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1997 Mercury 115

F

floridaorange

New member
Howdy!

Recently bought a 1997 sea ray with a 115 mercury motor. Took it out roughly 10 times and it went into safety (limp) mode on our last outing.

I use regular gas which I now know is a major no-no. The motor was rebuilt last yr $3k, by previous owner. I assume the fuel delivery system is original and i am not sure if it has a water fuel filter or not.

My question is, am I in for a lot of trouble with this setup - should I have it fixed and sell it? Spend more on something newer? I grew up around new boats - uncles had - but otherwise my immediate family did not own a boat. I am handy to a degree but prefer to defer to spe******ts vs trying to fix things I’m new to. Anyway, we have 2 young boys under age of 10, I want them to enjoy long days on the water with the family but don’t want to spend a fortune. Florida, as you can imagine has a pretty massive used boat market - and I’m pretty good at tracking down a good deal, despite the fact that boating is extremely popular right now.

Im not worried about owning this boat, necessarily, but maybe I should be?

Any info you can offer is appreciated - assuming you know what you’re talking about :).
 
Probably something to do with a wonder drug.---My choice for a name would be ----" dixarisen "---There is a little bit of humor for today.
 
The engine does not have a limp mode but it does run on the 2 bottom cylinders from idle up to about 1800 rpm before running on all 4 cylinders.
 
Define limp mode. What is the max rpm you get when the power is reduced? Pull the fuel filter white plastic, fuel lines connect to it, about 3-4" long Port (traffic) side of the engine...can't miss it. Cut it open and report back. If you find it clogged with tan crystaline material that's fuel line to the the engine proper. If little black specks that's internal to the engine fuel line degradation.

Where I am headed with this is that if the main filter is clogged, then the filter for the "reduced power cylinders" is probably clogged also since it is finer mesh and part of the slow speed function designed to keep the fuel flow to 3 and 4 reduced until enough fuel pressure is built up...through increased RPMs for the the fuel fed to 3 and 4 to combust and bring those two cylinders on line. That filter is behind the engines oil tank, toward the rear, up about 1/3 the length of the tank from the bottom. It too is white, smaller than a US Dime coin and about an inch and a half long.
 
Wow ok good to know thank you!
I’m taking it to a guy today - he’s honest and
if it’s a simple fix won’t charge me crazy prices.
Will report back.
 
Nope.-----The low speed circuit on the bottom 2 carburetors only allow a wee bit of fuel in at idle.---Enough for cooling / lubrication but not enough to support combustion.------Fuel pressure does not change.----At 1800 RPM and higher the air flow through the venturi gets the high speed circuit working !
 
racerone said:
Nope.-----The low speed circuit on the bottom 2 carburetors only allow a wee bit of fuel in at idle.---Enough for cooling / lubrication but not enough to support combustion.------Fuel pressure does not change.----At 1800 RPM and higher the air flow through the venturi gets the high speed circuit working !
Click to expand...

Yes, you are correct, had my cylinders backwards, same premise however.
 
racerone said:
Nope.-----The low speed circuit on the bottom 2 carburetors only allow a wee bit of fuel in at idle.---Enough for cooling / lubrication but not enough to support combustion.------Fuel pressure does not change.----At 1800 RPM and higher the air flow through the venturi gets the high speed circuit working !
Click to expand...

The Specifications sheet, Page 1A-4 specifies 3 1/2# fuel pressure at idle and 6 PSI at WOT... I think that is an increase in fuel pressure!!!! Going to page 3B-39, is a diagram of fuel flow and pressure within the 4 cyl engine. For the diagram, they decided on using an RPM that generates 5 PSI of fuel pressure from the fuel pump, 5 PSI fuel enters #1 Carb., output is 4.5# sent to Carb. 2, which drops the pressure to 4#, it sending pressurized fuel to 3 and 4 and also to the accelerator pump which squirts a high pressure (11-14 PSI) blast of fuel into 3 and 4 to get them going as a result of the operator rapidly advancing the throttle. The Accelerator pump is a diaphragm device shaft operated from a cam on the throttle linkage. The faster the operator runs the throttle through the activation range....1800-2000 RPM for a number, the harder/faster the force on the diaphragm and the higher the pressure of the squirt.

Once the throttle stops or is rotated above the activation speed, the pressure in the activation line drops to 3.5# (for 5# at the pump outlet). Any fuel remaining in the activation line is returned to the inlet at the fuel pump inlet...along with new fuel coming in from the fuel tank, which is running with a slight negative inlet pressure due to its sucking action.

Where people have problems with the 2+2 is lollygagging around in the transition zone. Seems to me, with the accelerator pump addition, it was designed to be rammed through that region. On my boat I like to run 3000 rpm which puts me at a comfortable 20-25 MPH speed. To get there I advance the throttle rapidly toward the firewall but not touching it....never measured it......as the boat comes up on plane, I slowly retard the throttle in a synchronous movement with the boat planing out and settle down at my 3000 RPM. I don't have transition problems!
 
That’s very interesting indeed…as this issue only occurred after letting my wife
drive the boat and pull me on a wakeboard. She has no experience driving boats and likely accelerated wrong, one too many times. If that is what caused the issue, what might have happened?
 
