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post #1 of 9 Old 07-21-2013 Thread Starter
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Outboard fuel leak

I have a 6HP outboard mercury model ME5ML 2003

I can start it but after it starts fuel pours out the hose barb at the end of the green arrow.

I know very little about outboards but I'm pretty sure they are supposed to pee water not gas.

Not shown on this picture is another similar hose barb on the other side of the carburetor. Also not connected to a hose.

Did someone not connect something?
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post #2 of 9 Old 07-22-2013
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Re: Outboard fuel leak

That is an atmospheric vent for the float bowl. It should have gasoline vapor only. You have another carbureter problem. That fitting should lead to a screen, filter or cannister someplace away from the hot stuff. Some of them just led through the cowl (pre emission days). Or it could just lead back to a fitting on the atmospheric side of the throttle plate.

Your basic problem is somethig wrong with the float needle control system. Dirty-worn needle, float fuel saturated,bent-broken float support,all come to mind.

If you aren't familiar with carb work in general get a repair kit for it. It should have all necessary parts and specs in it. Be clean!!

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post #3 of 9 Old 07-22-2013 Thread Starter
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Re: Outboard fuel leak

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Originally Posted by Mechsmith View Post
That is an atmospheric vent for the float bowl. It should have gasoline vapor only. You have another carbureter problem. That fitting should lead to a screen, filter or cannister someplace away from the hot stuff. Some of them just led through the cowl (pre emission days). Or it could just lead back to a fitting on the atmospheric side of the throttle plate.

Your basic problem is somethig wrong with the float needle control system. Dirty-worn needle, float fuel saturated,bent-broken float support,all come to mind.

If you aren't familiar with carb work in general get a repair kit for it. It should have all necessary parts and specs in it. Be clean!!
Thanks

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post #4 of 9 Old 07-22-2013
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Re: Outboard fuel leak

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I have a Tohatsu 6HP 4 stroke, maybe the same motor? Maybe a stuck float needle? A few taps on the float bowl might free it? Easy, not too hard! The other possibility is that the external tank only vents incoming air. I discovered this on a hot day in the sun. When I opened the filler cap I got a big whoosh of outgoing air, LOTS of pressure, which may overcome the float valve?

I fixed it by removing the small rubber "duckbill" one way valve from the center of the cap. No more sprayed gas on my hands when disconnecting the hose. You might try running with the filler cap off to see if you still, get the overflow. If so, it is probably a stuck float valve.

Paul T
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post #5 of 9 Old 08-07-2013
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Re: Outboard fuel leak

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I have a Tohatsu 6HP 4 stroke, maybe the same motor? Maybe a stuck float needle? A few taps on the float bowl might free it? Easy, not too hard! The other possibility is that the external tank only vents incoming air. I discovered this on a hot day in the sun. When I opened the filler cap I got a big whoosh of outgoing air, LOTS of pressure, which may overcome the float valve?

I fixed it by removing the small rubber "duckbill" one way valve from the center of the cap. No more sprayed gas on my hands when disconnecting the hose. You might try running with the filler cap off to see if you still, get the overflow. If so, it is probably a stuck float valve.

Paul T
An update on this: After removing the one way duckbill valve on the cap, when squeezing the primer bulb with the now two way vent open, I heard what appeared to be bubbles blowing inside the tank and the bulb would not "firm up".

I also noted that it was taking about 4 or 5 more pulls to get the engine started. After closing the vent the bulb would "firm up" after 4 or 5 squeezes.
So, it appears the bulb pressurizes the tank instead of actually "pumping" the fuel?

So, looking back at what I did, I think an easier solution to getting sprayed gas on your hands would be to just loosen the whole filler cap before disconnecting the fuel lines.

As mentioned in an earlier post, after sitting in the hot sun the tank built up a whole lot of pressure as the original cap only vents air into the tank, not out. If this is a concern you could just loosen the filler cap a bit to relieve the pressure instead of modifying the one way vent, like I did. Why didn't I think of that in the first place?

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post #6 of 9 Old 08-07-2013
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Re: Outboard fuel leak

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So, looking back at what I did, I think an easier solution to getting sprayed gas on your hands would be to just loosen the whole filler cap before disconnecting the fuel lines.
Paul T
We figured this out also (the hard way). This also solved our spraying gas issues.
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post #7 of 9 Old 08-07-2013
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Re: Outboard fuel leak

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We figured this out also (the hard way). This also solved our spraying gas issues.
From another post:

Tohatsu troubles

Last entry

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post #8 of 9 Old 08-07-2013
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Re: Outboard fuel leak

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From another post:

Tohatsu troubles

Last entry

Paul T
Didn't see that last post you made there. I was thinking about doing the cap modification noted. Glad I did not, whew! Thanks!
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Re: Outboard fuel leak

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Didn't see that last post you made there. I was thinking about doing the cap modification noted. Glad I did not, whew! Thanks!
The only down side is that it appears to effect how the primer bulb works. It takes some extra pulls to get it started. The other thing I noticed is that after trolling very slow for a long time the motor starts to die, which it didn't do before I modified the cap. So maybe it needs the pressure in the tank to help get the fuel up to the motor? At any speed above that, no problem, I guess the fuel pump can manage?

Anyway, it was a $50 mistake. Unfortunately, I have always had the tendency to want to "tweak" things, to make them "better". Don't know why I didn't think of just loosening the cap, duhh!!

Paul T
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