Need help--older Mariner 40EL rough idle with bad shaking in gear

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BrounHownd

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So I have a 1982 Merc Mariner 40EL, verified by serial number--it's a tough motor to track down service specs on, as the service manual doesn't really cover the carb or the waste spark ignition system in the specs, along with other topics.

The motor ran and idled when purchased and on the first 2 trips--not well, but hell it's a 40 year old motor. Motor has good compression. Once the weather got warm, took the family out, and after the first run up river and lunch, had a hard start, had to start at throttle then bump immediately into gear to keep it from stalling. Got back fine, put it on muffs in yard and it idled just fine for 20 minutes without issue.

Took it out again fishing, would idle rough and die as soon as I put it in gear. Again, had to bump up the RPMs and engage quickly. Made it back again.

Put in new plugs gapped to Yamaha's spec for their version, matching the old plugs (Mariner manual says "SET" for gap?), pulled the carbs, did a full cleaning and rebuild. Old plugs looked dark, had fuel on them, but I know that's typical for some 2 strokes, but a rich condition bogging it down made sense. One of the float valve tips had almost disintegrated in the carbs, and one of the gaskets was shot. Cleaned, dried, reassembled with new floats, needle valves, and gaskets. Reed valves looked intact when I had the carb bodies off and shined a light in there, but I didn't pull the intake manifold.

Put the motor in a "test tank" (large metal trashcan) and set the carbs 1.5 turns out on the idle mix screw, got them set about 1/4 leaner for "smoothest" idle, but it has to be high to feel somewhat smooth. Has to be much higher than is good for the lower unit at shift to idle at trolling speed smoothly. Took the boat out, and it will now idle, but the engine bucks and shakes the whole boat at trolling idle like it's missing bad. Shaking stops and it smooths out with a bit of throttle (about the time the cam hits the carb pin). Still runs great at speed. Plugs are looking like an over-rich condition if anything, but any leaner on the idle mix screws and it dies. Hard to tell since I idle back into the ramp each time after my run, so they would be a bit oily anyway.

Had it in the test tank again today and the problem persists. Timing looks pretty close based on the static marks and finding TDC through the spark plug hole. Pulled each HT lead with pliers while idling and both cause an immediate stumble--couldn't tell which cylinder was the culprit. Both are kicking spark across 3/8's gap. Haven't put it on the adjustable gap tester yet--need to recruit the wife. Put the multimeter on the coil--this one has the waste spark coil--one input with 2 HT wires coming off, but can't wires be removed. Secondary side is reasonable through the HT leads at 3.5 ohms (it's about 6 inches of HT wire total, maths work out). Primary side is 0.5 ohm input to ground. Yamaha's spec for their version of the motor is 0.8-0.10 ohm on the primary side. Merc's manual says 0.02 to 0.04 on the primary, but I'm not sure it's the same 40hp--they don't cover the waste spark coil system, only 1 coil per cylinder types (referring to a coil tower for the secondary test).

Just wanted to see if anyone in the group thinks I'm off in left field before I spend the money on a NOS coil to try and fix the issue--problem showed up when the weather got warmer and the primary coil resistance being higher than any spec I can find. Next stop is taking the carbs down again and pulling the intake manifold to check the reed valves while I'm in there--I found repalcement gaskets.
 

maintenanceguy

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My guess: idle jets are clogged. I think a complete carb rebuild/cleaning is the solution.

I have the same motor. The ongoing problem with old motors like this is that the plastic and rubber parts are degraded and there will be issues with those parts. Everything else is as good as the day it rolled out of the factory - if it's in good shape. Good compression is a good indicator of good condition.

When I first bought the boat, I did the following:

New fuel hoses from the tank to the carbs. I used 8mm flexible hose from my local race shop.
new fuel filter
new fuel pump
new water separator

Removed, disassembled, cleaned, and reassembled carbs. I had a stuck/broken jet that I couldn't remove without damaging it so I bought a set of used carbs from ebay and between the two sets was able to get a complete, working set.

Removed and inspected the reed valves. These were in good condition and it would be unusual for them not to be.

Set the timing according to the factory service manual.

