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Mercury outboard

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unclaimed baggage
1st Mate

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USA
45 Posts

Initially Posted - 09/06/2010 : 15:24:21

It has been idling rough and tought to start lately. Yesterday after blowing out the main sheet, I would keep cutting out motoring back to the slip.

Do I just need to run it wide open to burn off carbs?

Water in fuel?

what do ya think?

Eric F Martinez
1985 Fix keel, Tall rig

Edited by - on

jerlim
Master Marine Consultant

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USA
1484 Posts

Response Posted - 09/06/2010 : 16:14:53

Eric - you didn't say how old the motor is, or w/ how many hours of use...but our 2006 Merc 8hp, 4 stroke, with about 250 hours had similar issues, and finally would not start - which required our sailing back into the marina under head sail alone...the problem turned out to be ethanol related...check the 'fuel additives survey' thread in the General Forum for more details - but the short of it was salt deposits in the carb (from water in the gas) and gunk from a breakdown of the lining of the fuel line and the diaphragm of the pump - resulting in a costly repair...

Edited by - on

Tom Gauntt
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204 Posts

Response Posted - 09/07/2010 : 05:54:19

Eric,

Is it a two-stroke or a four-stroke? If it's a 2-stroke, you might wish to start with checking/replacing the spark plugs. Two-strokes are notorious for fouling the plugs, especially if they're run at low-RPM for long periods of time.

Edited by - on

Stuff4Toys
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83 Posts

Response Posted - 09/07/2010 : 07:37:58

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by jerlim
 Eric - you didn't say how old the motor is, or w/ how many hours of use...but our 2006 Merc 8hp, 4 stroke, with about 250 hours had similar issues, and finally would not start - which required our sailing back into the marina under head sail alone...the problem turned out to be ethanol related...check the 'fuel additives survey' thread in the General Forum for more details - but the short of it was salt deposits in the carb (from water in the gas) and gunk from a breakdown of the lining of the fuel line and the diaphragm of the pump - resulting in a costly repair...
<hr height="1" noshade id="quote"></blockquote id="quote">Your problem was actually bacteria growing in the ethanol (like little barnacles) and corroding your aluminum carb. Make sure you add an enzyme treatment to your gasoline. The same stuff they use for diesel will work fine for ethanol.
JOhn ><>

Edited by - on

Stuff4Toys
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83 Posts

Response Posted - 09/07/2010 : 07:41:28

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by unclaimed baggage
 It has been idling rough and tought to start lately. Yesterday after blowing out the main sheet, I would keep cutting out motoring back to the slip.
Do I just need to run it wide open to burn off carbs?
Water in fuel?
what do ya think?
<hr height="1" noshade id="quote"></blockquote id="quote">
All of the above. Gasoline should not be stored for more than a month or two WITH treatments like stabil, a little longer with others. Put a sample of your gas in a clear jar and let it set still for 10-15 minutes. If you see anything settle out, you have either water or phase separation.
Toss the gas and replace.
You may also need to have the carb done at this point and always a good opportunity to change spark plugs.

Edited by - on

unclaimed baggage
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45 Posts

Response Posted - 09/07/2010 : 13:10:21

It is a 2005 I try to constantly keep the fuel tank full to prevent condensation in the fuel. I have put Stabil in it previuosly just not in the last 1/3 of a tank I topped it off with.

I have no idea how many hours are on it. I would guess very few.

Edited by - on

Stuff4Toys
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83 Posts

Response Posted - 09/07/2010 : 13:38:59

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by unclaimed baggage
 It is a 2005 I try to constantly keep the fuel tank full to prevent condensation in the fuel. I have put Stabil in it previously just not in the last 1/3 of a tank I topped it off with.

I have no idea how many hours are on it. I would guess very few.
<hr height="1" noshade id="quote"></blockquote id="quote">How old is the gas?
Take a sample in a glass jar and see if it separates.
If all is OK then check/change the plugs.
Wide open will do little or nothing to help the carbs, Might burn the carbon off the plugs, but if you change them, no matter.

