Evinrude 115 (Tough running under load)

JoeWall

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Jul 21, 2016
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16
So the full run down is I bought a boat with a 1977 Evinrude 115 on it about a year ago. After two weeks on the water the bottom bearings came loose and blew a hole out the side of the crankcase/block. With Evinrude the 85 and 115 are the same motor except for a few carb tweeks and the heads are a bit different sizes. So we bought an 85 block and rebuilt the motor. Cleaned the carbs and put it back together. Where I am currently is that the boat will run when good at higher RPM's. But when it drops to lower RPMs to say put it into gear/idle. It wants to give out. So far I have cleaned the carbs thoroughly. I also adjusted the idle so it has plenty of gas at lower RPM's. Ive done a link and sync to ensure the timing advances properly. We also thinned out the oil in the gas becayse we noticed it smoked a lot which indicated too much gas.

In the water the boat will run decent at lower RPM's but only if the motor is trimmed almost out of the water. Which to me indicates it doesnt do well with a heavy load on the prop. Once the boat planes out and is running it does great and will reach around 33 mph. Is there anything else I could possibly be missing from a mechanical end? Fuel pump seems to be clean as well. Any guesses are more than welcome.
 

JoeWall

Cadet
Joined
Jul 21, 2016
Messages
16
Ill add pictures of the throttle linkages and set up of the motor soon to see if anyone can spot any major issues.
 

racerone

Supreme Mariner
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Dec 28, 2013
Messages
36,031
First of all are you sure that a 1977 model 85 hp and a 1977 model 115 engine are the exact same displacement ?----The correct mixture is 50:1 on those motors.
 

CaptnKingfisher

Petty Officer 1st Class
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May 14, 2017
Messages
259
Whats your rpm at low idle? Did you set your timing on a hose? My first thought would be to advance the timing
 

Faztbullet

Supreme Mariner
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Mar 2, 2008
Messages
15,589
The 85 is a smaller displacement block you will need to rejet or recarb
 

JoeWall

Cadet
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Jul 21, 2016
Messages
16
I say this with caution but I currently do not have a working tach. I know it's hard to work without one but working on a budget and the wiring portion of boats is not my specialty. And with rejetting or recarbing, you are saying I will need bigger or smaller jets/carbs?
 

CaptnKingfisher

Petty Officer 1st Class
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May 14, 2017
Messages
259
Tinytach is a handy tool to have. Red wire wraps around your spark plug wire. Black wire goes ground, it will read your RPM
 

JoeWall

Cadet
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Jul 21, 2016
Messages
16
My other question is, we have the old 115 heads, if i put those on the 85 block would that set the displacement correctly so I could keep my carbs??
 

racerone

Supreme Mariner
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Dec 28, 2013
Messages
36,031
??-----These engines are a different displacement and a different head gasket.---------Sorry, I believe you are grasping at straws here !!
 
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