Fuel pump vent line?

MG777 · Post by **MG777** » Thu Jun 11, 2015 1:46 am

Hi everyone I noticed a fuel/oil leak from under the nut where the vent line should be connected. Ido not have a vent line only the nut that is open and usually the vent line should be attached to it. This is the nut that is holding the leaver. What should i do with this nut should i iscrew a second nut that will close the whole instead of the non existing vent line or is there a special adjustment nut?

oilleaker1 · Post by **oilleaker1** » Thu Jun 11, 2015 6:10 am

If you close off the vent attachments, the diaphram in the fuel pump won't be able to move. What about a short line to the other hole? In, Out connected in a circuit? All mine are hooked up as shown in diagrams.

Post by **wesk** » Thu Jun 11, 2015 9:01 am

If you have fuel or oil leaking at the vent port then either one of your diaphragms is failing or you have a stuck PCV valve or a fording valve inadvertantly in the fording position and the oil is being blown out from the crankcase. Either way step one is to fix the leak. Step 2 is to decide how to secure that port.

That port must be left open to perform it's vent function. If you do not wish to run the vent lines required for the fording system then just install a vented cap on that port just like the Army did.

This is the late M38A1 setup where the fording system plumbing is not installed. Instead they installed the small round vented fitting cap shown to the right of item N. This vented cap is part No. 5196397.

MG777 · Post by **MG777** » Sat Jun 13, 2015 10:53 am

Thank you very much for your responses. I have one more question concerning the fuel pump primer handle located on the fuel pump . In what position shall the handle be set?

I tried searching for the vented cap however i could not find it... Do you maybe know an online store where i could order it? Or is it maybe a universal part that I could get at a home depot?

Again, Thank you for you response!!

Post by **wesk** » Sat Jun 13, 2015 12:32 pm

You can leave it in any position.

One of our members found them in Canada and had them for sale here on our For Sale Board. Search the board. Use the key words, "nipple, ball check, fitting, 7375063, special"

RonD2 · Post by **RonD2** » Sat Jun 30, 2018 10:17 pm

Just wanted to confirm what I read above. My fuel pump came with a vent (same as used on the differential covers) over the fitting that holds the primer handle in place. I'm using the vacuum side of the pump just for wipers --- no fording valves are installed.

In my current confusion, this photo shows a plug I installed in place of the vent, thinking the pump needs to be "closed" at this point because of the two "in and out" vac lines going up to the manifold and wipers. Haven't run it yet, getting ready to do that. If I understand this thread correctly, I need to take the plug out and put the vent back in? Your advice appreciated as always! Looks like this:

RonD2 · Post by **RonD2** » Sat Jun 30, 2018 11:01 pm

I think I answered my own question. Plug needs to go. Vent needs to be there for when wipers aren't operating. Wiper valve closed would stop air flow through the vacuum pump, probably not a good thing.

Amazing what a few quiet minutes can do....should've had them 10 minutes before asking the goofy question....