Again Check the Gas!!!
JOhn ><>

Edited by - on

cks
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126 Posts

Response Posted - 09/07/2010 : 16:42:45

my suggestion is to try adjusting the idle screw and see if you can get the motor running more smoothly. if you do as you're supposed to and adjust the screw down until it almost stalls and turn it a quarter turn the other way, my outboard still runs a little rough (although it doesn't stall). Last season, I just turned the idle screw until the rough idling stopped(although you'll noticed increased rpm's and higher noise).

Edited by - on

Stuff4Toys
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83 Posts

Response Posted - 09/07/2010 : 17:00:28

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by cks
 my suggestion is to try adjusting the idle screw and see if you can get the motor running more smoothly. if you do as you're supposed to and adjust the screw down until it almost stalls and turn it a quarter turn the other way, my outboard still runs a little rough (although it doesn't stall). Last season, I just turned the idle screw until the rough idling stopped(although you'll noticed increased rpm's and higher noise).
<hr height="1" noshade id="quote"></blockquote id="quote">IMHO Don't Mess with the screws!!!!! It was fine before the problem started, and it WILL NOT help!!! IMHO
I don't want to make any enemies on this forum, but I've been running a marine dealership for 10 years. Changing the idle mixture will not effect the way the engine runs at half throttle, ONY AT IDLE!

JOhn ><>

Edited by - on

Dave5041
Former Mainsheet Editor

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3758 Posts

Response Posted - 09/07/2010 : 17:33:30

I have to agree with Stuff4Toys. Idle mixture is just that. Adjusting with the near stall technique is for a healthy engine, otherwise it just masks an idle problem by increasing the idle speed above specs and has no effect on anything once the throttle is opened.

Edited by - on

cks
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126 Posts

Response Posted - 09/07/2010 : 17:42:16

OP states that the motor's been idling rough. i've had a mercury 9.9 4 stroke outboard for the last 5 years and experienced a similar problem. Adjusting the idle screw works for me. It would be the first thing i'd check and takes less than 5 minutes to do. Who knows, maybe lightening will strike twice and it'll work for the OP.

Edited by - cks on 09/07/2010 18:17:07

Dave5041
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3758 Posts

Response Posted - 09/07/2010 : 19:40:46

He also said it was cutting out while motoring. That suggests a common problem through the range as more likely than an idle mix and a different running problem.

Edited by - on

DaveR
Master Marine Consultant

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2015 Posts

Response Posted - 09/08/2010 : 05:44:56

If after you've replaced any old fuel, replaced any old spark plug, made sure there are no air leaks and proved there's good spark you still have a problem, I'd make sure (if the carb bowl is metal) that the attachment arm is straight (bent down, not enough fuel, bent up too much fuel), check the jet seat to make sure it's not swollen (should not have rounded edges or look blown up) and as always, blow some compressed air through every orifice in the carb( removing the jet seat first so as not to blow it away).

Edited by - on

PCP777
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1225 Posts

Response Posted - 09/08/2010 : 08:09:14

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by jerlim
 Eric - you didn't say how old the motor is, or w/ how many hours of use...but our 2006 Merc 8hp, 4 stroke, with about 250 hours had similar issues, and finally would not start - which required our sailing back into the marina under head sail alone...the problem turned out to be ethanol related...check the 'fuel additives survey' thread in the General Forum for more details - but the short of it was salt deposits in the carb (from water in the gas) and gunk from a breakdown of the lining of the fuel line and the diaphragm of the pump - resulting in a costly repair...
<hr height="1" noshade id="quote"></blockquote id="quote">

Exactly. My 2007 9.9 Mercury 4 stroke had this same exact problem. Look at your fuel line. If the lettering is red, it's not rated for ethanol. Apparently the ethanol corrodes the fuel line which clogs the carb. I had to have my carb pulled off and cleaned as well as replace all the elements of my fuel line. If your fuel line lettering is blue, you should be OK.

Edited by - on

unclaimed baggage
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45 Posts

Response Posted - 09/08/2010 : 13:03:27

My line is grey and no lettering on it. I guess that it rubbed off?

