2013 Mercury 20 1F20201HK Leaking gas out the carb mouth (Solved)

[Venomous]

Hi All, Working on a Mercury 20 Outboard for a friend. Carb was originally leaking out the overflows. Rebuilt the carb and now float valve is closing properly and no gas leaking from the overflows. I put the carb on the bench and hooked it up to a 3-4 psi electric fuel pump. With the fuel pump running it did not leak any fuel at all. After the test, the bowl was filled with fuel. So I know for sure the float valve is working properly.
When you try to start the motor, after a second or two of the motor turning over gas starts to drip out the front mouth of the carb. If you hold the throttle open it will start, but gas continues dripping out the mouth of the carb. I have taken the carb apart again. And everything seems to be in great shape and working properly. We even bought a new carb and it does the same thing. Any ideas? Thanks for any help.

 

[alldodge]

Welcome
Readjust float so fuel is shut off a slight bit lower

 

[Venomous]

Welcome
Readjust float so fuel is shut off a slight bit lower

I would love to do that, but it does not seem to be adjustable. Both the factory carb and the new cab have floats entirely made of plastic. There are no adjustment tabs like I usually see on carb floats. Is there a way to adjust these? Thanks for the response.

 

[alldodge]

Have not seen a entire plastic float until now
https://www.crowleymarine.com/mercury/products/162532-float
Needle
https://www.mercruiserparts.com/809570002-float-valve

Need maybe @Texasmark or @racerone help

 

[alldodge]

I don't see it in the part number breakdown but wonder if a spring should be on the needle. Found where a Gen carb has a spring installed
At 2:47 you can see the spring

 

[Fun Times]

I’d have to guess you have too much feel pressure now from the engine fuel pump ?.

That or a ruptured fuel regulator or pump whatever the design is on your engine model.

 

[Venomous]

I don't see it in the part number breakdown but wonder if a spring should be on the needle. Found where a Gen carb has a spring installed
At 2:47 you can see the spring

Yes, that was something else I found strange in addition to the all plastic float. Most float valve needles have a built in spring at the top of the valve. These float valve needle pins are solid. After working on ATV's and SXS's for years I have quite a selection of carb rebuild kits. I went through them trying to find a float valve needle that matched the dimensions, but had the spring in the top. No such luck.

 

[Venomous]

I’d have to guess you have too much feel pressure now from the engine fuel pump ?.

That or a ruptured fuel regulator or pump whatever the design is on your engine model.

I did read about someone having a similar issue where his fuel pump was putting out to much pressure. This pump should have 4.2 psi according to the service manual. I tested it with a fuel pressure gauge and got 4psi. I have not seen a reference to a fuel regulator in the service manual. I do not believe it has one.

 

[Venomous]

In addition to the one person I read about with the fuel pump issue, I found another guy that had the same issue I am facing. No one could figure it out, he took it to private mechanics , then he finally broke down and he took it to 2 different Mercury service centers and no one could figure it out. He finally bought a new carb and that fixed it. I put a new carb in this one and it still does it.. I am really stumped here.

 

[alldodge]

I put a new carb in this one and it still does it.. I am really stumped here.

If you still have the old carb, might try this.
Remove float and get a hair dryer or heat gun. Heat the plastic up so it will bend just a slight bit. Other then that I'm also clueless

 

[Venomous]

If you still have the old carb, might try this.
Remove float and get a hair dryer or heat gun. Heat the plastic up so it will bend just a slight bit. Other then that I'm also clueless

I still have it. I was thinking of taking a small flat soldering iron tip and using a low enough temperature to slowly bend the plastic. I will try this and see how it goes.

 

[Venomous]

Solved!!!! Hi All, I tried to adjust the original float by heating but gave up after looking at it. The way the float is built it would have been highly unlikely I would have been able to adjust it and still have it grip the top of the float valve. I studied each and every part from the air intake all the way to the engine. There is an insulator between the carb and the intake manifold. It has a gasket on either side of it. The gaskets looked perfect but they did look a little thin to me. I ordered some Tohatsu replacement gaskets and they were noticeably thicker. I installed them. Problem Solved. The engine must have been sucking air from around the insulator. This lowered the vacuum in the throat of the carburetor that still let the engine draw gas up into the carb , but not enough vacuum to suck all that gas into the cylinder. Some would drip out the mouth of the carb. Now it runs perfectly with no leaks.

 

[Venomous]

If someone reads this post with the ability to change the title of this thread, please add the word Solved to the title. Thanks

 

[Chris1956]

I am skeptical that you have fixed the cause, with the insulator gaskets. I hope you got it. However, your issue is almost always a bad float, inlet needle and seat or adjustment problem. best of luck.

 

[Venomous]

I am skeptical that you have fixed the cause, with the insulator gaskets. I hope you got it. However, your issue is almost always a bad float, inlet needle and seat or adjustment problem. best of luck.

I was skeptical also. So, after the new gaskets seemed to work....I put the old gaskets back in and the the leaking out the mouth started again. Since putting in the new gaskets the boat has been out on the water twice and no leaking. I am hoping it stays this way.. If the problem rears it's ugly head again, I will be back...lol

 

[Chris1956]

Carbs work on the Bernoulli principle. Higher velocity air has a lower pressure, than lower velocity air. So if gas was sprayed thru the carb jets into the throat, because of that low pressure, I would think it would then be sucked into the engine, using the same airstream.

I would expect the insulator is there to keep the carb cooler and therefore to control vapor lock. If the gaskets were leaking, the air flow would be less thru the carb, and less fuel would be sprayed into the throat.

OK, a theory, say your inlet needle leaks a bit under the fuel pump's pressure. This forces fuel into the carb throat, but with your leaking insulator gaskets, not enough air was going thru the carb throat to pull that fuel into the engine. New gaskets sealed the air leak and therefore increased the vacuum in the carb throat and the extra fuel was sucked into the engine and burnt.

If the theory is correct, the problem should reoccur as the inlet needle wears more. Fuel economy of the engine should suffer.

You might check the spark plugs and see if they are overly black with fuel. Ideally you want light to dark brown deposits on the spark plugs. Just .02