1994 Mercury 100hp Trouble Starting and Constant Alarm

eric15k

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Jul 14, 2015
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I recently bought a boat with a 1994 Mercury 100 hp outboard serial number 0G050058. Previous owner stated the boat had not been ran in a year. Everything sounded and worked great while running on muffs.

First time I had the boat out everything ran great, no alarms, but after we stopped for a short time and tried to restart the engine it would die at idle, solution to this was to use the high idle and then quickly shift into gear after bringing it back down to idle. This problem only occurred once during the first trip.

Second trip, after leaving the dock a constant beep alarm came on, from what I've read this is the overheat alarm. The engine had only been on for a couple seconds so I don't think there is any chance it was overheating. The alarm went off after about 30 seconds of idling. Ran the engine for a couple hours with no problems. Later in the day the alarm came back on while idling, as well as after letting the engine sit without being run for about 30 minutes with the key in the on position and the engine off. Also the same problem I had the first trip with trouble starting happen twice during this trip. Decided to call it a day and while heading back to the ramp the engine lost a noticeable amount of power, it sounded and felt like not all cylinders were firing, the power would intermittently kick back in, the increase in power was noticeable. The alarm was not on when this happened. Eventually the power came back and everything felt fine. While idling before loading the boat at the ramp the constant alarm came back on.

From what I've read the trouble starting could be that the carburetors are gummed up, would this also explain the short loss in power? What about the constant alarm? This is my first boat/outboard, I am quite mechanically inclined but have zero experience with outboards or boats in general. I'm planning on checking the compression tomorrow and checking the spark plugs. I have looked for carb rebuild kits but can't find one for this engine that includes the floats and needles, maybe I am looking in the wrong place.

Carburetor kit I found, will this work and would I just reuse the old floats/needles?

http://www.iboats.com/mall/partfinde...n_id=068850564

I am also planning on ordering the service manual. Is this the correct manual for my engine?

http://www.iboats.com/Mercury-Marine...view_id.272598

If anyone could give me any insight as to what is happening or any guidance it would be greatly appreciated.
 
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Texasmark

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Dec 20, 2005
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14,544
Gummed up fuel problems are probably a given. Check the entire fuel system for varnish or foreign objects like fuel line particles where the fuel line has deteriorated internally. Use a good carb cleaner like Berryman's Chem tool when doing the kits and plenty of high pressure air. Disconnect the fuel line at the engine (if you can) and if a removable connector, use a popsickle stick to depress the ball in the female end (hose to the tank) and using a clean, clear preferred, container, squeeze out some fuel an see what you have in the line besides clean fuel. A good dose of Sea Foam in your fuel at least for the first few outings will certainly help to solve sit up problems.

On the OT, I agree that you have a problem somewhere that is not temp related. That engine has 2 warnings, and 2 methods of cooling the engine. The solid tone is the OT sensor on the back of the block not far from the spark plugs. Wire to it is tan or tan with a light blue stripe. If the OT sensor closes, it grounds one side of the alarm and it sounds, 12v from the key (red wire purple stripe) is power to it. The normal closing temp is 195F.

Your cooling is a thermostat which starts opening at 143F and when you get your rpms up to around 2500 there is a larger pressure regulated valve (poppet) that opens and allows full flow of cooling water through the block. The tell tale water column is plumbed off the exhaust manifold and is not part of the engine cooling loop so just because you have "pee" you don't necessarily have adequate cooling.......not related to your problem but let you know anyway.

I agree with you that you didn't have a real OT condition. What I'd do on that problem is follow the tan wire from the sensor to the bayonet coupling where it connects to the wiring harness from the control box, within the engine, right side (starboard) of engine. Disconnect it. It is hard to disconnect so expect resistance, but just grasp as carefully as you can with a couple of pair of pliers and work it free. Leave it off for you next outing. If you have no more OT alarms, your problem is a bad sending unit......at the end of that tan wire embedded in the rear of the block, held in with one screw, in the water jacket. If you get another alarm with that line disconnected, then you have a wire shorting out somewhere and it will be the tan wire back to the control. Depending on whether you have a Commander 2000 or 3000 control, it could be inside the control or tie wrapped to the wiring harness right at the location of the control. The horn is black and about the size of 3 half dollars in a stack.
 

eric15k

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Jul 14, 2015
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I checked the fuel at the connector that goes into the engine and there are a good amount of particles in the gas. I checked the compression and all cylinders are 124-127 psi. I checked the engine temperature with an IR thermometer after idling for 15 minutes, top 2 cylinders were around 125 F, lower two cylinders were around 120 F. The water stream wasn't very warm which I assume is because the engine wasn't warm enough for the thermostat to open. It was idling around 1700 rpms, I assume this is because it's on muffs and not in the water. No alarms went off while idling on the muffs.

