for 40 years or so !!!----Solenoid is mounted on one of these covers.
 
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I haven't got a chance to look yet, been terribly busy with work and personal things I haven't even had a chance to even empty the gear from that weekend... I'm also leory of taking that cover off and missing the last little of what's left in the season trying to find or wait for a new gasket. Can I use some high heat RTV/RVT? The stuff used on headers as a new gasket?
 
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