Starting a Mercury 115HP That Has Been Sitting

Laker99

Petty Officer 3rd Class
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Feb 27, 2013
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I am thinking about buying a 1987 Mercury 115HP that has been sitting for six years. The motor had just been tuned up and had a carb rebuild 6 years ago. The mechanic that did the work said it was completely gone over and was completely fine when it was parked. It was parked outside, uncovered, and never touched. I took the cowl off the motor and it looks very clean. The motor looks very good from the outside too. Great paint, skag and the prop looks like new. How would I go about starting this motor? I was thinking that I should probably pull out the spark plugs and spray fogging oil in and then turn it over. I could do the same thing with the three carbs. I will check the lower unit fluid. And, of course, I will get a tank of premium, no-ethanol fuel with some Sea Foam added. Should I use starting fluid if it doesn't fire at first? I'm pretty certain that someone who knows what they are doing could get this thing running. I wish I knew more about motors but I also don't want to pay a mechanic $90/hr to trouble shoot this.
 

Bosunsmate

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Apr 7, 2012
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Re: Starting a Mercury 115HP That Has Been Sitting

Yep do what you said, but try not to use starting fluid if possible as it can seize it.
Id also prime it with fuel, then drain the carb bowls so that anything in the lines thay may have come lose wont block a jet
 

emckelvy

Commander
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Re: Starting a Mercury 115HP That Has Been Sitting

Don't use starter fluid, it has no lubrication in it and is bad for the motor's innards. You can pour some 50:1 pre-mix in a spray bottle, then carefully spray that in the carbs if it doesn't want to fire readily.

This motor does have an enrichening system, rather than choke shutters, so as long as you pump the primer bulb firmly, then crank over while pushing the key in (or pushing a choke button if you have that type of control box), it should spray fuel directly. Hopefully they drained the carbs when it was put away.

It certainly won't hurt to spray a bit of fuel in the carb throats to start out with.

Do you know if the impeller was replaced before the motor was layed-up? If so, the blades would be curled-up somewhat but there should be no fear of breakage.

Otherwise, and especially if you don't know the history of the pump, I'd go ahead and drop the lower unit and renew the impeller before you even try to start it for the first time. Definitely before you go out on the water.

Cheap insurance, and if an old impeller blade were to break and get pumped up into the system somewhere, you'll have a lot more work tearing things apart (including a possible powerhead & covers removal) to find the errant chunk o'rubber!

Unless the mechanic replaced the fuel pump diaphragm/gaskets when the carbs were rebuilt, there's a possibility they could be dried out and not function properly. You can give it a try for the initial startup, but I'd recommend installing a diaphragm kit before going out on the water. There are 2 different styles of pump, the older long-style with roundy-ends, and the newer square-style. Be sure of what style you have before ordering parts.

Also check fuel lines for deterioration, they're 26-years-old (doesn't time fly??)! They can look good on the outside and be bad on the inside, sending chunks of rubber to plug up the carbs.

Check all the large and small rubber lines, fuel or otherwise, for cracks, splits, etc. Many of the lines connect to the crankcase and if they leak, it'll suck air into the crankcase and lean out the mixture.

If the lines look like new and are nice and flexible, that's a good sign.

And yeah, if you can get non-ethanol fuel, by all means use it! Ethanol is Bad Stuff; it tears-up fuel system hoses & corrodes carbs. A real Boon for outboard mechanics but Bad News for the owners!

HTH & let us know how your Tower of Power runs.........ed
 

emckelvy

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Re: Starting a Mercury 115HP That Has Been Sitting

Yep do what you said, but try not to use starting fluid if possible as it can seize it.
Id also prime it with fuel, then drain the carb bowls so that anything in the lines thay may have come lose wont block a jet

That's a good idea, you can remove the main jet plugs and flush fresh fuel thru the carbs and out the main jets. It's the lowest point on the carbs, so anything nasty should come out. Note that the enrichener sucks fuel from one of the carbs, so instead of a main jet plug there'll be a fuel fitting in the hole......ed
 

Mi duckdown

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2,575
Re: Starting a Mercury 115HP That Has Been Sitting

Laker99. First what price for the Motor?
 

