Need help on understanding the new type Airtex 4657 (M3120) Fuel Pump

[Larry E.]

Just got my Airtex 4657 in that had a few surprises with it. First off I got this for just a back-up
to the original one (AC) that is on my 66 Base Engine Coupe. I will buy another original AC one
when the time presents itself. In searching the threads it tells us the pin that holds the arm some-
times work itself out. This problem looks to be fix as the pin is now inside the casting to hold it
tight. (See Pictures Below) There is also some type of tube that is cast in the front of the pump
body. There is a pin or some type on line in this tube that can be pulled out and in with a rubber
type cap. (Kinda looks like a Dill Tire Cap) You can hear what appears to be some type of valve
closing and opening. Don't have a clue what this is for. Does anybody know what this is? (Picture
below) Not happy this came with the pump but for a back up I can live with it. Need some comments
on this and thanks>Larry P.S. Of course the instruction sheet does not mention the tube.

[Richard M.]

Re: Need help on understanding the new type Airtex 4657 (M3120) Fuel Pump

Larry, That port is a safety feature for Marine applications. A small hose connects to that and is routed up to the carburetor flame arrestor/air cleaner. It's a US Coast Guard requirement for inboard marine engines. Appears Airtex has it covered for both auto and marine use.

If the atmosphere side of the internal rubber diaphragm should ever fail because of a rupture or pinhole, any fuel vapors or liquid fuel would be sucked into the carburetor as opposed to dripping down into the bilge and create a fire hazard.

Leave that cap off for a automotive application. The sound you hear is the diaphragm pumping air.

Rich

[Larry E.]

Re: Need help on understanding the new type Airtex 4657 (M3120) Fuel Pump

Rich: Thanks for the response but if that is the case how does one use this Pump in an Auto application>
What setting
Pushed in or Pushed out should be used? The sound I'm hearing sounds like some type of valve inside clicking.
Thanks>Larry

[Richard M.]

Re: Need help on understanding the new type Airtex 4657 (M3120) Fuel Pump

Larry, Ok I thought it was just a cap. I looked on their website Document section but nothing there.

Probably best to contact Airtex directly. Here's their Contact page.

https://airtexasc.com/contact-us/

Rich

[Larry E.]

Re: Need help on understanding the new type Airtex 4657 (M3120) Fuel Pump

OK;Just got off the line with the Fuel Pump people from Airtex. He was unsure why my inlet in this
casting moves in or out but he said just remove the rubber cap or take the whole tube out and it will
work for Auto Use. All it is a vent for the pump. Larry

[Richard M.]

Re: Need help on understanding the new type Airtex 4657 (M3120) Fuel Pump

Good you got the info Larry. As suspected, that vent is for a hose for marine use. All pumps need a vent for the diaphragm to breathe. Most have a small hole in the top housing.

Rich

[Larry E.]

Re: Need help on understanding the new type Airtex 4657 (M3120) Fuel Pump

Good you got the info Larry. As suspected, that vent is for a hose for marine use. All pumps need a vent for the diaphragm to breathe. Most have a small hole in the top housing.

Rich

Rich>Thanks for the help on this. BTW>This pump is one of the strangest looking pumps I have
ever seen! Larry

[Gary B.]

[John D.]

Re: Need help on understanding the new type Airtex 4657 (M3120) Fuel Pump

In older days the Airtex 4657 pump was almost identical to the AC pump except no AC on it.
Long ago I used a new Airtex pump for parts to rebuild my original. Worked perfect.
When rebuilding/restoring any of the fuel pumps it is not necessary to remove the pin holding the "blades" in. Leave that alone. John D

[Larry E.]

Re: Need help on understanding the new type Airtex 4657 (M3120) Fuel Pump

In older days the Airtex 4657 pump was almost identical to the AC pump except no AC on it.
Long ago I used a new Airtex pump for parts to rebuild my original. Worked perfect.
When rebuilding/restoring any of the fuel pumps it is not necessary to remove the pin holding the "blades" in. Leave that alone. John D

John: Thanks for the comments. Too bad they went to this design;wish it would have stayed the same. BTW>In researching
the fuel pumps I came across GM#5621638>AC#4445 which still can be bought. Do you know anything about this pump?
I think it was used in the C1 early days. Wonder is this would work for a base engine 1966? Larry