He guys...I have a problem on my friend boat.He heas a 7.4 mercruiser with a holly 4175 carb.He heas problem with flooding from only one bouvl on the seckundary part of the carb.I mesured the fuel press and at idle is 9 psi.The fuel pump is monted on the block and it is black color.The vacum on the pump is conected to the port vacum on the carb the line is god no vacum leak.Can you tell me is the pump pumping to much fuel and is there a diffrent pump thet goes on the engine with less psi...thank you

there should be no vacuum on the line going to the pump its a vent line that is there so if the pump fails the fuel goes into the carb not the bilge

Ok...tell me what to do...change the pump??

Another thing...wen i take the vacum line and put it in my mauth and suck a bit the presure drops

Sometimes 9 is okay. I’d change the needle and seat first. In fact, if both haven’t been changed in 5 yrs or more, i’d change both.

and x 2 on the fuel pump vent. It goes to s vent on carb or flame arrestor, not vacuum port. A vent port can look like a vacuum port, so check it.

That is what happens, So don’t hook to vacuum. Again, that post is to vent. In cars it would be a hole with no barb fitting nor hose. Vented to atmosphere. If diaphragm leak, fuel goes to ground. In a boat, if diaphragm leaks the fuel must go to carb or your boat goes boom !

I have changed the needle and seat and put a nitrofil float ewerithin new.Why does he not flood the primary part of the carb only the secundary.

Maybe the float is set too high.

Ok..can you tell me why the press drops wen i suck on the vacum hoes.I can regulate it with my mouth on 5 psi and it does not food then

I put the float paralel to the bowl.It lifts up yust a bit and closes the fulel ven i test it in my hand