Tomorrow I plan to vacuum test the fuel line and check for air. At this point I am probably going to go ahead and replace all fuel lines and clean or replace everything I can that is involved in the fuel delivery system. Also while I'm at it I'm considering adding a fuel water separator as this boat doesn't have one.

As far as using the Berryman's Chem tool, I read this in another thread:

"Berryman Chem Dip works but it will remove the Alodine that's been keeping them from corroding for all these years. Just use Gunk Carb cleaner."

From this thread: http://forums.iboats.com/forum/engi...1-1988-mercury-100hp-carburetor-cleaning-help

I have not been able to find anything else about this problem with Berryman Chem so I'm thinking that this is just one person's belief on the matter but would like to get a second opinion before using it.

As far as the alarm I am going to do as you said and disconnect it the next time I'm out, as well as monitor the engine temp with an IR thermometer.

I haven't researched it yet, but figured I would ask, would it be a very difficult task to add a digital temperature gauge to this outboard? Would it be worthwhile?

Just for reference if anyone comes across this in the future, I found the service manual for download at this link: http://mercury-2-stroke.marineservi...-1848cc-2-Stroke-Outboard-Service-Manual.html
 

Texasmark

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Dec 20, 2005
Messages
14,544
I checked the fuel at the connector that goes into the engine and there are a good amount of particles in the gas. I checked the compression and all cylinders are 124-127 psi. I checked the engine temperature with an IR thermometer after idling for 15 minutes, top 2 cylinders were around 125 F, lower two cylinders were around 120 F. The water stream wasn't very warm which I assume is because the engine wasn't warm enough for the thermostat to open. It was idling around 1700 rpms, I assume this is because it's on muffs and not in the water. No alarms went off while idling on the muffs.

Tomorrow I plan to vacuum test the fuel line and check for air. At this point I am probably going to go ahead and replace all fuel lines and clean or replace everything I can that is involved in the fuel delivery system. Also while I'm at it I'm considering adding a fuel water separator as this boat doesn't have one.

As far as using the Berryman's Chem tool, I read this in another thread:

"Berryman Chem Dip works but it will remove the Alodine that's been keeping them from corroding for all these years. Just use Gunk Carb cleaner."

From this thread: http://forums.iboats.com/forum/engi...1-1988-mercury-100hp-carburetor-cleaning-help

I have not been able to find anything else about this problem with Berryman Chem so I'm thinking that this is just one person's belief on the matter but would like to get a second opinion before using it.

As far as the alarm I am going to do as you said and disconnect it the next time I'm out, as well as monitor the engine temp with an IR thermometer.

I haven't researched it yet, but figured I would ask, would it be a very difficult task to add a digital temperature gauge to this outboard? Would it be worthwhile?

Just for reference if anyone comes across this in the future, I found the service manual for download at this link: http://mercury-2-stroke.marineservi...-1848cc-2-Stroke-Outboard-Service-Manual.html


Alodine is a corrosion chemical applied to aluminum to prevent corrosion. It acid etches the aluminum and id doing so leaves a protective coating similar to how surface rust helps to protect steel from further rusting. I have used Berryman's Chem tool for 50 years and have used Gunk products. I personally don't like any of their products as they leave a slimy film on everything whereas Berrymans has the chemicals to cut through varnish and evaporates leaving your parts clean and dry. I prefer the spray, not the liquid. It's quicker and if you apply it in a couple of coats, letting the first soak in, it powers away the contamination in the little crevices that you can't get to with a brush. To each his own on that.

Engine temps you first mentioned are great and I share your analogy. Also great that you are taking your IR with you. The Tstat pellets on all the Mercs I have been into is 143F for opening temp and give it 15 degrees more to be full open. Below 2500 rpm (service manual number) the stat controls the block internal temp. Over that water pressure opens a popoff valve, much larger in diameter, that allows significantly more water through the powerhead for increased cooling and essentially bypasses the stat, regardless of the water temp internal to the powerhead.

