Mercury 115hp wot questions and parts

Jhwaco

Cadet
Joined
Jul 13, 2019
Messages
18
I have a 96 115hp off shore engine that’s needing some parts and tune up I’m guessing. Not sure the best place to buy what I’m needing. Going across the lake WOT the engine seems to lean out. No difference between 75-100% on throttle engine backs off few hundred rpms you can hear it change sound but it’s not instant it’s over a few mins. If you bring back to 50 percent for little while then back to wot it picks back up great again. I looked at the primer bulb and it’s not sucked down. So I was going do a tune up. Plugs plug wires, fuel pump rebuild, speedo tube and then there two rubber mounts at the bottoms of the engine that’s gone I’ll need to replace. I’ll post pic of that. Thanks for any advise in advance.. I did a compression test on it last night all in the 120s. The plugs didn’t look like they been running lean either in my opinion
 

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Texasmark

Supreme Mariner
Joined
Dec 20, 2005
Messages
14,544
Not sucked down only means restriction/malfunction on the distribution side of the bulb, not the inlet side. You need to be looking at the fuel pump and engine fuel charging circuits for proper functioning. You are looking for fuel charging circuits letting you down so you squeeze the bulb and check for rpm improvements...if so go after clogged engine fuel filter, carb cleaning, fuel pump OH kit....., deteriorated engine fuel hoses releasing little black rubber particles in the fuel line which clog filters and carb jets.

Carbs may be in need of rebuilding...if cruded up, needle valve/float not functioning correctly in the carbs...may be just one or all.
 

Jhwaco

Cadet
Joined
Jul 13, 2019
Messages
18
I’ll go back out this evening and try the primer bulb to see if it picks up rpm. I had it tuned up a couple years back. They replaced all fuel lines and rebuilt carbs but they did tell me with today’s fuel they have seen carbs mess up within just a few weeks with the fuel quality. Thanks for the info. I’ll get back with the results
 

jimmbo

Supreme Mariner
Joined
May 24, 2004
Messages
12,944
If the engine is leaning out at full throttle, but isn't at 80%, it is pointing to a restriction in the fuel supply, the last few hundred RPMs burn a lot More gas.
 
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