Outboard bogging down. Take a look, tell me what you think.

First off I am not very good mechanically. I know very little about engines big and small. My ‘93 mercury 40hp 2 stroke oil injection outboard boggs down intermittently. Also it seems to be using a lot of gas in my opinion. I have nothing to base this off of but to me I would think a 6 gallon gas can should last longer than 1/2 of a Day trolling, and running around. Sometimes i crank it up and it whines out, bogs down and only goes about 2/3 max RPM’s. It did this last year when I bought the boat, I didn’t use it much, but plan on using it quite a bit more this year. Since I’ve owned it I’ve only ran non oxygenated 91 octane in it, and previous owner said he ran that in it also. The first tank I filled up with last year I dumped a couple ounces of sea foam in it, and I did the same this year. I winterized it properly, and previous owner said he did the same. When I was cleaning the boat out when I first got it I found a bag of probably 10 new spark plugs in a compartment. So I’m assuming that maybe previous owner may have had something similar, and putting new spark plugs in fixes it temporarily? But I’d like to find the problem and get it taken care of. Other than that everything seems to be working fine, it’s using oil so injectors must be working. Anyways if you don’t mind watching the video if your good with motors and tell me what you think, once I got it up to full throttle I keep it there in the video……

Thanks, Drifter.

Oh and I’m not trying to “click pimp” my YouTube channel. I just use it to post videos here on IDO. It’s the only way I know how to.
Thanks for looking again,Drifter.

My first thought is the power pack. That is definetly not fuel related. You are losing spark completely at times. That could cause fouled spark plugs but the root cause is definetly electrical. I’m not totally sure but you may be able to test or get the power pack tested. Maybe someone here (iowaboy) can verify.

Not sure about the fuel consumption, but I don’t think 6 gallons is unreasonable for a 2 stroke. Especially a mid 90s gas hog Merc.

This was my power pack being bad. At idle it sucked.

I’m no expert but I’d be looking at coils or plugs. Gapped correctly? They do not come pregapped!

I’d take the plugs out first and see what those look like and go from there. When you take em out make sure you remember which plug went to which cylinder for reference.

Seems like spark because it only misses at high rpm and its intermittent. I’m no mechanic though*

I would run new plugs and replace gas lines to start.

well I have seen this before and there a few things that can cause it.
mine acted like that once (95 40hp ) and it only did it after I put new spark plugs in it.
I put non resistor NGK’s back in it and problem solved,for some reason in my experience mercs dont like resisted spark plugs,especially the ones whos name is opposite of loser,they will start hard,idle rough and use a barrel of gas going anywhere.

try that first,if that doesnt work here are some things for you to check out before you go throwing parts at it.
very first thing after putting NGK’s back in it which is a must.( if they arent already in it

1- with the cowl off and it running on a garden hose and muffs,spray the coil pack and wires down with water,if it starts missing you have a bad coil or wire.

2-pull the main electrical connector to the helm apart as well as the other connectors to the ignition box and check it/them for corrosion,it will look like a white residue or powder in the sockets and on the pins,clean it up,put some dielectric grease on it try it again.

3- using the primer bulb,pump it up tight,remove the fuel line from the output side of the pump and install a foot long chunk of fuel line.
run that hose into a coffee can,start the motor and watch the fuel flow.
it should be strong and steady with no air bubbles in the fuel.
if it is weak,the pump needs a kit put in it.
if you see air,you have a leak somewhere in the fuel system between the pump and tank,the pump can suck air as well through its own gaskets.

4- I have seen in rare instances that the voltage regulator will go bad and pollute the electrical signals in the ignition box causing all sorts of havoc with it running correctly.
normally the regulator will either over charge or not work at all and not affect the ignition when it goes bad but it does happen.
it does this when the internal diode fails and allows A/C voltage into the D/C side of things.

5- if you or the previous owner have no idea of when the carbs were cleaned,have that done while you are at it.

it doesnt sound or act like a reed has failed at the moment so I wont go into detail on how to check that out.

my merc is on a 17 foot deep vee that weighs around fifteen hundred pounds,six gallons of gas will run me a day of running wide open,trolling and generally enjoying the day on the lake.
check these things out and report back,I hate to think that the ignition module is bad but it does occur,when they do go bad,they dont tend to come and go like your video shows.

hope this helps you get on your way to a good day on the water !

another thing to check I forgot to add:
look at the wires that come out from under the flywheel,these wires are from the stator that charges the battery as well as charge the ignition module,these are your ignition “switch” wires,nothing to do with the starting switch.
make sure they dont look like they have been hot and melted the insulation on them.
follow them all of the way to the regulator and ignition module,if you find any breaks,melting,etc. the stator needs replaced.
easy enough job but you have to remove the flywheel to get to it.

good luck!