I also bought and added a 5hp kicker motor as a backup to let me putt-putt back to the ramp if everything I did above ever lets me down.

Everything has been good.

Here's the service manuals.
Mariner_Manual_Design_Fundamentals.pdf
Mariner_40hp_manual.pdf
 

nccatfisher

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You really need to set your carbs to run best on the water, not in a trashcan.
 

BrounHownd

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maintenanceguy said:
My guess: idle jets are clogged. I think a complete carb rebuild/cleaning is the solution.

I have the same motor. The ongoing problem with old motors like this is that the plastic and rubber parts are degraded and there will be issues with those parts. Everything else is as good as the day it rolled out of the factory - if it's in good shape. Good compression is a good indicator of good condition.

When I first bought the boat, I did the following:

New fuel hoses from the tank to the carbs. I used 8mm flexible hose from my local race shop.
new fuel filter
new fuel pump
new water separator

Removed, disassembled, cleaned, and reassembled carbs. I had a stuck/broken jet that I couldn't remove without damaging it so I bought a set of used carbs from ebay and between the two sets was able to get a complete, working set.

Removed and inspected the reed valves. These were in good condition and it would be unusual for them not to be.

Set the timing according to the factory service manual.

I also bought and added a 5hp kicker motor as a backup to let me putt-putt back to the ramp if everything I did above ever lets me down.

Everything has been good.

Here's the service manuals.
Mariner_Manual_Design_Fundamentals.pdf
Mariner_40hp_manual.pdf

Such great information, thanks! Those manuals are worth their weight in gold, I will put them to good use.

My only question would be--if it's a clogged idle circuit, why would the cylinders look overly rich? Wouldn't an obstructed circuit starve the engine of fuel and present as a lean condition?

Going to double check the timing and go through the carbs again.

Thanks.
 

BrounHownd

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nccatfisher said:
You really need to set your carbs to run best on the water, not in a trashcan.

I would argue that a trashcan filled close to the water line would be pretty dang close to being "on the water" from the perspective of idling, my friend. Only the low-speed circuit is adjustable on this motor--and high speed works fine. That trash can looks a lot like a "test tank" that the pros use to work on them/ :wink:

Backpressure is backpressure on the exhaust. Regardless, it would allow one to get a heck of a lot closer than on muffs--close enough that you wouldn't expect the engine to be bucking and missing.

But I appreciate you reading and providing some feedback.
 

BrounHownd

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As an update, went through the timing and throttle linkage setup per the manual. Timing was close, but not quite there. Linkages were micky-moused and pretty far off. Thinking previous owner or his cut rate "tech" tried to adjust away a deeper issue.

Also pulled the coils and CDI and put a meter to them. Coil primary is reading about 4x spec resistance, and all CDI resistances measured from the trigger wire (white red striped) with the red lead we're 2-3x the high end of spec. All others were good.

If the CDI isn't triggering at the right time that could cause some spark strength and timing issues as well, I'd imagine.

Gonna see of those parts resolve the issue and if not rebuild the carbs again. If nothing else, I'll have a spare coil and CDI in the toolbox.
 

nccatfisher

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BrounHownd said:
nccatfisher said:
You really need to set your carbs to run best on the water, not in a trashcan.

I would argue that a trashcan filled close to the water line would be pretty dang close to being "on the water" from the perspective of idling, my friend. Only the low-speed circuit is adjustable on this motor--and high speed works fine. That trash can looks a lot like a "test tank" that the pros use to work on them/ :wink:

Backpressure is backpressure on the exhaust. Regardless, it would allow one to get a heck of a lot closer than on muffs--close enough that you wouldn't expect the engine to be bucking and missing.

But I appreciate you reading and providing some feedback.
How are you keeping that trashcan full of water full up to the normal water line like it would be in a normal operating situation? Especially when it is bucking and spitting? Any time I have seen someone trying to do do that they wind up with the water blown out all over the place and poorly adjusted engine.
 

BrounHownd

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nccatfisher said:
BrounHownd said:
nccatfisher said:
You really need to set your carbs to run best on the water, not in a trashcan.

