# 2002 Merc 40hp - Motor Starts then Bogs and Dies



## Action Johnson (Feb 4, 2016)

Hello, 

Running back on a fishing trip this past weekend my motor started messing up on me and then completely died and I've been trying to diagnose it. I'm looking for some additional ideas/advice. Since this motor is relatively simple I must be overlooking something. 

2002 Mercury 40HP 2 Stroke - SN-0T416108

*Symptoms leading up to now*
-Running back at the end of a day, about 20 mins into the run the motor bogged then went right back to normal RPMs
-the motor bogged a few more times along the run, more frequently over maybe a 10 min period
-Motor bogged down and died and would not restart, I flooded it the first time trying to get it to restart. 

*Current Symptoms*
-Motor will idle for less than 1 min, typically only 10-30 seconds and bogs down and dies
-Motor does not care if throttle is applied or at idle when it bogs down and dies
-Motor starts right back up easily and the process of bogging after a few seconds and dies repeats

*Things ive looked through/Ideas*
-Fuel pump is operational from what i can tell. 
-Fuel Filter is debris free.
-Spark plugs are fine/replaced and getting spark while the motor is being turned over
-Carbs seem fine
-While idling its not spitting fuel back out of the carbs so I'm assuming the reeds are fine
-Voltage at battery when idling is 12.06v
-_It looks like the yellow wires coming out of the stator down to the voltage regulator had got hot enough to melt at the connections - i do not know how long its been this way.
-I repaired this connection and it seems like the motor fired up easier but still dies after the few seconds_


Is there a good method of testing whether the voltage regulator or stator are bad? Is the symptom I've described sound like an electrical issue?

Thanks in advance for the help. I will update if I think of anything else that may give clues!


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## Smackdaddy53 (Dec 31, 2012)

Process of elimination.

Run it on a portable tank with new fuel hose/primer bulb and see what it does. This will eliminate everything up to the outboard if it persists. If it continues then you can focus on the fuel tank to the end of the fuel hose that connects to the outboard.


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## topnative2 (Feb 22, 2009)

ck fuel/water seperator
ck primer bulb
dump carb fuel bowl into a glass jar look for h20


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## Jred (Sep 22, 2013)

You say carb seems fine but what you’re describing the carb does not seem fine. I would pull it off and clean it and do new gaskets


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## southerncannuck (Jun 27, 2016)

I’d start with Smackdaddy’s advice. I had the same issue. Turned out to be the fuel line disintegrated internally and would block the fuel flow. 

You can disconnect the gas line fittings and visually check. Problems with the inner sheath will be obvious.


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## mwolaver (Feb 6, 2014)

Jred said:


> You say carb seems fine but what you’re describing the carb does not seem fine. I would pull it off and clean it and do new gaskets


carbs were a recurring problem with my 2 strokes. You cannot "look" in there and see the issues. The bowls need to be removed and jets cleaned/replaced. What was happening in my case: little "bb's" of varnish or semi-viscous material would float around in there and eventually get sucked up on a jet. It was intermittent and frustrating. Use non-eth fuel!

Totally agree with 1st step: run it with a portable tank....


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## Action Johnson (Feb 4, 2016)

Smackdaddy53 said:


> Process of elimination.
> 
> Run it on a portable tank with new fuel hose/primer bulb and see what it does. This will eliminate everything up to the outboard if it persists. If it continues then you can focus on the fuel tank to the end of the fuel hose that connects to the outboard.


I will give that a shot to eliminate some more things!


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## Action Johnson (Feb 4, 2016)

Jred said:


> You say carb seems fine but what you’re describing the carb does not seem fine. I would pull it off and clean it and do new gaskets


I assumed that the carbs were fine since it starts up quickly and easily. I went ahead and ordered rebuild kits, they need to be done either way!


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## Smackdaddy53 (Dec 31, 2012)

Action Johnson said:


> I assumed that the carbs were fine since it starts up quickly and easily. I went ahead and ordered rebuild kits, they need to be done either way!


