What I learned about mechanical fuel pumps, and the safety overflow hose.....

[Lou C]

OK I had just rebuilt my Q-Jet and still had the 30 year old Carter mechanical pump on it. Well I replaced that petrified old yellow tygon hose for the fuel pump overflow, and in a few days, I saw what looked like gas in the new hose! So of course I replaced the pump with the Sierra one I bought a few years earlier in anticipation that this old pump would give up sooner or later. A few days later I got curious. And checked that fitting on the pump after taking it apart.......what I found was that it was totally plugged up with some sludge like black crumbly stuff. There was no sign at all of gas in the lower chamber and the diaphragm was still in good shape. Not sure where this sludge like stuff came from but it was a bit oily, smelled faintly like gas/oil. BUT, if there was really a gas leak, I can't see how you'd notice it unless you got way down low and really looked because the only trace of gas, was a tiny bit in the lowest part of the hose way down by the pump. So anyone who has one of these style pumps, might want to replace that tygon hose and keep and eye on it.

I cleaned out the crud in the passage and sure enough you can see if that diaphragm fails, there is a passage that will let the gas out into the hose, but not if its plugged up with whatever that crud was....

 

[Bt Doctur]

What everyone call a "tell-tale", overflow hose, fuel pump failure hose is there for 2 reasons. 1 being a safety issue incase the diaphram ruptures , 2 a vent for the diaphram. Without it the diaphran cant pump fuel.

 

[Lou C]

Thinking back it’s possible that there was gas in the lower chamber but it may have drained out after I removed the pump. You can still get the original Carter style pump, from Carter themselves or Sierra.

 

[Sea18Horse]

Timely topic!

Just yesterday I got to taking a more critical look at the fuel pump in my 65 Owens project having gotten a lot of the more pressing matters taken care of. And as I suspected it is a regular old automotive fuel pump. So my questions are what size is the vent nipple on your typical SBC marine fuel pump? Just eyeballing it in pictures I'm thinking 1/4"? What size hose do most folks use?

And has anyone come across a good fitting or nipple arrangement to adapt into a flame-arrestor? Seems neither my flame-arrestor nor my (automotive seemingly) Q-jet has a provision for the tell-tail hose.

Cheers..........................Todd