Author Topic: Mechanical Fuel Pump Discrepancies  (Read 3663 times)

Offline WardaddysFury

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Mechanical Fuel Pump Discrepancies
« on: March 17, 2017, 07:08:50 PM »
Hey everyone,

First of all, I'm not too familiar with car mechanics work, but I'm pretty good when it comes to the application. So don't poke fun at me too hard if I ask a question that is pretty dumb. Amuse me haha

I just bought this 1980 K20 and my first goal is to get it running smooth. I'm going to be replacing the carburetor tomorrow, but I am also updating the fuel pump and lines to the carburetor. My engine is a 383 Stroker and I just purchased a Edelbrock 1721 Fuel Pump (performance). However, when I got started with the replacement of the old fuel pump, I noticed my old pump seems to have 2 input lines (I have dual tanks) and the single output. However, the Edelbrock only has one input and one output. Does anyone know what I need to do in this situation?

Thanks!
« Last Edit: March 17, 2017, 07:38:40 PM by WardaddysFury »
1980 Chevy K20 Stepside

Offline VileZambonie

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Re: Mechanical Fuel Pump Discrepancies
« Reply #1 on: March 17, 2017, 07:40:02 PM »
Regardless of dual tanks or single tank you still only have one feed line to the pump. One is the output to the carburetor, the other is the return. Some pumps do not have a return.

A stock pump is fine and I believe with the Edelbrock you will need to install a fuel pressure regulator as they are generally higher output
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Offline WardaddysFury

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Re: Mechanical Fuel Pump Discrepancies
« Reply #2 on: March 17, 2017, 07:43:56 PM »
Regardless of dual tanks or single tank you still only have one feed line to the pump. One is the output to the carburetor, the other is the return. Some pumps do not have a return.

A stock pump is fine and I believe with the Edelbrock you will need to install a fuel pressure regulator as they are generally higher output

Thanks for the reply! I got the fuel pump that only puts out 6 psi so it says that the regulator is not required. The only thing I would think go next is what to do with the return line. Do I just block it off?

Thanks again!
1980 Chevy K20 Stepside

Offline bd

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Re: Mechanical Fuel Pump Discrepancies
« Reply #3 on: March 17, 2017, 07:51:30 PM »
May I ask your reasoning for eliminating the return line?  Do you understand its purpose?
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline WardaddysFury

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Re: Mechanical Fuel Pump Discrepancies
« Reply #4 on: March 17, 2017, 08:14:04 PM »
May I ask your reasoning for eliminating the return line?  Do you understand its purpose?

Not gonna act like I know the exact purpose but I have a good idea for the reason for having it. I have a Edelbrock 1406 performance carb on now and swapping it with the same model. The vacuum line isn't installed so I won't be too surprised if the return line isn't installed on the carb, just on the fuel pump end. I'm up for advice, really.
1980 Chevy K20 Stepside

Offline bd

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Re: Mechanical Fuel Pump Discrepancies
« Reply #5 on: March 17, 2017, 08:58:09 PM »
The OE fuel pump 1/4" return line recycles a small percentage of fuel back into the fuel tank(s).  It makes no connection to the carburetor, whatsoever.  The augmented flow of fuel through the fuel pump helps cool the pump to prevent vapor lock and stalling.  The return line was used most commonly in 3/4- and 1-ton applications to compensate for the additional heat generated by the engine and exhaust due to the increased power demand and extended idling of engines in commercial applications.  The return line feature effectively makes the factory pump a high performance item for a 383 stroker. 

If your motivation simply is to enhance appearance, use -6 AN or -8 AN stainless steel braided hose and fittings to connect the OE pump to the carburetor, strategically anchoring the line with Adele clamps to avoid chafing.  Your 1406 carb flows 600 CFM on a naturally aspirated engine; it will never starve for fuel as a result of using an OE pump running a fuel return line.
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline WardaddysFury

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Re: Mechanical Fuel Pump Discrepancies
« Reply #6 on: March 17, 2017, 09:41:57 PM »
The OE fuel pump 1/4" return line recycles a small percentage of fuel back into the fuel tank(s).  It makes no connection to the carburetor, whatsoever.  The augmented flow of fuel through the fuel pump helps cool the pump to prevent vapor lock and stalling.  The return line was used most commonly in 3/4- and 1-ton applications to compensate for the additional heat generated by the engine and exhaust due to the increased power demand and extended idling of engines in commercial applications.  The return line feature effectively makes the factory pump a high performance item for a 383 stroker. 

If your motivation simply is to enhance appearance, use -6 AN or -8 AN stainless steel braided hose and fittings to connect the OE pump to the carburetor, strategically anchoring the line with Adele clamps to avoid chafing.  Your 1406 carb flows 600 CFM on a naturally aspirated engine; it will never starve for fuel as a result of using an OE pump running a fuel return line.

That makes a lot of sense. Thanks for the input. I am mainly switching to a stainless steel line because I am installing the Edelbrock hardline fuel filter kit seeing how my current fuel filter is resting comfortably on my valve cover and the fuel filter kit was free from a friend. Mainly switching to the stainless steel line so I don't have to purchase a new adapter seeing how the one I took off the old carb looked like a dog chewed on it.
1980 Chevy K20 Stepside

Offline WardaddysFury

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Re: Mechanical Fuel Pump Discrepancies
« Reply #7 on: March 19, 2017, 05:57:42 PM »
Update:

Replaced the carb, and saw that the distributor doesn't have a vacuum port so I left it off. Kept the old fuel pump until I figure out the return line issue. I've read a few forms from people who bought an after market fuel pump to see what they did. Some got a fuel filter that has a return line in it as well, and there is another one where he had a banjo fitting from the input fuel line on the carb. Still debating what I will do will research or take advice from here. Also, I noticed after tuning, that at idle my fuel can't keep up with the demand of the engine. When I'm going I have no issues. Still fine tuning.
1980 Chevy K20 Stepside

Offline bd

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Re: Mechanical Fuel Pump Discrepancies
« Reply #8 on: March 19, 2017, 06:18:16 PM »
If you decide to go ahead and install the Edelbrock pump, just cap the 1/4" steel line that runs back to the fuel tank.  If the truck experiences vapor lock, you can install a fuel pump with a return line nipple later and reconnect the line. 

What do you mean by this...

...I noticed after tuning, that at idle my fuel can't keep up with the demand of the engine....

Did you adjust the idle fuel mixture?
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline WardaddysFury

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Re: Mechanical Fuel Pump Discrepancies
« Reply #9 on: March 19, 2017, 09:15:58 PM »
If you decide to go ahead and install the Edelbrock pump, just cap the 1/4" steel line that runs back to the fuel tank.  If the truck experiences vapor lock, you can install a fuel pump with a return line nipple later and reconnect the line. 

What do you mean by this...

...I noticed after tuning, that at idle my fuel can't keep up with the demand of the engine....

I'll leave it alone for the mean time. I live in Denver so vapor lock would be easy to achieve her. Figured out the problem with the fuel upkeep while at idle, turns out my vent line was capped off so it was creating a vacuum.
Did you adjust the idle fuel mixture?
1980 Chevy K20 Stepside