Mercury 4.5hp leaking gas

1979 Mercury 4.5hp, serial 5272411

Previous owner said it ran fine, just leaked gas out of the bottom of the carb. OK, bought it and immediately bought and installed a carb gasket kit. Still leaked gas. Changed all the fuel lines and replaced all the hose clamps. Changed the fuel connector, and the o-ring, spring assembly inside it. Still leaked. There are 2 screws or "plugs" as the manual calls them on the bottom of the carb. I took those out and gave them a coating of Permatex Form-a-gasket sealant, and re-installed them. Still leaks. Every gasket on this thing has been replaced.

The fuel is leaking someplace from the bottom of the carb. I have ran it for an hour or better with the cowling off and I can not see anywhere on the middle/top of the fuel parts where gas is leaking. Has to be on the bottom.

I have attached an exploded view of this carb from the manual. Im not sure what else I can do? Any suggestions?

Re: Mercury 4.5hp leaking gas

I have the same motor and same problem. It turned out on mine there is a small rubber line that goes from near power head and runs toward the front of the motor. It was cracked and leaking. Drove me nuts. Been awhile since i have fixed it and i kind of forgot exactly. But recheck it and see. It doenst really look like a fuel line, its small like car vacume line. It leaked under the carb and kept making me think it was the carb. let me know if this helps you. I will try to take cover off mine and look again. Joe

Re: Mercury 4.5hp leaking gas

That has got to be it. I would have never looked there. I went out and checked on my motor, pulled off that hose, and yes sure enough this little hose is cracked at the bottom and wet with gas!

Now, the next step is to find out what this thing is called. I cant find it on a parts diagram for this motor/model. I have attached 2 pics of it. The first pic is where it attaches to the top of the power head and the second one is where it is leaking at the bottom.

Does anyone know what this is called? I know the part I need is the hose, but what is the purpose of this hose?

Re: Mercury 4.5hp leaking gas

Man, i think you just answered my question, and perhaps solved my motor not starting problem. My motor is identical to yours and its leaking gas under the carb as well, the motor won't start even though i've rebuilt the fuel pump and carb and sprayed a whole can of carb cleaner into this thing, still nothing except that fuel leak, it did run for about 5 seconds once. I've changed fuel lines etc with no help so after reading your post, i think the longer hose on my motor is also the culprit, its the only hose i haven';t changed because i didn't know what purpose it served either, but, now i think its an integral part of getting the fuel to the spark plug area to run the motor. In a couple of days i will know for sure, when i finish these twelve hour shifts and get time to work on it again.