puzzling carb problem

[ken-n-katie]

Hello all, My wife and I recently bought our first boat and it has a 1984 75 hp mercury. We have a very odd issue. The upper carb floods out near the butterfly valve......but here is the kicker. We took it off, hooked the fuel line directly to it and it held pressure fine. As long as it is not bolted to the motor, there are no issues. Any thoughts would be HIGHLY appreciated. I have been told the needle may be bad or that someone over-tighted the carb itself and it has a hairline crack that exposes itself when pressure is applied. Thanks, Ken and Katie

 

[hkeiner]

Re: puzzling carb problem

Perhaps the float was stuck and became unstuck while handling the carb during removal. You might consider installing and removing the carb a few times to see if you get consistent results (i.e., leak if carb installed and no leak if carb not installed). If the carb really only leaks when installed, I'll leave it to others to explain what might cause this. I can't think of any reasons.

The upper carb floods out near the butterfly valve......

If you can describe more precisely from where near the butterfly valve (shutter plate) the fuel is actually entering the throat, it might help narrow down the possibilities. I would guess that it is coming from one of the jet openings inside the throat.