HELP Carb overflows with fuel line disconnected!

[tonkit]

I have a 1982 Merc 115 Tower of Power that I purchased about a month ago and have been working on ever since. Most recently I have had fuel issues. The latest issue is the bottom carb overflows gas out the throat when I pump up the primer bulb. So far I have:

​1. replaced all fuel lines from the gas tank to the fuel pump.
2. replaced all fuel lines going to the carbs.
3. rebuilt the fuel pump
4. rebuilt the carbs
Put carbs back on and #3 (bottom) carb still overflows. Took apart and re-checked float setting all was good. Found small leak in float.
5. Today I replaced the float, re-checked the float levels, blew through the inlet line with seat held closed I couldn't get any air to go past and with needle open the flow was good. Put back together and #3 still overflowed when the primer is pumped up (it doesn't have to be pumped hard).
6. I removed the bowl cover with the needle and seat in it and pumped some gas into the bowl. Float seemed to float fine. I then held the needle closed and pumped the primer bulb and no gas came through so the seal is good.

Now, you're not gonna believe this (at least I didn't). With the fuel line to #3 disconnected and plugged when I pump the primer bulb FUEL STILL LEAKS FROM THE THROAT OF THE #3 CARB.

How the heck can this be? There is no fuel to the carb? I repeated this several times and can come to only one conclusion. There must be another way for fuel to get into the carb throat. Maybe through the crankcase?

Help! Where do I go from here?

Thanks guys!

 

[flyingscott]

Check the vent on the carb itself

 

[tonkit]

OK so now I know how the carb can overflow without the fuel line hooked up. Carb re-build was good ( I have done enough carbs in my life that I am very meticulous ). The previous owner, not mechanically inclined, thought that maybe the boat wasn't starting because it wasn't getting enough fuel so he turned the knob on top of the little brass thingy with the fuel line running to it.

​Apparently if you open the fuel enricher all the way it will allow fuel to flow through the pump and out the bowl of the top carb down to the enricher and, since the valve had been manually opened, on down to the intakes thus overflowing through the carbs. Since the fuel feed for the enricher is in the bowl of the top carburetor the needle and seat won't stop fuel from flowing.

OK, today I really learned something new. Hope this helps someone else here in the future.