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Stuff4Toys
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83 Posts

Response Posted - 09/08/2010 : 13:41:19

If you got the line with the engine in 2005 and it's a Mercury hose, it is better, but not completely ethanol resistant. Usually only the black lines will decompose and cause those problems. You should look into new fuel line anyway.

Still waiting to see if you checked a gas sample, did you change your spark plugs, or are you waiting for someone to waive their magic wand and fix it?

Edited by - on

jerlim
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1484 Posts

Response Posted - 09/08/2010 : 14:21:27

The grey line, supplied by Merc (at least in 2005), contains a 'special' lining, which I came to learn first hand, is not all that resistant to ethanol, and in fact was a major contributor to the issues we experienced...

Edited by - on

PCP777
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Response Posted - 09/08/2010 : 14:29:52

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by jerlim
 The grey line, supplied by Merc (at least in 2005), contains a 'special' lining, which I came to learn first hand, is not all that resistant to ethanol, and in fact was a major contributor to the issues we experienced...
<hr height="1" noshade id="quote"></blockquote id="quote">

True.

<blockquote id="quote">quote:<hr height="1" noshade id="quote">If you got the line with the engine in 2005 and it's a Mercury hose, it is better, but not completely ethanol resistant. Usually only the black lines will decompose and cause those problems. You should look into new fuel line anyway.<hr height="1" noshade id="quote"></blockquote id="quote">

The guy who fixed my engine was very specific, if your engine has the gray tube and it has the red lettering and you use ethanol you're going to have problems. My engine was bought in 2007.

Edited by - on

unclaimed baggage
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45 Posts

Response Posted - 09/11/2010 : 07:40:17

ok here is the outcome. I finaly made it to the boat yesterday, changed out the fuel with 100% gasoline and check the gap on the plug. The fuel line is the one that came with the motor and it does has red lettering on it.

It looks like the prob was the fuel. The RPM's were erractic at any throttle possition. After the last bit was out of the line itself the engine settled down.

Edited by - unclaimed baggage on 09/11/2010 07:41:06

GaryB
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4303 Posts

Response Posted - 09/11/2010 : 08:32:45

I still recommend replacing the fuel line. It's only a matter of time before it starts breaking down and will show it's ugly head at exactly the wrong time.

Edited by - GaryB on 09/11/2010 08:33:30

unclaimed baggage
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Response Posted - 09/11/2010 : 12:19:03

Great advice I plan on it.

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djdurrett
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124 Posts

Response Posted - 09/16/2010 : 10:38:06

I took my motor home last weekend. It is a 2007 model 5.5 merc 4 stroke. Took the carb off and took it apart. For reference, i have red lettering line, use stabil and run about a tank every two month through it. This is what I found: Carb Bowl had gray "jelly" like build up. And yes, there is an inline fuel filter. both the pilot (idle) jet and the main jet were almost completely clogged. And the motor has been running fine with a little rough idle. There was a fair amount of residue in the intake/backfire suppressor. I thought this motor was much too new to have buildup like this. I am on my way to get a new gas line, bulb and filter!

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Stuff4Toys
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USA
83 Posts

Response Posted - 09/16/2010 : 10:54:47

There you go, water and ethanol, the marine Stabil absorbed the water and it all fell out of suspension. Settles to the bottom in a gray goo.

Throw away the Stabil and look for a product that has NO ALCOHOL. Stabil has Ethanol and Startron has Methanol. Don't know if it is available universally, but look for a product called "Gas-Shok". If you cannot find it, let me know, I will put it on my web site and ship it to you.

Gas-Shok has NO ALCOHOL and will keep water & ethanol suspended for up to 8 months.

JOhn ><>

Edited by - on

Stuff4Toys
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83 Posts

Response Posted - 09/16/2010 : 10:55:38

Make sure you clean out your gas tank too!

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djdurrett
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Response Posted - 09/16/2010 : 12:15:47

This brings up the question: what do you do with old gas? Can't dig a hole and pour it in the yard anymore...

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John Russell
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Response Posted - 09/16/2010 : 12:30:39

DJ, I pour it into my truck when the tank is nearly empty then go fill up my truck. The "bad gas" mixes in with the fresh so much that it doesn't really have an effect on the truck's performance.

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