Starting and sustained running are totally different with carbed outboards.
Buy OEM kits and make sure to clean the carbs 110% and you’ll at least be that far ahead.
I like ChemDip in the gallon can. Soak all metal parts in it 45min-1hr and finish cleaning and drying with Carb Cleaner. Be careful with jets, clean out with copper wire so you don’t enlarge the hole or gouge it.


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## TylertheTrout2 (Apr 21, 2016)

Action, I have a similar Merc (2000 50hp 2 stroke) and the carb job is pretty easy. Get some of that air blaster in a can to help blow the shmeg out of the jets. Good chance that could be a part of your issue and good to do either way, like you said!


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## Smackdaddy53 (Dec 31, 2012)

TylertheTrout2 said:


> Action, I have a similar Merc (2000 50hp 2 stroke) and the carb job is pretty easy. Get some of that air blaster in a can to help blow the shmeg out of the jets. Good chance that could be a part of your issue and good to do either way, like you said!


Varnish builds up inside the jet tube and changes the diameter causing issues with how much fuel flows in when the float falls. The jets are finicky and need to be clean to work. Air is not going to clean the varnish out. A ChemDip soak will.



chem dip - Google Search


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## Mike Haydon (Dec 19, 2019)

I'm with everyone on using a new portable can and hose and bulb. That will eliminate all that. Also some of those electrical components you mention only deal with charging, the starter would be ok to check off the list. Honestly it sounds like floats are bad or jets are clogged. You get it running because you fill them up then it burns that off and dies. 


Try cranking it and see if pumping the primer bulb periodically will jeep it running.


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## Action Johnson (Feb 4, 2016)

Smackdaddy53 said:


> Varnish builds up inside the jet tube and changes the diameter causing issues with how much fuel flows in when the float falls. The jets are finicky and need to be clean to work. Air is not going to clean the varnish out. A ChemDip soak will.
> 
> 
> 
> chem dip - Google Search


ordered OEM carb repair kits, they will come with new jets, also picked up that chem dip bucket you linked to. Thats a great idea.


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## Action Johnson (Feb 4, 2016)

Mike Haydon said:


> I'm with everyone on using a new portable can and hose and bulb. That will eliminate all that. Also some of those electrical components you mention only deal with charging, the starter would be ok to check off the list. Honestly it sounds like floats are bad or jets are clogged. You get it running because you fill them up then it burns that off and dies.
> 
> 
> Try cranking it and see if pumping the primer bulb periodically will jeep it running.


It will die whether you are pumping the bulb or not.


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## Smackdaddy53 (Dec 31, 2012)

Action Johnson said:


> ordered OEM carb repair kits, they will come with new jets, also picked up that chem dip bucket you linked to. Thats a great idea.


That ChemDip will last you years.


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## Mike Haydon (Dec 19, 2019)

Action Johnson said:


> It will die whether you are pumping the bulb or not.


I'm sorry bud, should have said try the primer bulb once you get the fuel tank and new hose and bulb. Then see if it helps.


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## Kamtam (7 mo ago)

Action Johnson said:


> ordered OEM carb repair kits, they will come with new jets, also picked up that chem dip bucket you linked to. Thats a great idea.





Action Johnson said:


> It will die whether you are pumping the bulb or not.


This is pretty common with these older mercs. I go through this at least every six months. Carb and gas issue. You're on the right track


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## Tarponhead (Mar 18, 2018)

