Merc 15 hp is getting the best of me, I'm at a loss, won't run right (S/N 0T533347)

First, thanks to everyone that has helped me so far, as I've posted a couple of times as I worked my way through trying to get a 2002 Mercury 15hp short shaft 2 stoke outboard to run right. It still won't though. It seems to load up (rich) and then cough a big puff out of the exhaust, then drop off. Let it run long enough, and the idle will slow down and it will stall. Give it gas, and it will bog, or pop/cough like in this video.

https://www.dropbox.com/s/ebr8hexck07q36s/IMG_0875.MOV?dl=0

Here's some info on it...it will start pretty easily. When it dies, it can be really hard to restart. Usually you need to turn the primer knob to FAST and it will catch. It's was like this last season too. Once running, it will run for a while, and then slow down or if you get into the gas, it pops like I mentioned. Last season, we did use it and it was ok for the most part, but always fussy with hard starts and restarts and stalls sometimes.

I'm pretty handy and have checked quite a bit. Here's the list of what I've looked at and done...

1. Carb cleaned (no improvement), but I'm even doing it again in the ultrasonic cleaner (as I write this).
2. Confirmed plug wires were bad. Intermittent connections. New wires installed.
3. New thermostat (although that had nothing to do with any of this, it just needed it).
4. New fuel filter and O ring.
5. Checked reed block, reeds all look great.
6. New plugs, and confirmed good spark using an adjustable gap tester. Spark jumped a 1/2" gap with a nice blue spark. Same for both cylinders. Also confirmed proper gap of 0.060"
7. Confirmed the ignition coils ohmed out correctly.
8. Found the kill switch in the tiller handle was bad (removed that). New one arriving tomorrow.
9. Verified the safety lanyward kill switch ohms out correctly (open, or .5 ohm when activated).
10. New fuel and the proper mix, 50:1.
11. Adjusted carb float, as it was way out of spec. It was only at about 1/4" from bottom of bowl, vs the 1" the service manual stated. I adjusted the lever in the bowl to allow it to rise to the proper level.
12. Checked compression and while low, both cans were 105psi dead on.

And the darn thing still won't run right! A few things I've noticed...so here's the questions, in addition to any other advice anyone might have.

1. Look at the plugs in the pics below. One was fouled, the other looked like it was very lean. Why such a difference?

2. And then on the reed block, at the bottom left there's two small holes that look like they allow the crankcase to bleed through the reed block, back into the carb into the overflow hose under the carb. It's circled in the pic. I noticed there's like a small piece of plastic in there that blocks the passage a bit. Seems like it moves around. Is it some type of check valve? Or should those holes both be clear and I should try to get it out. Seems like in most cases, only one holes is blocked at a time, but I could be wrong.

3. On the carb bowl, I'm curious about the bowl and two things related the primer circuits. Both areas are circled in the pic. First, the brass insert at the bottom of the bowl. It seems like there's a small brass flapper valve or something. Could that be damaged and somehow causing a problem? And the hole at the top of the bowl that is circled. Is that a tube going somewhere? It's seems blocked so it's either clogged or not a circuit. Why the hole then? Hoping the ultrasonic cleaner opens it up if it is supposed to pass fuel.

I'm handy with tools, and like to learn. Not afraid to do too much, but I'm thinking it's something stupid. The three things to have an engine run, spark, fuel and air. I think I have them all.

You may have more than 1 problem.
To answer your question #3, I have had that little check valve in the side of the float bowl fail on me.
It allows fuel to come from the float bowl into the primer bowl. When you prime, it blocks fuel from
coming out of the primer bowl back into the float bowl. The little hole you have circled is a passage
for air to exit the primer bowl as it fills. That air is vented back into the float bowl.
Good luck! Keep at it...

It's only running on 1 cylinder. From What I heard on the video . You say it has good spark using a spark gap tester. Did you confirm also the spark at the spark plugs?
One clean plug and one sooty plug. Was the clean plug wet when you took it out?

Thank you both for the replies...

First whitegreg56, so if that little passage should allow air to exit the primer bowl as it fills, I assume that means I should easily be able to feel air pass through that circuit then. I am running the bowl through the ultrasonic cleaner again. When I blew it out after with compressor, I did get some bubbles out of the hole at the top of the primer bowl, but it''s not clear, that is clear! Keep trying?

mechanicman, thank you. I thought it might be on one cylinder as well. The clean plug was pretty dry, just a very faint hint of tan on one part of the flat surface, but otherwise, it looked like a new plug. Can you elaborate on your question about confirming spark at the spark plug? I also have an inline spark plug tester as well. I will do that now.