Once you do your run and take your temp measurements, you can concentrate on a faulty alarm/alarm wiring. Looks like an open and shut case.

Good luck and let's hear back.

Mark
 

eric15k

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Jul 14, 2015
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Right now I'm waiting to receive the carb/fuel pump kits, fuel lines, and fuel filter. I removed the old fuel lines and pump, and they appear to be in good condition, emptied the gas tank, cleaned it out, there was a good amount of debris in the bottom.

Something I noticed while looking over the engine is that there are no lines connected for the high speed stator, is that something I should be concerned with/look into further? The service manual shows that there should be red and red/white wires connected here for the high speed stator. The only lines I can find coming from the stator are 2 solid yellow, and green/white and white/green which turn into the blue/white and blue.

hDItsw7.jpg?1.jpeg
 

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Texasmark

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What high speed stator? The rectifier/regulator input are the yellow wires. The green white are triggers from the trigger pick up coils under the flywheel, trigger stator. I don't have my serv man any more so I am at a loss on the red white. Only red in the engine has always been 12v distribution and if it's after the ignition key it's red with a purple stripe or just purple. The blue white was oil reservoir alarm on my last engine and went to a modulator which caused the beep to be a square wave, not a constant solid beep which is the OT alarm on the tan wire. Purpose was to tell you which alarm was beeping. Just because the green and blue are in the same vicinity on the switch box, don't get them confused.

Just dawned on me what "high speed" red wires are. How about when rpms are above 2500 rpms and your other two cylinders kick in, this would be the triggers. Geez I wish I still had my serv. man. I don't remember if all 4 cyl got triggers all the time or not. Don't remember if the control of the other 2 cyls was fuel only. I remember reading about them being supplied with enough fuel for lube, but not enough to ignite below 2500. With that it seems you would have triggers on them continuously.
 

eric15k

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Jul 14, 2015
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Sorry, I should have deleted that post. I found my answer. The section of the service manual I was reading was about a different model stator. My engine has the red stator with only one set of wires, not low/high. I tested the ohms on the stator and it tested within range. I will be rebuilding the carbs and pump this weekend and hopefully have the boat out sometime next week. Thanks for all your help.
 

Shawnmm

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Jul 24, 2015
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I love this engine. It can be a little picky sometimes but every boat I have ran with one rockets when all 4 cylinders kicks in. Ya, all four cylinders have full time spark. I think once you get the issues worked out, you will really like it.
 

eric15k

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Jul 14, 2015
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Alright here's a list of everything I've replaced/cleaned:
-Carbs
-Fuel Pump
-Fuel Tank
-Fuel Lines
-Primer Bulb
-Added fuel/water separator
-New Fuel tank vent (old one didn't have a screen, allowed junk to get into the tank)
-New Fuel tank sending unit (old one was corroding badly)
-Thermostat
-Poppet Valve
-Impeller

The carbs looked absolutely spotless, looked like they had just been rebuilt so I am doubting that was the problem now.. But regardless I cleaned them and replaced the gaskets since I already had the kits. The fuel pump gaskets did seem a bit worn but not to the point of failure, that was also cleaned and components replaced.

If the issue was related to fuel delivery it should hopefully be solved now. I replaced the water/cooling components just because I don't know when it was last done and it's cheap and easy insurance.

Fired right up on the first try, idling great on muffs. No alarms, although I had no alarms before on muffs. Now if there will just be a day below 100 I will get out on the water and test it out.
 
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eric15k

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Jul 14, 2015
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Does anyone know if it's possible to add a water pressure gauge to this engine? If so, where would it be attached? I know this question is unrelated to the original thread post, if I should start a new thread I will gladly do it.

Also, what is this brass plug for on the cylinder cover? I can't find any mention of it in the service manual. Is this where a water gauge would be hooked up?

image_226871.jpgimage_226870.jpg
 
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eric15k

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Jul 14, 2015
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That where you hook up the water pressure guage....

Awesome thanks. I've been looking everywhere in the service manual and couldn't find anything on it and looking at the diagrams it didn't seem like that was where you would hook it up but it makes sense.
 
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