All good advice here. Definitely get a trash can and run it in there, that will save you a ton of time. 
There are a number of things you should go ahead and do if they havent been done since you bought the engine, as its got 20 years of life on it. Check compression first to make sure all good there, it probably is. You know you want even (less then 10% differential) between the cylinders, and probably somewhere around 100psi.
1) rebuild the fuel pump. If it has just a pin hole in the diaphram it wont keep up with the carbs needs and eventually die. Any porosity prevents proper pressure. Be sure there are no folds when you install the diaphram. 
2) time to replace the fuel lines. On the engine, and all the way to the tank. It is correct they can disintegrate internally and trash up everything. Newer fuel lines have a “liner” in them. Early iterations, that liner would loose the attachment to the outer hose, and then collapse causing a restriction, and starving the fuel supply. I have found this usually happens at the center of the hose, not where you can see it. Cut the old hose length wise to investigate. When installing the new hose, be careful not to push the liner down into the hose causing a restriction. Lightly grease the hose fittings they slip over before installing. 
3) clean the carbs as discussed. Be sure to count the turns the idle mixture screw takes to LIGHTLY seat ( clockwise to seat ). write it down and reset to that when you rebuild it. Use carb cleaner in a can to spray into the passages (I use CRC from NAPA), and finish with a light blast of air from air compressor. Set the new float to spec, closed and open dimensions. 
4) inspect the reeds if you can when carb is off. They are probably good as you stated. 
5) replace fuel/water separator. After replacing this and the fuel line, check that all connections are free of sucking air by using a Mighty Vac. Pull a vacuum, and see if it will hold it for a minute or so. 5-7inHg should be enough. Dont suck gas into the gage or you will be buying a new one. Remember, if a fuel line does not fit a fitting snuggly, any amount of clamping will not seal it, keeping it from sucking air. ABYC standard is to use 2 hose clamps with the screw rotated 180* apart, to prevent air gaps. I use Oetiker clamps that are capable of clamping the full 360*. 
6) Its probably not due to the stator wiring, since it starts easily and runs for a short time. But to fix those wires, cut and slip heat shrink around them, shrink it up, leave some wire color showing on the good end in case you have to troubleshoot in the future. Use a good marine grade connector like Ancor. That most likely happened due to a loose or dirty/corroded connection. Check the ground to the circuit also. Clean real good, make sure the connection is tight, and liberally paint all connections with Dielectric Grease (silicone). You can also use Evinrude Corrosion Inhibitor. Check every connection every time you change plugs (yearly). 
7) Install new spark plugs, not the problem here, but might as well. Gap them to spec, I have noticed most plugs you buy today are not consistently gapped out of the box as they use to be. 
There is only one other thing it could be ( but I seriously doubt from the symptoms you state) is worn crank seals not allowing enough vaccuum internal to the crank case. I seriously doubt this, since it starts and runs well for a period. The symptom typical for this is very hard to start, and cant get high RPMs. I say this for future reference for you, but dont worry about it until it happens. I have 2 engines of the same vintage and have never changed the crank seals.
Do all this and you should be good for another 10+ years. 
Good luck, take your time, be meticulous on everything. 
My 2 cents


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## Tarponhead (Mar 18, 2018)

Report back your finding so others can utilize this thread in the future.


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## matauman (Nov 4, 2014)

Thank you Tarponhead, I have a similar engine and plan to print your post and put in my manual. Although I hope that I never need it!


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## Tarponhead (Mar 18, 2018)

matauman said:


> Thank you Tarponhead, I have a similar engine and plan to print your post and put in my manual. Although I hope that I never need it!


Imo, you should change fuel lines all the way to the tank every 10 - 15 years. If you use ethanol gas, more often. Dont forget the supply hose to the tank if you have an external filler.


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## topnative2 (Feb 22, 2009)

I was told along time ago by the best mechanic I know and I proved it to myself.......always soak the carb in cleaner when doing a rebuild...Smack has it together once in awhile


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## Action Johnson (Feb 4, 2016)

Tarponhead, thanks for the advice, I am going to take that entire list and do those items as well as what Smack already suggested. I will report back with my findings once everything comes in and I have time to sit down and do all of these things!


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## matauman (Nov 4, 2014)

Totally, Smack delivers great advice, mixed in with a very witty repartee!


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## Action Johnson (Feb 4, 2016)

Small update...

Got around to pulling the carbs and rebuilding them. There was some minor buildup in some of the jets and orifices' but overall the carbs were very clean. They got a full spa treatment so we will see what that does. Ill be rebuilding the fuel pump this week while waiting for all new fuel lines on the motor and from the fuel tank back. 

All cylinders had 130psi compression as well. 

Hopefully ill have a running report here soon.


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## Tarponhead (Mar 18, 2018)

With the age of the engine, its a good idea to do the carbs anyway. 130 psi tells you its in excellent health, as far as compression goes. Once you get it figured out, it will be like a new motor with those numbers.


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