[joshbarnett]

The tapered face in the back of the hole identifies this as an inverted flare, like steel brake or fuel line.
5/16" steel fuel tubing has 1/2-20 threads on the nut.

Original application would have had a steel hard line, bent 90° as close to the nut as possible, so that the line goes up the front on the engine in front of the passenger side head / behind the alternator.

If you want just a hose barb, it will be 5/16" male inverted flare to 5/16" hose nipple adapter fitting..
Any place that makes hydraulic lines should have the fitting.

Any auto parts store decently equipped should have also had it......but things today aren't what they once were as far as inventory on hand....

Excellent. What a frustrating search this turned out to be. Now that you said "5/16" steel fuel tubing has 1/2-20 threads on the nut", I remember it swapping a fuel pump on another vehicle. Why the hell I thought it was a hose barb, I have no idea. Went to AutoZone, nothing in stock. Had them look up the pump, couldn't tell me what thread it is. Spent 2 hours driving around to no avail. Anyway, thank you.

 

[joshbarnett]

Looking at the old pump in the first picture I don't think he has room for a straight barb.

He may have room for a piece of 3/8 tubing that turns around 120 degrees back towards the crank then goes up and after a few more bends goes into a carb. Need the flaring tool and highly recommend 3/8" nicopp due to all the bending that will be required.

Or just use a stock line which probally has the correct fitting and bends for a stock intake/carb. I would make room for the stock line with a BFH. But that's me.

Good point. At least now I'm on the right track knowing what I am looking for is a flared tube with a flare nut. I was looking exclusively for a hose barb this whole time and the specificity of the size has made it very hard to find.

 

[joshbarnett]

Oh and what didn't matters is running into this. Shows a pump looking identical to what I am installing:

https://www.stockwiseauto.com/carter-m4685-mechanical-fuel-pump?Year=1986&Make=Chevrolet&Model=Monte%20Carlo&srsltid=Ad5pg_H_ROK92vHGi0L_aGKdhhEXzanIPqDxscnnyKi1uFBonR5AU4eg6S8

It says the outlet fitting thread size is: 5/8-18 UNF-2B in.

So that confused the hell out of me and whoever else I asked.

 

[cerial]

I linked this at post 18. It should work just fine with no modification as it is very similar to your old setup. You may find it on amazon etc with faster shipping.

https://www.jegs.com/i/JEGS/555/51996/10002/-1?gclid=CjwKCAiAoL6eBhA3EiwAXDom5vYyEEiqvMLYRBMwt7b_Xw24M-XGohVgMrsOKUGFmKdySn7LRygWEBoCG48QAvD_BwE

 

[ericnova72]

It says the outlet fitting thread size is: 5/8-18 UNF-2B in.

So that confused the hell out of me and whoever else I asked.

5/8" - 18 Unified National Fine (UNF) is the nut size for 3/8" inverted flare hard line.

 

[joshbarnett]

I linked this at post 18. It should work just fine with no modification as it is very similar to your old setup. You may find it on amazon etc with faster shipping.

https://www.jegs.com/i/JEGS/555/51996/10002/-1?gclid=CjwKCAiAoL6eBhA3EiwAXDom5vYyEEiqvMLYRBMwt7b_Xw24M-XGohVgMrsOKUGFmKdySn7LRygWEBoCG48QAvD_BwE

Didn't wanna wait for shipping so I contrived my own. Bought a 5/16 flare nut and got about 2 inches of 5/16 copper line, double flare one side and bubble flare the other, back in business. I know, I know I am not supposed to use copper for fuel lines...

 

[MikeTudor]

There should be no fuel above the line where the upper and lower halves of the pump body are screwed together.....so obviously the pump diaphragm is leaking / torn / pinhole.
If it is managing to come out that small hole , that means it is also being pumped into the crankcase since the opening to the pushrod side is a hundred times bigger.
Check your oil for being fuel contaminated now.

The parts of the diaphragm edges you can see outside the housing do look a little swollen and ragged.
Possibly ethanol exposure incompatible?

it's a rebuildable pump, you can get a kit to replace the pump diaphragm.....rather than just replacing the pump.

Pump looks like it follows the original Carter design. Everybody makes a clone of it. Originally based off a early Corvette pump.

Carter 888562 Carter Fuel Pump Rebuild Kits | Summit Racing

View attachment 628475

new fuel pump is about $20, how much is that diaphragm? Seems a lot easier to just replace the pump.

 

[MikeTudor]

AutoZone sure didn't.