That’s very good advice iowaboy!!! I’ll start with the plugs, but pretty much beyond that I’m in trouble, as I don’t even know what a stator, coil pack, etc. even look like, let alone tear it apart. I’ll most likely bring it in to have it worked on.

Thanks again guys!

I wish I lived closer to you guys as I could teach you how to check things out and do them yourself.
you can only learn by doing and there is nothing scary about any of it,well,unless you get bit by thirty thousand volts at the spark plug wire,that’ll make you pee yourself real quick !!

good luck drifter,let us know what is found out.

Iowaboy1 wrote:

I wish I lived closer to you guys as I could teach you how to check things out and do them yourself.
you can only learn by doing and there is nothing scary about any of it,well,unless you get bit by thirty thousand volts at the spark plug wire,that’ll make you pee yourself real quick !!

good luck drifter,let us know what is found out.

will do. I’ll try the spark plugs this week, if that don’t work it might have to wait till Sunday to work on it. Thanks again iowaboy.

Everything Iowa boy said is good advice.

Personally I think you are intermittently dropping a cylinder, which will lead to fouled plugs, power loss, etc. If it was running like crap all the time, at idle you could figure out which power pack was bad pretty fast. In this case, it might be a bit more difficult.

Best of luck. Nothing worse than not having that motor running right.

Iowaboy1 wrote:

I wish I lived closer to you guys as I could teach you how to check things out and do them yourself.

Stop wishing and start moving! My tilt/trim is still bouncing. 2 rug rats is making it difficult to fix.

I had a similar issue on my 95 75hp merc. After putting 3 carb kits in it, plugs and a glass see through fuel filter in it. I was running it at home and was still doing same thing. Then seen the culprit floating around in the fuel filter while it was running. The gaskets in the 3 piece fuel pump were rotten. The fuel was able to flow between the cavities inside the pump. After $150 the $5 gasket kit fixed it good as new. Good luck.

i would tighten the battery connection with a pliers. and then i would replace every fuel line. then i would dump the gas tank and start over. seafoam every tank.

also, is your fuel tank the new kind that get sucked kind of flat and balloon up in the sun?

iowa_josh wrote:

also, is your fuel tank the new kind that get sucked kind of flat and balloon up in the sun?

Yes it is. But I make sure the vent screw is always open, after a couple issues with this. Lol.

My dad had that exact outboard 2 boats ago. This is the Classic 40, 4 cylinder, correct. Good outboards.

He had a very similar issue, a pronounced miss at most RPM ranges. A miss at higher ranges like that is usually an electrical miss. I did all the stuff that Duchboy recommends and then some, finally took it to a shop. CD pack was going bad and the coil was weak.

New CD pack and new coil, ran great.

Not to discourage you from a DIY fix, but those sudden misses like in your video say “electrical issue” to me and that’s not something that most guys are going to figure out and fix on thier own. Plus, electrical parts are expensive so you don’t want to go on a parts swapping safari and then find out you were on the wrong track.

Grouse

yes,its very tough to diagnose issues with just symptoms and a video but I try my best to guide you guys in the right direction.
its also funny how many things can mimic each other yet be a separate issue.

if that motor has had any care at all since it was new it will run forever,mine is a 95 model and I would not hesitate to take it anywhere.
that said,after you have tuned it to the inth degree and JUST know even looking at the key it will start,,,,,,,,,
and you are a hundred yards off of the rocks in a thirty mph wind,,and it wont even pop,look for your kill switch lanyard on the floor,grandsons can make poppa have a stroke real quick lol.

Yes it is funny that different things will create the same effect. It sounds to me like it is struggling for fuel. Maybe try to run with gas cap cracked open. Could be air leak anywhere and it is real sneaky because it just lets air bubbles in and not fuel out.

One time I had similar and it was just the wire nuts on the battery were not tight enough. It can be many things.