Also, it looks like something is seriously off on your float level.
Changing from 1/4 inch to 1 inch is a huge change.
When you are measuring, do you have the carb upside down?
And, you are not putting pressure on the float...just gravity.
Is the needle present and seating properly?

If you spray some WD-40 or carb cleaner into the little hole at the top of the primer bowl,
something should definitely come out of the little hole you circled...if it doesn't, you have
a problem.

Confirming spark: using the spark plug to test for spark. To see color . What color is the spark?

I agree that one cylinder is probably not getting spark...you say you replaced
the plug wires. Did you check that the new ones are OK? From inside the spark plug boot,
through the ignition coil to ground?

whitegreg56 said:

Also, it looks like something is seriously off on your float level.
Changing from 1/4 inch to 1 inch is a huge change.
When you are measuring, do you have the carb upside down?
And, you are not putting pressure on the float...just gravity.
Is the needle present and seating properly?

Click to expand...

Yes, upside down, just using gravity. Needle is in there and as far as I can tell, yes, it's seated fine, and a close up pic of the tip shows no damage. I made a gauge to measure. Here's a pic. The top of the black mark at the left is 1" from the underside of the top part of the bracket that rests on the carb throat. That's 1". Unless I misunderstood the service manual. It was only about 1/4" down before.

mechanicman said:

Confirming spark: using the spark plug to test for spark. To see color . What color is the spark?

Click to expand...

I did that earlier, yes, against the motor. I'd saying bluish white was the color for both, with an equal strength. I also just tried the inline tester, which is much harder to do with a manual start engine as you are pulling but you don't want it to start. The light in the tester lit but was weak. I'm not sure how strong it should be, but I wasn't impressed with what I saw.

I was thinking of starting it tomorrow, and pulling one wire at a time and seeing if it dies and which one. The top cylinder was the clean dry plug, and the bottom was the wet fouled one. Could timing have anything to do with this? I really don't think so, but thought I'd throw it out there. I have not confirmed the timing of 8 degreed btdc +/- 1 degree.

And whitegreg, second time through the ultrasonic cleaner and more bubbles, seemed like progress. Running it again while heating the cleaning solution...At least I know there what I'm after. As for testing the new spark plug wires, I didn't test through the coils and wires to ground. I just did a continuity/resistance test to confirm a good wire. Should I try what you mentioned?

Also, all parts I get are Mercury OEM, I don't buy much aftermarket.

Many times there is a bad connection between the ignition coil and the spark plug wire.
Is the inside of the cavity on the ignition coil clean? Measure the resistance from inside
the spark plug boot to a clean engine ground (keep your fingers off the measurement probes).
What resistance do you get? I believe the resistance listed in my manual is off by a factor of 10.
May be able to confirm that for you later (I have the same engine....except 8 HP).

It is possible you have a bad "switch box". But, that is an expensive component!

I think the manual is off by a factor of 10 for coil resistance too. It says the ohms for the coil should be .02-.04 and I believe it should be .2-.4. At least that's what I got for a reading on my meters lowest scale (up to 0-400 ohms).

Anyway, the coils look clean inside where the wire goes. Measuring from the inside of the spark plug end of the wire, in the boot, to ground, I get no reading (OL). That makes sense right, because the plug wire is positive, so you shouldn't have a connection to ground, as that would be a short? I don't recall seeing a reading for that in the service manual.

Also, on that carb bowl, I tried to get that little air circuit clean 4 times through my ultrasonic cleaner with no real success. Assuming it should be easy to tell air is moving, I've failed. It's clogged pretty good. Should I pick up a new bowl? It's about $50, so don't want to unless I need to. But if I need it, no problem. Just not sure how much air should obviously be flowing.

Curious too what you think of my explanation of my float bowl adjustment and measurement. Sound like I did it right? Pretty sure I did.

Thanks so much for the help so far!

The coil primary is probably fine.
It is the coil secondary that needs to be checked. If you measure from
the inside of the spark plug boot to ground, you should NOT get infinite
resistance (OL). It should be the resistance of the coil secondary.... I believe 800~1100 ohms.
We may have located your problem.

