can I increase return line on mechanical fuel pump??

[thaifighter]

Im in the middle of a restore on my truck and will be running new fuel lines. currently Im running mechanical fuel pump , retun line size 1/4" with a holley 600
Im tossing around the idea of running holley avenger 2barrel tbi unit with the electric fuel pump that requires 3/8 return so as to have zero pressure ideally. My question is will the old stock mechancal fuel pump opperate properly with a bigger retun line?? I would like to have the option to swap between mechanical and electric fuel pump or tbi and carb.:guile-1: thanks in advance

 

[chengny]

You may get different opinions on this, but in my experience;

A GM stock, cam driven/diaphram type, mechanical fuel pump does not require a return line.

I routinely run the 2 port version pump - or a 3 port with the return capped - and never have a problem. The existing return line back to the tank(s) gets dead-ended.

You could dedicate the return line to your electric pump and tee the suction and discharge lines to service both pumps.

I guess you will install isolation valves to segregate the two pumps when switching over from mechanical to electric and vice-versa?

 

[oneluckypops]

You may get different opinions on this, but in my experience;

A GM stock, cam driven/diaphram type, mechanical fuel pump does not require a return line.

I routinely run the 2 port version pump - or a 3 port with the return capped - and never have a problem. The existing return line back to the tank(s) gets dead-ended.

You could dedicate the return line to your electric pump and tee the suction and discharge lines to service both pumps.

I guess you will install isolation valves to segregate the two pumps when switching over from mechanical to electric and vice-versa?

Correct.

The earlier pums had 2 ports, suction and discharge to the carb. They did NOT have a return line, later years they added a return line for emmissions compatability, the pump pressures didnt change. Bigger fuel return line will not hurt what you are doing, how ever if you run a smaller 1/4" line on your tbi you will most likely have problems with high pressure and then cause the regulators to fail.

 

[chengny]

They did NOT have a return line, later years they added a return line for emmissions compatability, the pump pressures didnt change

Perfect - couldn't have said it better!

 

[thaifighter]

Perfect! as far as isolating the pumps I was just going to unplug the inline pump and filters and run a section of braided line in their place, but a bypass valve sounds like a good way to go too! lol .......Thanks again!

 

[wildcatjason]

Are you going to just run a mechanical pump all the time? Won't this ruin the seals in it by running it dry and it is just extra friction loss for no reason. I'm not understanding the reasoning for this just to switch to a carb. People run electric pumps and carbs all the time. Maybe I'm missing something.

 

[Guardian]

Jason is correct. If you run the mechanical pump dry it will cause a diaphram failure. The gas acts as a collant as it passes through the pump.

 

[thaifighter]

I wont be running the mechanical pump if i go to tbi it will be removed and plated off. the question was just regarding the 1/4" stock return line size and if it alters the action of the mechanical pump if increased.

 

[Jims86]

Why not just run the TBI pump, and mount an external regulator that you can just tweek real quick after choosing carb or TBI? You can Cap the regulator and the return on the TBI, Then only use one feed line for both... you still need the ruturn line for the regulator.

Skysurfer is running a setup like this on his TBI, and it is working very good.

 

[thaifighter]

well Ive thought about going with the bypass reg, but if I dont shift over from carb to tbi I would prefer to stick with the mechanical pump less finicky more durable less filters to run and change, easier to change pre carb filter and one less electrical part that may choose not to work one day when Im in the bush ...but cheers!

 

[Jims86]

BTW...stay away from the Holly and Edelbrock TBI units, they are not very friendly to field servicing. A unit from an 87-93 454 would be the way to go for a large barrel TBI.
Just an FYI IF you do choose TBI.

 

[thaifighter]

when you say field servicing are you refering to changing out parts like injectors and aic? I sure like to hand held programer that holley has with thier system eliminating the need for laptop tuning .

 

[Jims86]

when you say field servicing are you refering to changing out parts like injectors and aic? I sure like to hand held programer that holley has with thier system eliminating the need for laptop tuning .

If thats the route you want to go, I highly recommend the FAST 4 barrel TBI.
You can get a Holly computer and harness, and purchase an oem 454 unit...all you need to do is wire it up.
the holly and edelbrock TBI units are the same ones they sell as direct OEM replacements, but they leak, and if you need to replace an injector, you cant walk into NAPA or a GM dealership and get replacements, much less seals or "o" rings.

 

[Guardian]

I have considered something along those lines, but don't like the injector location.