I would argue that a trashcan filled close to the water line would be pretty dang close to being "on the water" from the perspective of idling, my friend. Only the low-speed circuit is adjustable on this motor--and high speed works fine. That trash can looks a lot like a "test tank" that the pros use to work on them/ :wink:

Backpressure is backpressure on the exhaust. Regardless, it would allow one to get a heck of a lot closer than on muffs--close enough that you wouldn't expect the engine to be bucking and missing.

But I appreciate you reading and providing some feedback.
How are you keeping that trashcan full of water full up to the normal water line like it would be in a normal operating situation? Especially when it is bucking and spitting? Any time I have seen someone trying to do do that they wind up with the water blown out all over the place and poorly adjusted engine.

I use a hose clamped to the side, sorta like I imagine most folks would in a similar situation.

In any measure, I don't think a few inches of water would mean the difference between a bucking motor and a butter smooth idle.

I promise when I get it close I'll take and tie it to the dock for final adjustment. Just for you. :wink:
 

RaisedByWolves

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Interesting that you ask for help and are getting very good advise, but are acting like an ***.

I had typed out a detailed synopsis of where your thinking is wrong and what points you are missing, but the either ate and I’m not going to retype it all... just for you.

Enjoy throwing your money away chasing parts.
 

BrounHownd

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RaisedByWolves said:
Interesting that you ask for help and are getting very good advise, but are acting like an ***.

I had typed out a detailed synopsis of where your thinking is wrong and what points you are missing, but the either ate and I’m not going to retype it all... just for you.

Enjoy throwing your money away chasing parts.

I think you'll note I've been very appreciative of the solid advice I've received this far, and only a bit prickly to those that came in hot on assumptions and preconceived notions.

That said, your snideness isn't exactly welcomed either. If you want to join the discussion, jump in and I'll be greatful if it's valid, well considered, and thoughtfully related to the actual issue. A trash can isn't causing my problem, as noted by the issue showing up on the river itself. If you'd rather be snarky and have thrown away that time for nothing, that's up to you.

Finally, at this point it's not really "my" thinking, it's the service manual specs. If going by those is misguided, I'm very curious to hear your thoughts.
 

RaisedByWolves

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BrounHownd said:
RaisedByWolves said:
Interesting that you ask for help and are getting very good advise, but are acting like an ***.

I had typed out a detailed synopsis of where your thinking is wrong and what points you are missing, but the either ate and I’m not going to retype it all... just for you.

Enjoy throwing your money away chasing parts.

I think you'll note I've been very appreciative of the solid advice I've received this far, and only a bit prickly to those that came in hot on assumptions and preconceived notions.

That said, your snideness isn't exactly welcomed either. If you want to join the discussion, jump in and I'll be greatful if it's valid, well considered, and thoughtfully related to the actual issue. A trash can isn't causing my problem, as noted by the issue showing up on the river itself. If you'd rather be snarky and have thrown away that time for nothing, that's up to you.

Finally, at this point it's not really "my" thinking, it's the service manual specs. If going by those is misguided, I'm very curious to hear your thoughts.

You get what you give.

I mean if you’re so smart, fixing this should be a breeze, right?

Enjoy!
 

BrounHownd

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RaisedByWolves said:
BrounHownd said:
RaisedByWolves said:
Interesting that you ask for help and are getting very good advise, but are acting like an ***.

I had typed out a detailed synopsis of where your thinking is wrong and what points you are missing, but the either ate and I’m not going to retype it all... just for you.

Enjoy throwing your money away chasing parts.

I think you'll note I've been very appreciative of the solid advice I've received this far, and only a bit prickly to those that came in hot on assumptions and preconceived notions.

That said, your snideness isn't exactly welcomed either. If you want to join the discussion, jump in and I'll be greatful if it's valid, well considered, and thoughtfully related to the actual issue. A trash can isn't causing my problem, as noted by the issue showing up on the river itself. If you'd rather be snarky and have thrown away that time for nothing, that's up to you.

Finally, at this point it's not really "my" thinking, it's the service manual specs. If going by those is misguided, I'm very curious to hear your thoughts.

You get what you give.

I mean if you’re so smart, fixing this should be a breeze, right?

Enjoy!

