Fuel pump problems
 

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

Turn the bowl upside down adjust float to just start to rise with a 3/8 bolt slid between the float and the lower side od the bowl. Thast will get you very close to proper float level. There is a u-tube video from Holley on how to do this.
Good Luck

If you are sucking on the vent line going to the fuel pump you are putting neg pressure on the other side of the diaphragm inside the fuel pump and just not allowing it to operate at full capacity.....Picture a sub-woofer in a stereo system....when its in a box and it has a vent hole it can move in/out freely. If you plug that vent hole the sub will still move but if it moves less cause its working against that vacuum in the box now when it tries moving outwards.

Thank you ill try that...ill have to recalculate

Is that the way it should work..

That vent line coming from the fuel pump should go to the spark arrestor (air filter)...there should be little to no vacuum on that line. The only purpose of it is to flood the engine in case the diaphragm breaks inside that fuel pump. 9psi shouldn't be the issue.....ive used a small electric fuel pump on a carb before that put out 10psi and still worked just fine. Its the carb that the problem....most likely the float needs to be adjusted more.....unless the needle is sticking for some reason...

Zole, when you rebuilt carb, whose kit ? Sometimes the holley needle and seats seem to hold more pressure.

Also, fyi, parts aren’t as good as they used to be. If you search the net you’ll see several people with high psi problems with random aftmkt and oem mech pumps. If too much psi really is your issue, msybe an inline adjustable regulator may he your best bet. Especially since you being overseas. (Expense and amt time for shipping including returns)