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return line to tank

wazzabie

wazzabie

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Why is there a return line to the tank on a 78 K5 blazer? I do not have the smog pump.

I do have the heater duct that goes to the air cleaner.

Also what typr of fuel hose should I use on this?
 
wazzabie said:
Why is there a return line to the tank on a 78 K5 blazer? I do not have the smog pump.

I do have the heater duct that goes to the air cleaner.

Also what typr of fuel hose should I use on this?
Click to expand...

Just because it doesn't have a smog pump doesn't mean it didn't have at least a vapor can when new . Probably had EGR too on the original intake .

Even though 78 had no cats over a certain GVWR .
 
wazzabie said:
Why is there a return line to the tank on a 78 K5 blazer? I do not have the smog pump.

I do have the heater duct that goes to the air cleaner.

Also what typr of fuel hose should I use on this?
Click to expand...
My 76 has a return line to the tank from the fuel pump. Was mechanical though I've since replaced it with an electric pump.
 
You have a return line because GM figured out that constantly running fluid through the fuel lines, and back into the tank what wasn't used, prevents (or almost completely prevents) vapor lock.
 
No. Longevity seems to be about the same, installing one requires more money if stock, etc.

EFI requires electric (with exceptions, since there are now apparently mechanical pumps that create/hold constant pressure) so it really depends on what someone is trying to do as to whether they want or need to use electric or not.
 
So, is there an issue with plumbing a carb setup such as a Quadrajet or Truck Avenger with a dead-head line and no return if you have a mechanical fuel pump?

I wasn't planning on running a return. If I should, then I'm not sure how to plumb the return . . . ?
 
That's why GM has multiple mechanical fuel pumps...three+ fittings, it's a return system. Two lines, no return.

IMO you really, really want a return system on the fuel pump. GM doing it should be enough justification, but you don't want to set a system up, then find out you have to get another pump and run more line because you get vapor lock.

Not every vehicle will have problems with vapor lock, plenty of years no return was used, but this is a better safe than sorry deal to me.
 
even with an electric pump you should use a psi regulator with a return line as well. It helps tremendously with keeping vapor lock and percolation to a minimum because the fuel reaching the carb is much cooler than if it sits in the line and soaks up heat.
 
xanthias said:
So, is there an issue with plumbing a carb setup such as a Quadrajet or Truck Avenger with a dead-head line and no return if you have a mechanical fuel pump?

I wasn't planning on running a return. If I should, then I'm not sure how to plumb the return . . . ?
Click to expand...

I have a truck avenger and with the return line plugged off the carb floods everytime I give it throttle and then let off. I hooked up the return line and it ran fine. the pump pumps fuel if you are using it quickly or slowly. its got to go somewhere. if the extra can't go back to the tank then its gonna go in the carb.
 
Chas, thanks for your answer. I don't want to hijack, but if you could reply or PM with details on how you plumbed the return, I would really appreciate it.
 
my truck had a return line originally. when I switched to a fuel cell I simply disconnected it at the pump and plugged off the rubber line coming from the pump. I just hooked it back up to the pump and ran a braided fuel line from the top of the cell to the hard line on the frame. its not a lot of pressure, just enough to find the leak I had were the line rusted through. :doah:
 
(Apologies to OP, just tell me and we can take this to PM if this isn't helping you)Okay, your setup sounds exactly like what mine is going to be, HollyTA, mechanical fuel pump and fuel cell. Original tank had a fuel return line.

So, fuel line out to mechanical pump. Mechanical pump through filter and pressure regulator to carb. Return line port on mechanical fuel pump back to fuel cell.(?)
 
On a somewhat related note, what pump are you using chas, aftermarket or factory? I`m new to the carb scene, but my buddy tells me alot of aftermarket mech. fuel pumps don`t have returns.
 
pauly383 said:
Just because it doesn't have a smog pump doesn't mean it didn't have at least a vapor can when new . Probably had EGR too on the original intake .

Even though 78 had no cats over a certain GVWR .
Click to expand...

I had this since new. It has the cat but no smog pump and no vapor can.

IT does have the heat riser to the air cleaner. It came with the cold climate package.
 
new question to add

let me bump this to the top.

I have an edelbrock fuel pump and no return on it. the k5 this motor is going in has a return line, how can I hook this up? get a pressure reg with a return on it? thanks
 
on my 1976 jeep I am working on, the return line is actually on the factory fuel filter. I am not sure if that will work for you but it does for my jeep, with a 304v8.
 
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