If I didn't want input, I wouldn't have asked. But if you're really that mad about me giving as good as I got about the trash can sideshow, it's probably time to move along. Besides, that advice was about the last 2% of this process.... we're a long way from there.

If not, I welcome your ideas.
 

maintenanceguy

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I have a 55 gallon plastic drum that I've cut down to about 40 gallons. I test, tune, and repair my outboards in that and it has always worked fine for me. Maybe there's something different about testing it on the water but it's sure inconvenient when all my tools and my shop are on dry land.

Trailering to the nearest ramp, looking for a place to dock out of everyone's way, working without all of my tools available, and trying to make repairs hanging off the back of the boat seems like the hard way to do it.
 

BrounHownd

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maintenanceguy said:
I have a 55 gallon plastic drum that I've cut down to about 40 gallons. I test, tune, and repair my outboards in that and it has always worked fine for me. Maybe there's something different about testing it on the water but it's sure inconvenient when all my tools and my shop are on dry land.

Trailering to the nearest ramp, looking for a place to dock out of everyone's way, working without all of my tools available, and trying to make repairs hanging off the back of the boat seems like the hard way to do it.

Completely agree.

The one downside to tuning at home, though, is the beer cans are still in the yard the next morning after you throw them overboard.



KIDDING.
 

RaisedByWolves

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BrounHownd said:
RaisedByWolves said:
Interesting that you ask for help and are getting very good advise, but are acting like an ***.

I had typed out a detailed synopsis of where your thinking is wrong and what points you are missing, but the either ate and I’m not going to retype it all... just for you.

Enjoy throwing your money away chasing parts.

I think you'll note I've been very appreciative of the solid advice I've received this far, and only a bit prickly to those that came in hot on assumptions and preconceived notions.

That said, your snideness isn't exactly welcomed either. If you want to join the discussion, jump in and I'll be greatful if it's valid, well considered, and thoughtfully related to the actual issue. A trash can isn't causing my problem, as noted by the issue showing up on the river itself. If you'd rather be snarky and have thrown away that time for nothing, that's up to you.

Finally, at this point it's not really "my" thinking, it's the service manual specs. If going by those is misguided, I'm very curious to hear your thoughts.

What preconceived notions led you to post

"That trash can looks a lot like a "test tank" that the pros use to work on them/ :wink:"

And

"Just for you"

To Nc cat?

Because his advise was spot on and you weren't "Far from there", though now that you have gone deeper into the motor than you should have you might just be further from fixing it.

Are you a pro setting up a motor with all the right tools they have at their disposal? AKA, the test tank?

Did you think the "just for you" was a witty reply to someone who was out of their league?

I mean, you did start off snapping carb jets off in your pursuit to "Fix" this motor, so what are we supposed to see of you in all of this given the above Snarky reply's?

You want help here, youll get help.

Normally there are 4-5 people chiming in with advise just like NC's reply, but there arent, why is that?
 

BrounHownd

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Advice just like NC Cat?

You mean that my whole issue is because I'm using a trash can? That I clearly stated it was doing the exact same thing on the water BEFORE the trash can ever came into the picture? I appreciate the thought, but I really don't see the connection--it came across as someone that doesn't have an answer but has to say something anyway. Sorry I responded in kind.

Advice like the left field stuff you've offered in some of your posts in the past?

I'll pass, friend. You're welcome to move along.
 

MrGiggles

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Running in a barrel will get you close, however, most service information recommends setting the idle jets in gear, at idle speed. In my experience, putting the outboard in gear in a barrel results in an empty barrel and wet pants.

Get it close in the barrel and fine tune with the motor idling in circles on the lake. There are usually rubber plugs that you can pop out of the air box to access the screws, without removing anything but the cowl.

The thing you shouldn't do is set them on muffs, your settings will be way off without the back pressure from the exhaust being submerged.

Give the adjustable gap tester a try, make sure it will jump a pretty large gap, around 3/8-1/2" is pretty acceptable.

Resistance testing is largely useless, you need a DVA to properly load the components and get an accurate measure of their performance, but that is really only necessary if you have found a weak/no spark condition.

I think you are on the right track of going through the link and sync procedure, as well as getting the idle jets set properly. I would also do a quick compression test as well, just to ensure you aren't chasing your tail.