Get a spray can of carb cleaner (with a straw) and put it right in the primer bowl hole and spray.

Float bowl looks OK. Not sure how you got the measurement if it was only 1/4 inch down.
But, that's irrelevant at this point.

On the float bowl, just for clarity, when I first measured it, the bottom of the bowl was about 3/4" from top of the throat as measured in the picture. It was off by a 1/4". So I adjusted the lever to allow it to (raise technically, but it's upside down for measuring) drop an additional 1/4" so the bottom of bowl was 1" below the top oft the throat.

On the coils, I think I know what I did wrong. I had the meter most likely on the lowest scale, which only goes to 400 ohms, so being over at 800-1000, it would be a true OL. I will check this again on the right scale. Stupid mistake on my part (I know better), but it was a long day with this motor. LOL. I thought it seemed odd, but then convinced myself it made sense! More later on when I'm home.

Thanks for sticking with me!

Small resistances are difficult to measure....if the meter shows continuity, it's probably OK.

In the Service Manual, under specifications, ignition system, the ignition coil secondary, shows 8000~11000 ohms.
I believe this is wrong....should be 800~1100 ohms. The secondary is made with a very fine wire....it is a
frequent source of failure. So make a measurement from the boot to engine ground.....on both of them.

I just measured it. I got 913 ohms on one coil, and 921 ohms on the other. And everything I read says you are correct, not 8000-10000. So they seem good. Ugh.

On that bowl too I tried carb cleaner, compressed air, and 4 runs through the ultrasonic cleaner. Nothing opened that air circuit up anything meaningful. I put some paper towel next to the opening in the primer bowl and blew about 50psi through from the carb bowl, and the paper towel didn't even move.

I'm planning on firing it up soon, and seeing if I pull the wire, one at a time, what happens...

Ok, just came in. It's definitely running on both. I pulled each wire, one at a time, and it died each time I pulled one. But as you will see, once it died the second time, I had a hard time getting it restarted. I had idle too low. Got it restarted after, and then it ran for about two minutes then slowly lost speed and died, and then I had a hard time getting it going again. Here's the video of the plugs being pulled:

https://www.dropbox.com/s/2iqymnmlizoxtjj/Plug pull test.MOV?dl=0

Bad fuel pump diaphragm, so losing fuel? That plugged circuit in the carb causing some type of vapor lock? Perhaps even though I thought the carb was super squeaky clean that perhaps the idle circuit still has junk in it (REALLY unlikely, except for that one spot we are talking about, every circuit blew out clean).

2 minutes....you may be running out of fuel. Possible bad fuel pump....runs off the pressure variation in the crankcase.
Try squeezing the primer bulb on the fuel line every now and then.
See if that keeps it running.

Also, set the low-speed mixture screw (above the intake) according to the service manual.

Right now the low speed mix screw is per manual, 1.5 turns out. I'm going out now to try compressing the bulb myself, to act as a fuel pump. I thought this was an issue before, but then it seemed to not be. Maybe this is.

I will say, when it was running, and I had the inline spark tester installed, it was a very dim light. Not sure how bright it should be on a small motor at idle...

Well this was interesting...I just ran it, and I got tired of waiting for it to die, so I shut it off. Probably ran for 8-10 min. In gear, no coughing or puffing. Idle seemed stable, although high idle wasn't quite in spec (1300). I did pump the bulb a few times. Probably shouldn't have. I'll go back out in a few and try again, and I won't touch the bulb once it's running.

Here's a couple of videos...

https://www.dropbox.com/s/3cgg0o1idrc8ef2/running1.MOV?dl=0
https://www.dropbox.com/s/d8cgm1390gfp2k3/running2.MOV?dl=0

I've never touched the fuel pump, but had it apart each time I cleaned the carb. I should probably just replace the diaphragm anyway, although it seems like you can't buy it separate, only as part of the carb kit. I need to look more at that.

And then I need to decide if I should replace the bowl since nothing seems to want to open up that little air passage. Also, given what I'm showing of my float, do you believe I did that right? Maybe I should get a new float needle too.

I bought the motor last year, so getting back to a baseline isn't a bad thing.

