# 25 HP Mercury Flooding



## JonBoat (Jan 13, 2013)

I have 1998 25 HP Mercury that is flooding. Rebuilt carb, lowered float to the point it would not even run, Idle screw is all the way in. Raws gas comes out in the water. I purchased it used and it has been that way since I purchased. Checked compression 110# on top, 115# on the bottom. Runs good at WOT, 28 mph GPS on a 1448 jon boat. It has th e same symptoms as the You-Tube video with 8 parts. I appreciate any advise...

JonBoat


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## crazymanme2 (Jan 14, 2013)

Pretty straight forward carb.Maybe you have some dirt in your system that keeps getting in the needle.


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## JonBoat (Jan 14, 2013)

Thanks crazymname2. I should have listed that I have changed fuel filter, etc. Probably ran 30 gallons of fuel through the motor. Also the timing is 6 degrees BTDC at idle. I have exhausted every avenue I know to take with the fuel. The motor was previously owned and I can tell the carb had been off and apart. I was wondering if someone left out one of those little parts, but I cannot tell. After you run the motor for a while at 1/2 to WOT it idles correctly, but really fast until it starts flooding. I am trying to figure out if it has an internal problem before I spend more money and time. Any advice is appreciated..


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## cincinnati (Jan 14, 2013)

Float valve sticking open. Cheap fix!


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## MDCrappie (Jan 14, 2013)

cincinnati said:


> Float valve sticking open. Cheap fix!



Yep - only 2 parts that shut off the fuel. Needle and Seat. Take carb off, removed bowl, dry carb. With mouth blow thru fuel inlet and air should pass. Slowly raise the float to level and the air flow should stop. If the air doesn't stop then the needle/seat is not sealing.


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## JMichael (Jan 14, 2013)

If it's only flooding at low rpm/idle, then a leaking float valve is a very real and likely possibility. 



MDCrappie said:


> cincinnati said:
> 
> 
> > Float valve sticking open. Cheap fix!
> ...



Using this method is not a good test. Even an extremely worn out needle can be made to seal with the amount of pressure that can be applied by a finger pressing up on the float. The amount of pressure applied by the float trying to rise in a float bowl full of fuel is very minimal and nearly impossible to simulate and get correct using your finger to push the float up. A closer simulation might be to flip the carb upside down and let gravity and the weight of the float close the needle but even that isn't fool proof.


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## JonBoat (Jan 14, 2013)

Thanks for the advice. I have replaced the needle valve, but will give it another look and make sure the shuts off. Can the seat be replaced?


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## JMichael (Jan 14, 2013)

If the parts breakdown shows a parts number for a seat or (needle and seat set) then it should be replaceable.


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## crazymanme2 (Jan 15, 2013)

> I have replaced the needle valve, but will give it another look and make sure the shuts off. Can the seat be replaced?



Yes.I have replace them.


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## CaseyP (Jan 15, 2013)

If your float is plastic, it could have a crack in it that your not seeing, filling up with fuel not letting it operate correctly, metal floats will do that too. I would put a new float in it and go from there.


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## JonBoat (Jan 15, 2013)

Thanks guys .. Doesn't look like there is a part for the seat only the needle valve. I will try replaceing the float. Let everyone know the results once I get some parts...


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## JMichael (Jan 18, 2013)

JonBoat said:


> Thanks guys .. Doesn't look like there is a part for the seat only the needle valve. I will try replaceing the float. Let everyone know the results once I get some parts...


Be sure to clean/polish the old seat if you can't replace it. Here is one method I learned several years ago that works well. You can take a wood dowel that's small enough to fit down inside the seat. Chuck it up in a cordless screwdriver/drill, spin it and sand the tip of the dowel to the same profile as the tip of your needle. Now insert the down into the seat, apply a little pressure and spin for a min or so. That will clean and polish the seat.


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## Charger25 (Jan 18, 2013)

Have you checked the fuel pump? could be a cracked diaphragm .


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## crazymanme2 (Jan 18, 2013)

> Have you checked the fuel pump? could be a cracked diaphragm .



A cracked diaphram won't pump fuel & motor won't run at wide open throttle.



> Runs good at WOT, 28 mph GPS on a 1448 jon boat.


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## Charger25 (Jan 19, 2013)

crazymanme2 said:


> > Have you checked the fuel pump? could be a cracked diaphragm .
> 
> 
> 
> ...




yeah, forgot about it running at WOT. Was thinking about it spittin out raw fuel. Mine did start and run with a cracked diaphragm though.


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## CaseyP (Jan 26, 2013)

Just wondering if you got the problem solved yet?


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## injunjoe (Jan 27, 2013)

I am also wondering if you got this problem fixed.

I also wanted to ask if you recently replaced your fuel tank.
The new tanks are made to hold 5 lbs of pressure before venting unlike the older style tanks.
If a fuel demand valve is not used the pressure will build up and flood the carb.

My solution to this problem was to just replace the new fuel tank cap with an older style vented cap as I did not want to buy the $29.00 fuel demand valve. I feel the valve is just something else to go wrong and cause headaches.


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