Thanks guys from Iowa and Grouse. Grouse it is a 40 classic, but it’s only got 3 cylinders. I’m going to start with the plugs, then go over the power pack, and coil connections looking for corrosion. This spring I rewired a bunch of electrical, so I’m confident it isn’t a battery connection. I plan on going fishing Friday so I will get to run it then. If it’s still doing it I’ll take the gas cap off and run it awhile. I have no doubt between IDO and the two guys from Iowa, we can get her purring like a kitty. With any luck, the lakes will freeze over again and I can get over this whole boat fishing thing!

My bad grouse you were totally right. 4 cylinders. Heres what the old plugs look like. Look dirty to me. If it means anything to you guys who know about engines……..

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Nothing in here looks corroded. Everything looks like it’s making connection. I may have a small oil leak somewhere. Seems there’s a little oil in the bottom.

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in your spark plug pic i can see two white lines on the bottom right plug that would make me think the ceramic is cracked unless you scratched it like that,cant tell for sure,if it is cracks that will cause a miss.

the plugs also look to be running very rich with a bit of oil fouling,they should be a chocolate brown in color.
I have to ask,what oil are using for it?????

I know I will get flamed for this but it is the absolute truth,if you are running anything but mercury two stroke oil or Lucas in that motor it will never run correctly once you get the misfire straightened out.
I have been doing this a long time and cant be told any different when it comes to oil in mercury engines,been there done that countless times.
I can even prove it with your own motor and a fresh mix of the mercury or Lucas two stroke oil.
why???? mercury oil or Lucas is designed to burn with the fuel charge and its additives will still clean the ports and chambers when it does burn.
yes,mercury knows what they are recommending for oils in their motors and for good reason,it is not a sales pitch period.

there are many good oils out there,dont get me wrong on that but I have seen too many times the other stuff just plain does not cut it,especially in mercs.

as far as corrosion,did you physically take the connections apart and look for the white residue I talked about?? if you did not,take them apart and look.
there are several ground wires on that motor underneath bolt heads that can look great until you take the bolt out and look,this is known problem with them.
as I was once told many years ago,paint hides a lot of sins,corrosion being one of them.

if you cant find anything,time for the shop but I cant help but believe it will be something simple in the end.

in your second picture on the right hand side of the ignition box,there is a black connector,that is the connector to the helm wiring I was talking about pulling apart and checking for corrosion in its pins and sockets,did you check that??

also,the oil you are seeing in the bottom,unless its a huge puddle dont worry about it that is normal,it is blow back from the carbs which is a normal thing that happens with two strokes.

I have discovered on my own this year my carbs are fuel of oil as is the fuel line back to the tank.
there is a brass valve in the oil line from the injection pump that is called a 2psi valve,it is a type of oil pressure regulator as well as a check valve.
when they get weak,they will drain oil from the reservoir into the carbs and fuel line,messy for sure !!
ten bucks later mine will be running like new again.

listened to your video again for the fourth time and an old memory from years ago came flooding back,pardon the pun.
I had a motor come in acting just like yours is,the dang ignition switch was coming apart and grounding out the ignition circuit just like you were turning the switch off and on at a rapid pace.

if you happen to be out on the water and all else fails,ever so gently so you dont engage the starter,wiggle the ignition key just a tiny bit in each direction and see if that makes it quit acting up or makes it worse.

Sheldon, in that plug picture, do you recognize those plugs as being the correct ones?

I don’t ever recall using anything but the standard configuration of plugs.

Grouse

TheFamousGrouse wrote:

Sheldon, in that plug picture, do you recognize those plugs as being the correct ones?

I don’t ever recall using anything but the standard configuration of plugs.

Grouse

They are BUHW-2’s. Sheldon confirmed these are the right plugs to be using via PM.

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TheFamousGrouse wrote:

Sheldon, in that plug picture, do you recognize those plugs as being the correct ones?

I don’t ever recall using anything but the standard configuration of plugs.

Grouse

Grouse,yes,these are the correct plugs for merc motors,that style,( surface gap ) has been used in them for many years,in fact my old 76 twenty horse required them.
the J style you are familiar with can be used,BUT! you have to be careful to get the right ones as the piston in mercs comes so close the plug it can slam the gap shut and or break the plug if the wrong ones are used.

the surface gap plugs are less prone to fouling as well.

Curse motor troubles. Curse them all.

Good luck man, noone deserves bad acting motors.

When I was dealing with mine CDI had a diagnostic one could do with resistance to the power pack. PIA to do but easy and cheap. Also resistance tests on the coils.