'95 Mercury 115 2+2 0G280709, recent loss in power

[Messing About]

I've owned the boat/motor for 6 months and run it several times every month.
Used to run 37-39 MPH at 5500 RPM at WOT.
Recently started have a much weaker hole shot, although can still plane out with me alone aboard. With 2 of us, no.
Top speed is now only 25 and RPM sounds/feels noticeably weaker, maybe about 3000?
Faria tach used to work intermittently but now won't register at all.

Only recent issue before this was getting stuck on the sand flats and resulting in a slow to peeing motor.
It did finally start to pee and I made it home. I did a new complete water pump kit, including gear case cover. Old one was pretty crusted with sand in the crevices. I changed gear oil and old looked dark but good. I changed both fuel filters and found a double pin hole in the inline filter tube, before the filter. Not sure if I did it during the change or it was existing, but nonetheless, I changed the tubing.

Did a sea trial and the performance is still the same poor power. Pee hole on muffs starts faster, is stronger but sputters.

I researched repair records from prior owner and found a shop repair ticket from 2 years ago that read, "slight knock in engine, intermittent alarm. Found main jets in carbs in wrong positions. Put main jets in their proper place. Replaced spark plugs and primer bulb. Knock is 98% gone." For the record, I don't notice any knock.

Any ideas as to my loss in power? Remember this is the 2+2 cylinder. I have a comp tester but haven't gone there yet.
It starts, idles and shifts just as fine as ever. Thanks in advance for the courtesy of expert replies.

 

[racerone]

Re: '95 Mercury 115 2+2 0G280709, recent loss in power

The compression test is # 1 on your list of to do.------Then check for strong spark on all 4 cylinders.--------Strong spark is spark that will jump a gap of 3/8" or more !

 

[carholme]

Re: '95 Mercury 115 2+2 0G280709, recent loss in power

Your s/n comes up as:

MERCURY - (115 H.P. (1995 ))
Serial No: 0G280709 Model No: 1115412RD

Parts list for model 1115412RD:

100/115/125 H.P. 80 JET (4 CYLINDER) - Mercury, Mercruiser, Force, etc. Parts Lookup

The service manual you require is P/N 90-830234. If you do not have this, see my message to you in Notifications at the top of this page.

To check your tachometer you can check the grey wire coming from the Voltage Regulator/Rectifier, through the terminal block and forward to the tachometer.

Gerry

 

[Messing About]

Re: '95 Mercury 115 2+2 0G280709, recent loss in power

Compression results, from the top down: 128, 126, 130, 132. Plugs are gapped at .55 for first 3, .53-54 for the last one.
Don't know how else to check for spark?
Thank you for the manual and model reference. Any ideas on what to check next for my power loss?

 

[carholme]

Re: '95 Mercury 115 2+2 0G280709, recent loss in power

Plugs should be:

NGK BP8H-N-10
0.040 in. (1.0mm) and jump a 7/16" gap

Gerry

 

[Messing About]

Re: '95 Mercury 115 2+2 0G280709, recent loss in power

Those are the model plugs I have...they are 2 years old, according to my service records.
Are you saying they should be gapped at .040?
I don't understand how I verify "jump a 7/16" gap"?

 

[carholme]

Re: '95 Mercury 115 2+2 0G280709, recent loss in power

If you look in Specifications in the manual you will see the gap and if you look in Special tools in the Ignition section, you will see a spark gap tester. You should be able to get one at almost any auto store.

Gerry

 

[racerone]

Re: '95 Mercury 115 2+2 0G280709, recent loss in power

Your motor has sparkplugs gapped at say 0.040"----Many folks think that it is good enuff to see spark jump that gap.---------Fact is the ignition system was engineered and built ( at some cost ) to be able to jump a gap of 7/16" or more.----That is a functional test of your ignition system.-----If it can not jump a gap that big there is something wrong !!!

 

[CharlieB]

Re: '95 Mercury 115 2+2 0G280709, recent loss in power

Under compression a LOT of air is squished into that gap, greatly increasing the resistance to an arc.

A hot blue arc across a 7/16 gap in free air proves the voltage necessary to fire the plug under compression at WOT.

Hopefully regapping your plugs, and/or a new set will make a big difference.

I am more concerned about jetting. I stated your returned the jets to their correct positions. Did you check the service manual and parts catalog to determine which carbs get which jets? This is important as the lower cyls I think it was #3, gets a larger jet to run a bit cooler. Run too hard with the smaller jet can raise the piston temp and cause a 'knock' as the increased heat accelerates that piston skirt wear.

 

[Messing About]

Re: '95 Mercury 115 2+2 0G280709, recent loss in power

So like I said, the old plugs were gapped too wide, at .55 and one looked a little corroded, although didn't smell burned.
I put all new plugs in, which ironically came gapped at .040 from the box. I also disconnected the tach and went for a sea trial.
Bam! Out of the hole, up on plane and old max power to 38 MPH in a moderate chop.

Went to the dock and re-connected the tach. It doesn't work but the boat still ran like her old self.
I think I read on here that Faria will service or replace their tachs for $40?

Thanks all
Bill
94 Classic Mako 161 Flats
95 Mercury 115 2+2

 

[gbrowne9]

Re: '95 Mercury 115 2+2 0G280709, recent loss in power

you are running that motor at to high max rpm.max rpm is 5250 and if you keep running it at 5500 it will fly apart.

 

[gbrowne9]

Re: '95 Mercury 115 2+2 0G280709, recent loss in power

i would test your stator high speed windings. max rpm on all the 2+2,s is 5250. if you keep running at 5500 it will fly apart.

 

[Messing About]

Re: '95 Mercury 115 2+2 0G280709, recent loss in power

Tax has worked intermittently since I owned it and now not at all...chances are the readings can't be relied on. Will have it repaired or replaced and verify max RPM. Thanks.

 

[CharlieB]

Re: '95 Mercury 115 2+2 0G280709, recent loss in power

5500 WOT RPM on a lightly loaded boat shouldn't be a problem.

A another fisherman, an ice chest full and the increased load will pull the RPM down.

I wouldn't worry about it as adding prop pitch could over-load that motor once you get any weight added. Over-loading a motor as FAR worse than a small amount of RPM.