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SpeedAgent 04-17-2009 08:32 AM

Poorly Running 9.9 Merc Outboard
I've searched for advice on my outboard issue and all of the results seem to be conflicting.

I have a 2001 Mercury 9.9 outboard on my Catalina that I bought in November. When I bought it the engine would start fine, but once I got going at 1/3-1/2 throttle the engine would eventually bog down and then turn off. Restarting was not possible unless I started it in gear, but then it would eventually cut off. The choke would change its running habit, but only for seconds, then it would turn off again.

I changed the plugs a few weeks ago and initially it ran super and I thought the problem was fixed. A couple of sails later and it runs the same as when I bought it. It initially starts great and it will idle just fine, but once I get going it will bog down and turn off and restarting is nearly impossible unless in gear.

I'm pretty frustrated at this point. The original gas that was in the tank when I bought it has been exchanged and fresh gas/oil mixture is running in the tank. I'm sure the plugs are fouled, but I have not confirmed that, only an assumption since it is back to running poorly.

I have a manual for this engine, but don't know where to start and don't have time to rebuild anything on my own. Can anyone suggest anything simple to check or am I in for a carb rebuild? At this point I can't sail this boat since I am fearful of not being able to return to dock.

Thanks in advance,


sailingdog 04-17-2009 08:41 AM

Given that you don't know the age or status of the spark plugs, changing them with new ones is probably a good start. :) Rebuilding and cleaning the carburetor is also probably good idea.

Lostmt 04-17-2009 09:00 AM

I had the same problem. The last time it died was in the ICW with tons of tow and power boat traffic with a head wind. No way to tack out to open water. Very hard on the nerves.

Here's what I did.

1. Cleaned and added another fuel filter. Glass see through.
2. Cleaned the carb. Lot of green junk growing in the carb.
3. Changed the fuel and add Star Tron. I would not recommend Sea Foam.
4. Got new plug. Recommended by the Suzuki. That way I know I have the correct plugs.
5. I now keep a can of spray carb cleaner on the boat.

My 8hp Suzuki 2 stroke is still a little hard to start but runs fine now. Once its warmed up it starts on one pull.

You might find one of your dock mates that will clean your carb for you. One of mine did it for me and only took about 30 minutes. I watch him and now I know how to do it myself. If I had taken it in it would have cost me a couple hundred bucks.

raisin56 04-17-2009 10:44 AM

I too had a similar problem, it turned out to be that the ethanol gas had loosened the varnish that had built up in the fuel tank. As the engine ran the debris would build up around the strainer in the tank and choke off the fuel flow. Shut down the engine and it would drop clear and all work fine for awhile. I had to empty the tank and flush it clean, replace all filters and hoses. Then run a tank of gas with carburetor cleaner in it to finish the job.


Lostmt 04-17-2009 11:03 AM

Here some information on ethanol fuel problems. Sea Foam also contains alcohol.

It can be purchased at WalMart in the boating section.

sailingdog 04-17-2009 11:20 AM

Be aware that ethanol blends are not as stable as the previous MTBE based gasolines. :) The ethanol tends to absorb water from the humid air and once it reaches 1.5% water by volume or so, it phase separates out from the gasoline, leaving you with fuel that has an octane rating of somewhere around 80...

timebandit 04-17-2009 11:33 AM

Two stroke or four stroke?

Lostmt 04-17-2009 11:37 AM


Originally Posted by timebandit (Post 476585)
Two stroke or four stroke?

It doesn't matter. Ethanol fuel will cause problems. Same with any additive that contains alcohol.

escapaide 04-17-2009 12:06 PM

I had a similar problem and found that if i squeezed the promer bulb on my fuel line it would continue to run, i assumed the fuel line had a smal air leak and replaced it and the motor runs fine now

svHyLyte 04-17-2009 01:29 PM

I had the same problem with a 2001 15hp version of the engine (up-tuned version of the 9.9)--so much so that I bought the 5 year warranty from Mercury before the original factory warranty expired. The motor made 5 trips back to the dealer in Sarasota without improvement. The 6th trip--to another shop-proved the fix. It seems that there is a small adjusting screw on the carb that needs be adjusted "just so" (it's actually described in the owner's manual as pointed out by the tech at the second shop). With that adjusted properly, the engine seems to work fine. Without--Not. I would say that its a mixture control but when I suggested that, the tech said it wasn't so I don't know what it actually moderates. It's above and somewhat to the right of the carb barrel as you're facing the motor from the normal user position.


s/v HyLyte

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