Replacing the Carter mechanical fuel pump on one of my old cars.

I found basically the same pump at Summit and it was delivered today. It appears identical but has a fitting for a vent(?) on the upper pump body (see pic showing old and new pump). The old pump has a hole there but no fitting. Should I ignore this apparent vent tube or cap it? Thanks.

Could be a reference for a supercharger.
follow the links to the Supercharged Studebaker for someone doing just that
http://racingfuelsystems.myfunforum.org/viewtopic.php?f=28&t=1032#p9568
edit: well looks like PB issues on the supercharged thread, but the other linked thread for a Carter 3508S still has pictures with a referenced pump.

That was my first thought, too. I guess you can take the Studebaker from the boy but you can't take the Studebaker out of the boy.

It's the "weep" hole so you can tell when your diaphragm goes bad. Don't plug it. Run a hose off of it or pull the fitting out.

Also maybe to prevent fuel from getting into crankcase from a ruptured diaphragm.??

Joe

Not a weep hole.

It's a vent for the diaphragm, nothing more. You only want pressure or vacuum on one side of the diaphragm, the fuel side.

Putting fuel pumps on Mopars since the 60s.Never ever saw one with a fitting like that.Guess it would not hurt but sure is strange.One reason I use Holleys.had like 3 bad carters that were total junk.Rocky

yea. well when was the last time you saw a boost referenced supercharger on a Chyrsler v-8?

A lot of different fuel pumps that share the same mounting pattern use the same castings. If the nipple was a "breather" that means the top of the diaphragm would be isolated from the engine crankcase but they're normally exposed to the crankcase...that's where they "breathe". A shot of the lever end might show if it's isolated.

The only time I've seen a nipple in that location is for supercharger reference i.e. when the supercharger boost exceeds the pump pressure, the supercharger boosts the spring in the pump.

Still it's a "hole" that will "weep" or "vent" fuel when your pump goes bad.

If you get a leak out that hole your first indication will be a non-running engine followed by an oil pan full of gasoline. BTDT with no leak out that hole whatsoever.

Probably not visible without partial disassembly. The seal appears to be on top of the diaphram spring.
Agree that would be the difference between a boost ref for supercharger and vent line for something like marine use.

It is actually listed as a marine fuel pump...

There ya go!

so it is just a vent? Install the pump and don't worry about it? Send it back and get another model?

Just called Summit tech support about this.

They say it is a vent used in marine application to send fuel/vapor up to the carb and out of the engine housing in the event that the diaphragm ruptures. They further say the vent does not access the engine oil so an oil leak will not be an issue.

Yep, Marine applications use it. You do need to leave it open. The pump needs that vent on the air side.