3 fitting mechanical fuel pump question?

[daveodom]

Swapping out my 230 six for a 350 v-8 in my 64' c-10. Went into O'riellys and picked up a mechanical fuel pump. 350 was out of a 88' blazer, so that's the pump I got. My question is: pump has an inlet fitting and an outlet to the carb. It also has a third fitting coming out of it. Made for a 1/4" hose. When I went to start the truck fuel came out of it. I plugged it off and everything seemed to be good. Is it a return line or what?! Can I just tee it back into my supply line from the tank? Thanks

[Merchant67c10]

Yea that's a return, you can do either plug it or send it back to the tank

[rickf]

Do such pumps by any chance have an internal pressure regulator?

If yes, then that return line might be a "spill over" line, and plugging it might effectively disable the pressure regulator.

I have no idea if that is how it works or not, just speculating.

Actually, just asking the question, is that by any chance how it works or is that just a "spare" supply line?

-rcf

[Blazer1970]

Or just buy a pump for say a 1970 350 which only has two ports.

[myraley]

Or buy a fuel pump like mine, 75 big block. It has 4 lines! An in, an out, a return, and a I dunno what the heck its for so lets just cap it off, ok?

[joe6pack]

-Not to hi-jack this thread but keep it going
I just swapped a 454 in place of a 250 in a 1978 swb and it has the return line but the truck does not -so naturally I plugged the extra line so I could do a burn out or 10
Now the problem is I take it for a hot lap and it pulls HARD thru the first 2 gears of the TH400 but soon after it hits drive it dies
Then I get to pull over and look like a douche and crank it over until it blows smoke and fires back up and runs ok
Could the pump be flooding the carb? -I frantically pump the gas to get it started so I don't if it's too much fuel or not enough
Basically I'm just trying to get info on how the return side being plugged could effect the pressure under these conditions
I am going to try using fresh gas in the other tank and see if the pickup might be the problem as the truck sat for a while before I got it
I will probably buy an in/out 2 port a NAPA for $30 and try it too
Just asking so we can all sort this variable out of the equation

[Longhorn Man]

every time I have capped off a return line, the pump ended up leaking later.
I would look for a 2 line pump.

[Prong]

Get one equipped for a manual tranny truck--they are the 2 line setup.

[bamabaxter]

Napa part # M6624 2-port
part# M6626 3-port

[bamabaxter]

pm if you ever need prices or part#'s

[oldrusty]

I had a fuel pump issue which may be along this thread...its been resolved by Plan B, but still curious. I swapped out the beat-to-heck 400 sb for an 65 'vette built 350. When we tried to put on the fuel pump from the 400 into the place on the 350 that was clearly for a mechanical pump, the pump didnt work! No gas, no nothing. I got a 350 pump from AutoZone, it looked totally the same...and didnt work. Why would this be the case? Arent these things the same? Cam wasnt changed for something that fits differently in the 350, so...?

In the end, I put on a high flow racing pump, and got a holley return line regulator. Havent put on the regulator, but...live in eternal hope. Be nice to have an explanation tho.

[joe6pack]

I just replaced the fuel filter in the quadrajet and dialed in a hotter tune
The thing is kicking ass! -with the same old fuel pump
I guess I will leave it alone unless it acts up again
Still curious about how the return line works

[Captainfab]

Originally Posted by oldrusty

I had a fuel pump issue which may be along this thread...its been resolved by Plan B, but still curious. I swapped out the beat-to-heck 400 sb for an 65 'vette built 350. When we tried to put on the fuel pump from the 400 into the place on the 350 that was clearly for a mechanical pump, the pump didnt work! No gas, no nothing. I got a 350 pump from AutoZone, it looked totally the same...and didnt work. Why would this be the case? Arent these things the same? Cam wasnt changed for something that fits differently in the 350, so...?

In the end, I put on a high flow racing pump, and got a holley return line regulator. Havent put on the regulator, but...live in eternal hope. Be nice to have an explanation tho.

All small block fuel pumps are interchangeable. Could it have been an issue with the pushrod not contacting the pump arm. Although I don't know if you could actually tighten down the pump if it wasn't. So I assume you're running an electric fuel pump now?

[oldrusty]

Thats what I thought, since I got a new one from Autozone, and it looked IDENTICAL! I think the pushrods are also one of those parts that didnt change over a long period of time too...