Edelmann 822560

 

[MikeTudor]

Noticed today that the mechanical fuel pump is squirting fuel out of this hole when running:
View attachment 628473

Does anybody have any idea as to what that hole is even for? I plugged it up for now to stop the leaking, but would certainly like to find a permanent fix.

You plug it gas goes in your oil pan

 

[MikeTudor]

Didn't wanna wait for shipping so I contrived my own. Bought a 5/16 flare nut and got about 2 inches of 5/16 copper line, double flare one side and bubble flare the other, back in business. I know, I know I am not supposed to use copper for fuel lines...

Buy a short 5/16 brake line.

 

[2old2fast]

new fuel pump is about $20, how much is that diaphragm? Seems a lot easier to just replace the pump.

Good quality mechanical fuel pumps start about $50 & go up from there ..

 

[MikeTudor]

Who's are good quality?

 

[MikeTudor]

When you tear apart the pump check the inside for casting defects/cracks.

Lets say there are 6 in a mold and a ram injects aluminum into the mold. If there are any voids CRACK, then the thing is pulled from the mold and thrown into a vat of water/oil if it slams the side of the vat on the way in CRACK, up some type of belt to a press where the channels between the pumps that allowed the liquid aluminum to flow to all the pumps are sheared off, if the 6 are not set into the press correctly two may be destroyed but that will also pull the other 4 making a less noticable CRACK, removed from the press they are sometimes set in a box but usually thrown into a bin(more dent then crack) .

The tops follow the same basic pattern and the two pieces (5-7pieces total) are usually assembled off site. There may be some slag/trim removal or cleaning but for the most part stress cracks can easily happen.

If the part is coated so it looks like chrome thats may reveal cracks or voids before assembly. But if just raw aluminum things can get overlooked.

So it could be a cheap easy to replace diaphragm. But I am leaning towards the posiblity if a casting crack at or near that weap hole or next to the edge of the diaphragm. If you bolt a new diaphragm in and it still leaks then that will confirm a crack even if it is easily overlooked.

WHEW!!!!!

 

[RAYFIN]

I see no reason to run a mechanical pump on anything.

 

[MikeTudor]

I see no reason to run a mechanical pump on anything.

Electric fuel pump=John Deere;o)

 

[ericnova72]

new fuel pump is about $20, how much is that diaphragm? Seems a lot easier to just replace the pump.

Maybe because it's a higher output, street/strip compatible pump that is rebuildable and has clock-able inlet and outlet port locations, along with a high rpm anti-float spring....might make it worth rebuilding?

Rather than a $20 throw-away crimped together replacement pump, that may not make the volume or pressure needed?

The diaphragm is $18

 

[MikeTudor]

Is it a higher output pump? Average carburetor GM car is around 5 to 7 PSI. is he running a high-output motor?

Amazon.com: EASYBERG Replacement Chrome Mechanical Fuel Pump with Compatible with SBC Chevy 305 350 400 : Automotive

Buy EASYBERG Replacement Chrome Mechanical Fuel Pump with Compatible with SBC Chevy 305 350 400: Mechanical Fuel Pumps - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

www.amazon.com

 

[joshbarnett]

Maybe because it's a higher output, street/strip compatible pump that is rebuildable and has clock-able inlet and outlet port locations, along with a high rpm anti-float spring....might make it worth rebuilding?

Rather than a $20 throw-away crimped together replacement pump, that may not make the volume or pressure needed?

The diaphragm is $18

Oh there is no doubt I will be rebuilding it. If for no other reason than to have it as a spare part. Thanks for the link. Btw, Summit is the only place where you can buy just the diaphragm. Other places sell a full rebuild kit for around 60 bucks.

 

[MikeTudor]

https://www.ebay.com/sch/i.html?_nkw=fuel%20pump%20diaphragm&norover=1&mkevt=1&mkrid=711-34002-13078-0&mkcid=2&mkscid=102&keyword=fuel%20pump%20diaphragm&crlp=_2-1300-0-1-1&MT_ID=&geo_id=&rlsatarget=kwd-77378263987895:loc-190&adpos=&device=c&mktype=&loc=78073&poi=&abcId=&cmpgn=329851879&sitelnk=&adgroupid=1238050244979164&network=s&matchtype=p&msclkid=07772c170c4a162f87134fc6d20b0185

 

[realcarsrob]

Basically it's a breather hole to allow a normal air pressure on the back of the diaphragm. It also signifies that there's a crack in the diaphragm. Buy a rebuild kit and make it a new one again.