Additionally, you can pull the plug wires one at a time with a well insulated pair of pliers to narrow down which cylinder is misfiring.
 

BrounHownd

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MrGiggles said:
Running in a barrel will get you close, however, most service information recommends setting the idle jets in gear, at idle speed. In my experience, putting the outboard in gear in a barrel results in an empty barrel and wet pants.

Get it close in the barrel and fine tune with the motor idling in circles on the lake. There are usually rubber plugs that you can pop out of the air box to access the screws, without removing anything but the cowl.

The thing you shouldn't do is set them on muffs, your settings will be way off without the back pressure from the exhaust being submerged.

As for your issue, if you are getting a good, fat spark like you say, there is no point in going any further with ignition system testing.

Resistance testing is largely useless, you need a DVA to properly load the components and get an accurate measure of their performance, but that is really only necessary if you have found a weak/no spark condition.

I think you are on the right track of going through the link and sync procedure, as well as getting the idle jets set properly. I would also do a quick compression test as well, just to ensure you aren't chasing your tail.

Good stuff. Thank you. Luckily my setup stays pretty full when I put it in gear, but I see how it could be an issue. I just need to get it to a point it's not shaking my fillings out before I clock out on a weekday and drive all the way to the nearest quiet ramp with a dock.

Haven't had time to hook everything back up since I put a meter to the ignition system, but I'll keep you posted. Having that manual specific to the motor has been a huge help. Plan to see if the timing adjustment and linkage reset help. Carbs were synced when I put them back on....they open at exactly the same time and move together with the idle screw.

As to spark, best I can see is that there is spark there...it's a side console and I don't have a remote switch. Can't tell the quality. But have a timing light I borrowed I can use to look for misses once I reconnect it all if the other work doesn't improve things.
 

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BrounHownd said:
MrGiggles said:
Running in a barrel will get you close, however, most service information recommends setting the idle jets in gear, at idle speed. In my experience, putting the outboard in gear in a barrel results in an empty barrel and wet pants.

Get it close in the barrel and fine tune with the motor idling in circles on the lake. There are usually rubber plugs that you can pop out of the air box to access the screws, without removing anything but the cowl.

The thing you shouldn't do is set them on muffs, your settings will be way off without the back pressure from the exhaust being submerged.

As for your issue, if you are getting a good, fat spark like you say, there is no point in going any further with ignition system testing.

Resistance testing is largely useless, you need a DVA to properly load the components and get an accurate measure of their performance, but that is really only necessary if you have found a weak/no spark condition.

I think you are on the right track of going through the link and sync procedure, as well as getting the idle jets set properly. I would also do a quick compression test as well, just to ensure you aren't chasing your tail.

Good stuff. Thank you. Luckily my setup stays pretty full when I put it in gear, but I see how it could be an issue. I just need to get it to a point it's not shaking my fillings out before I clock out on a weekday and drive all the way to the nearest quiet ramp with a dock.

Haven't had time to hook everything back up since I put a meter to the ignition system, but I'll keep you posted. Having that manual specific to the motor has been a huge help. Plan to see if the timing adjustment and linkage reset help. Carbs were synced when I put them back on....they open at exactly the same time and move together with the idle screw.

As to spark, best I can see is that there is spark there...it's a side console and I don't have a remote switch. Can't tell the quality. But have a timing light I borrowed I can use to look for misses once I reconnect it all if the other work doesn't improve things.

Leave the ignition key on, and rig up a short jumper wire on the starter solenoid, which is conveniently located under the cowl, to crank without using the ignition.

An adjustable gap tester is needed to measure ignition performance. Just having spark at the plug is not enough, since the resistance of air goes up when it is compressed and heated, could have good spark out of the cylinder and nothing under compression.
 

BrounHownd

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MrGiggles said:
Leave the ignition key on, and rig up a short jumper wire on the starter solenoid, which is conveniently located under the cowl, to crank without using the ignition.

An adjustable gap tester is needed to measure ignition performance. Just having spark at the plug is not enough, since the resistance of air goes up when it is compressed and heated, could have good spark out of the cylinder and nothing under compression.

Great idea--not sure why it didn't occur to me to do that.
 
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