Have to think about that a minute. There really isn't anything to hurt physically. Engine just doesn't respond as designed. If anything, you might foul one or both lower plugs but plugs usually clean up with some WOT running for a bit....if you were running excessively at the lower speeds.

Couple of plugs cost a few bucks....change the bottom 2. Take it out and run it and report back.

One thing I do, I learned from Mercury in the design of their 1959 20 hp and lower engines and that was if you are going to putt around a lot on 2 cylinders, tilt the powerhead up in the rear 10-15 degrees. The engine will run smoother and the opportunity for the bottom plugs to foul will be reduced. I practice this myself and it's not rocket science. I can be putting along and watching the engine wobbling back and forth a little bit, just trim it up as stated and immediately, immediately, it quits wobbling and runs smooth as silk...could put a glass of water on top of the cowl and not spill a drop......With the engine tilted down in the rear, unburned fuel...which is what is in 3 and 4 before they light off and produce power, and apparently in 1 and 2 since they are doing the running at low speed, fouls the plugs. Tilt the engine up and I don't know where it goes....gets blown out the exhaust port I guess but the difference in idling and the difference in response when you are through putting and punch it out is noticeable...no slight hesitation, just raw power and away you go.
 
I pulled out all 4 plugs - they were dark but didn’t look fouled. Is it normal to not be able to recognize a fouled plug by looking at it when it comes to these motors?

Also - should i religiously use ethanol free gas? I have fuel stabilizer - is that good enough?

Thank you all
 
floridaorange said:
that’s very interesting indeed…as this issue only occurred after letting my wife
drive the boat and pull me on a wakeboard. She has no experience driving boats and likely accelerated wrong, one too many times. If that is what caused the issue, what might have happened?
Click to expand...
uhh no
 
floridaorange said:
I pulled out all 4 plugs - they were dark but didn’t look fouled. Is it normal to not be able to recognize a fouled plug by looking at it when it comes to these motors?

Also - should i religiously use ethanol free gas? I have fuel stabilizer - is that good enough?

Thank you all
Click to expand...

Sloppy wet and dark grey. Normal plug insulators are tan and dry but that's when you just got through with a good moderate to high speed run and the engine is at operating temp. On this engine the plugs fire all the time but there isn't enough fuel to generate the bang at low speeds so there isn't the heat of combustion to dry things out and develop the color. They're only a few bucks apiece so it wouldn't hurt to eliminate that question.

On gas I have/had a 90 triple and current 115 4 banger. Both 2002 models. The 90 I bought at 2 yrs old and ran E10 and had black internal fuel line degradation at 10 years of ownership. The 115 I bought at 17 years of previous ownership running gasoline a couple of years ago and there isn't any noticeable degradation...running a cotton swap up a hose comes out fairly clean with no tiny chips of black like I had on the 90 and clogged a high speed jet in one of the carbs. I ran Sea Foam at 1 oz per gallon for that 10 years and when I bought the 115 I found an empty bottle of Mercury 1 fuel stabilizer the PO was apparently using so that is what I continued to use in it. Both engines seemed to have the original fuel filter and internal fuel lines when purchased.
 
I think this idea of fouled plugs due to idling / trolling is miss-understood.----I have trolled for hr after hr with V-6 Johnson 235 HP and no issues !
 
My plan is to install the new plugs - take it out to
see if it helps.

It’s got ethanol gas in it - half tank - if I have stabal in it - can i add non ethanol gas to the tank?

Im thin gonna bring it to a spe******t to have all new fuel lines and water/fuel filter installed.
 
floridaorange said:
My plan is to install the new plugs - take it out to
see if it helps.

It’s got ethanol gas in it - half tank - if I have stabal in it - can i add non ethanol gas to the tank?

Im thin gonna bring it to a spe******t to have all new fuel lines and water/fuel filter installed.
Click to expand...

Mixing types of gas isn't a problem. Good idea on having old parts replaced....include a fuel pump kit and have the mechanic cut open your fuel filter and tell you what he finds in it and how much.....is it the original or do you know...does it look like the original? Might have kits put in the carbs too if you never did that, and an impeller in the water pump...if you never did that. Might have him drain and refill the lower unit oil also.
 
Turns out I had some wires that were getting melted toward the top of the motor. The boat is at the shop now with an old school bad ass boat mechanic - he’s already taught me things about how this particular motor likes to be started and i will update once I learn more.
 
Well I'll tell you one thing. When you clear the no wake buoys and want to get up on plane (The Hole Shot) or have a skier behind you ready for the get-up, FIREWALL the throttle from idle in F gear, and then when the boat speeds gets close to where you want to run, cut the throttle back to accommodate that speed......course if you have a skier in tow, you don't want to cut it back too fast....plan farther ahead. Grin. You will be much happier with it's performance.
 
Update - I learned that regardless of the motor starting right up I need to always prime the motor... I was not doing that. I also learned to trim some when idling to let the exhaust exit vs re-enter through the front of motor. Additionally, the voltage regulator was replaced, and the wiring in motor was all replaced, the connections to the battery replaced, and the rev limiter went bad while it was being tested, so that was replaced. Spark plugs were replaced, although the ones that were in there did not look bad.. since I bought new ones anyway, went ahead and replaced.
 
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