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Fuel pump difference

C

Capt80

New member
I have 1970 Mercruiser 140 GM 181 I/L4. I am replacing a leaking fuel pump, and have found and bought the placement pump. However the new pump, and all other pumps I found have a small difference to mine. The new pumps have the same fuel inlet and outlet, but they have a brass nipple on the bottom of the pump below the outlet port. The pump on my boat does not have this brass nipple. Every new pump I find has this nipple , but they all fit my boat. What do I do with this brass nipple? One diagram I found appears that they remove the nipple and put a brass screw there. I am new to the forum, and somewhat new to working on the motor. Any information would be appreciated!! Thanks
 
Perhaps your old pump is not a " marine pump "------I believe there should be a hose off that nipple to go to the air intake.-----It is a safety feature.-----Read up on it .-----Or perhaps invest in a parachute for your boating gear.
 
mechanical fuel pumps that dont have the "tell-tale" hose to the carb are not marine rated fuel pumps,
All menchanical fuel pumps need that vent to allow the diaphram to operate correctly, you cannot plug it.
The hose goes to the carb in case the diaphram ruptured and directs the gas into the carb preventing you from being blown out of the water
If you ever had a fuel pump in a car fail, you noticed it by the fuel leaking out the bottom of it, you really dont want that situation in a boat
 
Thanks for your input and responses. As I stated I am new to marine motors and trying get a handle on this. My present fuel pump has the incoming line from the fuel tank, and an outgoing line to the carburetor. The brass nipple is a third connection to the fuel pump. So does what you are saying mean that 2 lines need to go to the carburetor? I have a SELOC manual for my boat and it only shows the two lines in the diagrams. Thanks again for your advise!!
 
No , no ----that nipple only comes in service should the diaphragm develop a leak !!-----It is a safety feature.----Read up on it as stated already.
 
There should be a fitting of the same size on the carb or flame arrestor. You use a length of tygon (yellow) 1/4” hose for this...
 
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