Laker99

Petty Officer 3rd Class
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Feb 27, 2013
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Re: Starting a Mercury 115HP That Has Been Sitting

Well, that's the enticing part of this. The guy only wants $500 for the motor. I'm a fairly handy guy but not necessarily with motors. I wish I had the skills you guys have because my gut tells me this is a good motor - especially for someone who knows how to tinker with them.
 

Mi duckdown

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Re: Starting a Mercury 115HP That Has Been Sitting

Laker99 I would buy that motor in a heartbeat. does it come with the controls? Is the mechanic also the seller? and what is compression on the cylinders and what does the lowerend lube look like?
 

mr 88

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Re: Starting a Mercury 115HP That Has Been Sitting

Isn't that year when they changed some of the HP ratings/decals on the Towers,while never changing anything on the inside. The 115 is a 150 in sheeps clothing I think.
 

Laker99

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Re: Starting a Mercury 115HP That Has Been Sitting

Yep. Controls come with it. I don't know what the compression is because I haven't been able to mess with it. I know I could always sell the parts off of it if I needed to. This boat was abandoned by a customer that couldn't pay his bills and the mechanic doesn't want to spend the time filing liens, etc. so he said I can have the motor for that amount if I am willing to do all of the paperwork which will take some time and headache. But I am better at dealing with bureaucracy than I am working on motors. The mechanic would rather work on motors at $90 per hour than try to sort out this mess. He just wants his money for parts and labor from 6 years ago and to get it out of his boat yard.
 

Laker99

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Re: Starting a Mercury 115HP That Has Been Sitting

Isn't that year when they changed some of the HP ratings/decals on the Towers,while never changing anything on the inside. The 115 is a 150 in sheeps clothing I think.

I believe the 1984 - 1988 models are all similar. That was the year they started prop rating horsepower and they updated the trim and ignition. I know the 90HP and the 115HP have many common parts. I have been told if you want one of these inline sixes to try to find a 1984 - 1988 model. I have also heard that the original Merc 1500 (150 HP powerhead rated) was called the Tower of Power but people just started calling all of the inline sixes "Towers of Power." At least that is what I have read! I just like the way they look on the back of a boat and since they all looked similar you can buy decals for whatever year if you want to match the year of your boat.
 

emckelvy

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Re: Starting a Mercury 115HP That Has Been Sitting

1987-1988 year Inlines were the Best of the Best! I'd buy it in a heartbeat for $500, especially as clean as you said. Even if the powerhead was trashed internally, it'd be worth throwing a rebuilt powerhead on it, or rebuilding that one. The pristine-condition lower unit is probably worth the asking price, by itself.

Propshaft-rated 115's were essentially a 140hp crank-rated motor. The late-70's 140hp was more-or-less a 150hp with low-dome pistons (helps with the low-grade gas we have nowadays).

If you wanted to build a Beast of a motor, use hi-dome pistons, and older 10-petal banjo-type reed block assemblies. My buddy the Good Dr. Frankenmerc built a "Frankenmotor" for his Glasspar G3 and it was a real Beast! Quite scary at 60mph when I rode on the lake with him, and he had it up to at least mid-60's by himself. This combo requires a super-high octane fuel or 100/LL Avgas to prevent detonation.

Even stock it'll be a very strong running motor, just feed it lots of good non-ethanol fuel and it'll be happy!

Now we need some pics of this motor, to feed our Inline Tower of Power fetish!!!!

Cheers..........ed
 

Laker99

Petty Officer 3rd Class
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Messages
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Re: Starting a Mercury 115HP That Has Been Sitting

I thought the 1984 through 1988 models are all the same. Are you saying the 1987 and 1988 models are superior to the 1984 - 1986 ones? Also, do you have a recommendation for a shop manual. I want to get one and start reading about these motors. I looked on EBay and hoped to find one specific to this motor. All of the ones I saw were for many models and several years so I wondered if they will have the level of detail I need for this motor in particular.
 
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