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Jason, Marine Mechanic
Category: Boat
Satisfied Customers: 16209
Experience:  Degree in Marine Technology. Gas and diesel marine mechanic.
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I have a 1997 Mercury Mariner 15 Hp outboard. This engine has

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I have a 1997 Mercury Mariner 15 Hp outboard. This engine has had excellent maintenance and has always ran well. However it would sometimes boug out when you gave it gas. Last year the motor appeared to be bouging or flooding its self out. The motor would start but once you gave it gas it would flood out and quit. I have overhauled the carb and checked the timing. I have changed gas and checked filters. I purchased this motor new. What would cause this motor to do this.

My name is XXXXX XXXXX I will be helping you today. Most questions will involve troubleshooting, and usually take many posts back and forth.


It still sounds like a carb issue. When you overhauled it, did you remove it and fully dissasemble it, down to pulling every jet out? And using spray carb clean and compressed air to clean it? Along with using a new carb gasket kit when you put it back together? Did you set the float height correctly?


Also, did you happen to check your compression yet, and if so what did you get?

Customer: replied 5 years ago.
Yes the carb was totally taken torn down with new gaskets. I did not set float height, just checked to see it was loose .Yes I checked the compression, I don't remember what it was but thought it was good.

These are realatively complicated little carburators.


You did the fuel pump portion when you did the carb correct?


Have you checked to see if the primer circuit of the carb is working? When the engine runs, is the blue button all the way down or all the way up? When you put this carb back together, did you work from a shop manual, or a good shop manual diagram to make sure you got all the gaskets/diaphrams/springs/and checkballs on the carb, fuel pump portion, and primer portion all in the correct spot?

Customer: replied 5 years ago.
I don't know, This work was done by a graduate of the Mercury School in Florida.

MMI in Orlando? Or Wyotech?


You need to have the carb redone by an actual certified Mercury technician. Wyotech grads are a bit better than MMI grads. But with either of them, when they graduate from those schools, they are not actual certified technicians. All they have is a piece of paper that states they went to that school.


Now with the engine. If it is flooding out it is the carb or the fuel pump causing the problem. With this particular carb it is all one unit. If it was redone, it does not sound like it was done properly. Or.... and this is scenario 2. Your boat has trash in the fuel tank, and you do not have a fuel water seperating fuel filter on the engine.


When you do carb jobs on boats you have to inspect the fuel supply. Make sure there is no trash in the fuel tank. If there is, it will find its way right back into the carb again. Clogging it, again.

When ever I do carb jobs for people I reccomend (and nobody ever tells me no) a fuel water seperating fuel filter kit. The fuel filters that come on the engines are the equivelent of filtering fuel through panty hose. Not very good. The better filter kits filter down to 10 microns, and they also catch water.


That would be my advice to you. Have the carb done by an actual certified tech. Check the gas tank for trash. And install that fuel water seperating fuel filter if you do not have one.


Post back with any questions

Good luck!


Jason and other Boat Specialists are ready to help you
Customer: replied 5 years ago.
The gas tank and lines were completly cleaned. I know this because I did it myself. I did this before I had the carb over hauled. It appears I wasted my money with the carb over haul. The motor will start right up but will flood out when you give it gas. Could I try just setting the carb And if so how do I set it.

Now when you say flood out, does gas pour out of the front of the carb, or does the engine just stall? You said flood, so I was assuming gas was coming out of the front of the carb.


Also, do you have your engines serial number handy?

Customer: replied 5 years ago.
No gas does not come out of the carb, Engine just kind of pops and stops. The engine serial #0G479669
Is it popping out of the exhaust, or out of the carb? Can you tell? It makes a difference so I ask.
Customer: replied 5 years ago.
I believe it is popping out of the exhaust

Popping out of the exhaust indicates a rich fuel condition, incorrect ignition timing, or poor compression because of a piston problem.


Now compression on this engine needs to be about 90 psi or better to run properly. Run a compression test on your engine and see what you get for numbers.


Base ignition (idle) timing needs to be 8 degrees before top dead center. What is your timing set at?

Customer: replied 5 years ago.

I do not know what the timing is set at. The newly graduated Teck set it . I will have to ask.

Thank You

Your very welcome. That 8 degrees is pretty specific, and it has to be set right at 8 or you can have problems with it.