Yes, I found a racing fuel pump on craigslist...it was on a mitsubishi fuel injected thing, and I didnt realize that a FI pump put way more flow through than one for a carb engine...so I got a holley regulator that shunts the overage back to the tank. Its been brutally hot, so if I am doing anything its going to happen within a small window of time in the evening. Building a garage is on the list, but hasnt happened yet! We got everything but the return line connected, I need to figure out where it comes into the engine compartment...I also need to wire it up to something that will turn on when I turn the key, so the pump can run for a a few seconds before I try to crank the motor...any input?

[Captainfab]

If you want to go with the electric pump, I would suggest wiring it in using a relay to power it. You can get fuel pump relay kits from both Jegs and Summit....and possibly your local auto parts.

[shadetree]

This thread got hi-jacked, but in an attempt to bring it back on track: daveocom, did you get a 2 port pump? Did you cap off the return line of the 3 port?

[joe6pack]

I'm still having the problem at WOT
I guess the pump is overpowering the float with the return plugged
Is putting the return to a T on the inlet of the pump an option?
I guess we should all get the 2 port if there is no return line and save a lot of B.S. end of story.

[bamabaxter]

I have a question about all of this, the 3 port pumps are usually for automatic transmission vehicles, and the 2 ports were for manual, that is what the parts catalog says.....why is this, can someone explain?

[dragn91]

my old truck i swapped a 350 into had the 3 fittings one was inlet outlet and a return i just ran a return line back to the tank drove it daily for two years and it never had a problem once

[bamabaxter]

I am asking why the 72 chevy calls for a 3 port for automatic and a 2 port for manual. Other than the ever so common, "it has something to do with emissions" statement, I am trying find out the actual purpose.

[LostMy65]

I Googled: 'fuel pump 3 ports'
This thread popped up.
Exactly what I was looking for, but still seems partially unanswered.

I put a 350 out of a 79 pickup in my 66.
The Mechanical Fuel Pump on it has the three ports.
Some said they just plugged the third.

That's what I did also.
I noticed today that my fuel pump is knocking.
I know it's the fuel pump - I isolated the location of the sound using a short piece of hose as a Stethoscope.

I might of missed it, but is there a harm in plugging the 3rd fitting?
Could this be adding too much back pressure - causing the knocking noise?
Or could it be causing these performance issues that some others here have mentioned?

Obviuosly; if my fuel pump is going out, I'll be getting a new one with only two ports, but it'd still be nice to know if there's a problem with plugging the third port.

[WIDESIDE72]

Back from the dead! I am having a similar
problem. I installed a blazer tank in my 72 SWB. I have a 3 port pump. I tried installing a 2 port pump but the fuel line to the carb won't line up.

I capped off the return line and the truck ran for a while then quit. It just came back from 2 yr paint jail. I did the blazer tank Install at the same time, so I can't really isolate the problem. Plans are to run a return line back to the tank next week...
Posted via Mobile Device

[Woody Johnson]

Originally Posted by joe6pack

I'm still having the problem at WOT
I guess the pump is overpowering the float with the return plugged
Is putting the return to a T on the inlet of the pump an option?
I guess we should all get the 2 port if there is no return line and save a lot of B.S. end of story.

I would like to know more about the "Tee" idea? Why couldn't one simple put a tee in the inlet line and loop the return right back into the inlet instead of running it back to the tank? Seems plausible to me. Does anyone know? For sure?

[storm9c1]

The return lines were supposed to help with vapor lock and fuel boiling in the lines -- by returning the fuel to the tank, it helps to cool the fuel and the fuel pump itself (pump can't get heat soaked when the fuel is constantly moving).

If you just tee it back to the inlet, I'd imagine you would do the opposite of cooling the fuel, you will keep applying heat to the fuel since that area is up by the engine where you would just keep circling the fuel. I think the pump and the fuel would start to heat soak. I would not recommend that. This is an old thread, but some suggestions were to replace it with a 2-line pump. That's the route I'd recommend as well if you cannot have 3 lines.

FWIW, I believe the even crazier 4-line pumps had something to do with emissions controls (ie: the charcoal canisters in the 70s and 80s), but it's been a while since I worked with one of those setups, so I can't recall for sure.