Outboard Running Problems - SailNet Community
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post #1 of 8 Old 12-09-2007 Thread Starter
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Outboard Running Problems

Hi all,

I have a 6 year old Mercury 4.0 (2 stroke) horsepower outboard motor. It has always run fine, however I ran it for an hour maybe on regular gas this spring. Although, since then it has appeared to have no problems. This fall though the motor does not want to stay running. It will crank with the choke open but before I can put it on half choke it cuts off. And then if I try to start it on half or no choke the same thing happens.

Any ideas?


Catalina 22
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post #2 of 8 Old 12-09-2007
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If the motor starts but then shuts down, it sounds like perhaps a fuel related issue. I would first check the fuel filter for any debris that may be clogging the screen. This of course, world restrict fuel flow to the carburetor.

My tender's Merc 2-stroke did the same thing on two occasions within the past 8 years. Replacing the inline filter/valve solved the problem.

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post #3 of 8 Old 12-09-2007
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Open the carb "bucket" on the bottom of the carb, there is a screw there and clean. I have the same problem often.

Put a new spark plug and go.....
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post #4 of 8 Old 12-09-2007
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Such problems are almost always fuel related, as TB mentioned. We have had similar episodes and found that it often means pluggage in the jets of the carb. Old fuel or dirty fuel can lead to particles becoming lodged in these very small passages.
Fortunately these carburators are very simple devices and tearing them down to clean them is relatively simple... just don't lose any of the bits.
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post #5 of 8 Old 12-09-2007
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I just bought a tune up kit from a Mr. Bill Kelly of “Mastertech” here is his web site http://www.maxrules.com
He has an extensive web site. I intend to rebuild my outboard this winter using his replacement parts, a maintenance manual I bought off of Craigslist and the use of an engine shop a friend of my owns. My Evenrude 8 hp is running fine but it has been several years since the last time it was apart and it won’t hurt to go through it again.

It will help if you add fuel stabilizer to your supply of fuel and don't use old gas. I have a 10-gallon tank and it last me all season as I only motor a few hundred yards out of the marina. Even so I try to start my outboard at least twice a month and let it get up to operating temperatures for 15 minutes or so.

The following preventative tips seem to work well for me. I use fuel stabilizer in my fuel supply tank. Exercise the engine regularly and when I shut it down I disconnect the gas line and run the carburetor dry to keep the fuel from “breaking down” over time in the carburetor’s jets, passageways and chambers.

I don’t work for Mastertech but like his web site and the way I was treated.


Last edited by Northbeach; 12-10-2007 at 02:28 AM. Reason: word choice & sentance structure
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post #6 of 8 Old 12-09-2007
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Check for water in fuel...it's the most common of fuel related problem. To check, pour the contents of the tank into a transluscent container, e.g. a pastic milk or Poland Spring container. If the contents looks like salad dressing (separating as oil and vinegar do), you've found the source of your problem. We'll go from there on resolving it.

If not let us know, so we know that one is ruled out.
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post #7 of 8 Old 12-09-2007
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I assume you are using the internal tank on the engine...per Pub's suggestion...drain and refill with new gas/oil mixture.
You may also have some laquering of the carbeurator and or some water in the fuel bowl.
Try some carbeurator spray first...if that does not work, you may need to dis-assemble and clean it all out.
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post #8 of 8 Old 12-10-2007
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carb cleaner

Buy a can of carb cleaner.Drain out all of the gas,pour enough cleaner into the tank to fill the bowl a couple of times.Start the engine and run it until the carb is full of cleaner.Shut it down and let it sit overnight.Fill with gas and take it for a run.If the motor runs ok you won't have to take the carb apart.If it doesn't run ok it will be nice and clean when you take it apart.Use the type of carb cleaner that is flammable .Costs about 10 bucks.I saw this in a motorcycle magazine.Saved the guy $450(150 per carb for a mechanic to do it)

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