As I need this outboard to be stable, since my kids use this dinghy in a river with 5-6 knot current at times, I went ahead and ordered some of the stuff to make sure parts of unknown condition are replaced. I ordered the fuel pump diaphragm and gasket, new carb bowl needle, and a new fuel bowl. I also will replace both small fuel lines as they look old and have some cracking. Perhaps some air is getting sucked in. I will get this sorted out...

The real spark test.-------Does spark jump a gap of 3/8" on both leads , yes or no ?

Yup I mentioned that above. I was probably almost 1/2”, but certainly at least 7/16”, and it jumped no problem.

Quick update. New parts came today. The carb bowl is much better. That hole/circuit we've been discussing is easy to blow are through on the new bowl, so I'm sure that was causing me grief with the old bowl since it was clogged. Then I noticed my old needle was a bit deformed at the end, like it was scored. Perhaps that was leading to some flooding. Who knows. But then the diaphragm was a mess compared to the new one. I think it had little compression and ability to pump. Then there's the EPA automatic vent caps on the portable tanks. Couple that 5psi requirement with a weak fuel pump and bad things will happen. All new parts are installed, but it's late. I was working on the big boat most of the day, so didn't get to this till tonight. I'll fire up the outboard in the morning and see what happens. Not sure what else there is to fix/check!

Boy am I discouraged. This little motor is proving to be a stubborn one...With the new fuel pump diaphragm, bowl needle ,and fuel bowl, it is starting much easier now. MUCH. So no regrets there.

But it is still fouling plugs and coughing through the exhaust. And if you let it sit, it will slowly die off and stall. BUT, if I start pumping the fuel bulb, I can prevent the stall and it catches up. So could this all be a fuel delivery issue, or still a combo of things? I figure the fuel pump is good now (the pump itself looked perfect, but is NLA anyway), and the gasket is new too. So can't imagine there's an air leak unless it's somewhere else.

I do notice if I shut it down, the bulb doesn't stay hard, and I'm talking about even if you try to restart within a couple of minutes of shutting it down. You have to repump to build it up to restart. Should I get a new bulb and see what that does? Any way to test one? No signs of cracks or anything, but who knows. And to make sure the fuel tank isn't starving it, I have an old school non EPA vented cap on the tank too.

Open to any new ideas.

To make matters worse, in my frustration, I restarted the darn thing but forgot to turn the water on. It ran about 10-15 seconds at idle before I realized my stupidity before I shut it down. Pump seems fine when I restarted, it was pumping fine and the water pump likely still was pretty wet inside as it just ran a few minutes before with water of course.

Just tried a new bulb and fuel line. No improvement. I’m convinced it’s an air leak under the coal somewhere.

Sounds like you have got the primer straightened out.

With new plugs, do they look different after running for a while?

If the bulb is going totally soft, there may be an air leak. Is the fuel strainer bowl threaded on correctly with an O-ring?

Also, the idle mixture adjustment cannot just be set on a starting point. It has to be adjusted with testing according to
the service manual. You will need to make very small adjustments ( 1/8 of a turn ) and wait for things to stabilize after
each adjustment....give it 20~30 seconds. This setting may be why you are slowing down and eventually stalling out.

Plugs look more consistent. And yes the fuel filter bowl is on straight and has a new o ring. No visible signs of fuel leaks anywhere. The bulb doesn’t get super soft like flat, but if I pump on it the motor stays running but struggles. Here’s a datapoint. When running at high idle it revs that starts dropping off pretty quickly.

On the idle idle adjustment I am starting over the service manual at 1.5 turns out from lightly seated. But I may be adjusting too much with 1/2 turns. I’ll go slower and see if that helps. What’s the best way to track down a possible air leak? It really feels like fuel starvation. At least one of the issues does.

The more I read, the more I'm wondering if my coughing/backfire through the exhaust is a lean condition that's worsened by the fact that the outboard is running on muffs and not in water with proper backpressure. I've read about the differing results you can get when running an outboard with no load. I think before I go too crazy, I'm going to get it in a bucket of water and run it that way and see what I get. I'm not sure if this solves the stalling after a while, but we will see...

I'm curious about a gasket that should exist between the reed block (part 828435A3) and the cylinder block. Looking at the parts diagram, one is not shown, but is it considered part of the reed block assembly and not sold separately? When I pulled my reed block, there was just a factory recessed rubber ring around the reed block, but no paper/fiber gasket like the one between the carb and reed block. Should there be one, could I be sucking in extra air from there?