I just got to looking under the 69 bird I just purchased and noticed that the fuel return line runs out of the fuel pump and has been capped off back by the gas tank. I know that in 2004 the tank and sending unit were replaced with a new 69 GM?Camaro units. Also the car has a Holley Avenger 570 Carb and a Performer Manifold. Is this setup OK or should I work on getting the return line hooked up?
More than likely the sending unit that was used did not have provisions for a return line. You'll need to get the correct sender, unless it is just capped off at the tank as well. It was done for some reason...let's all take a moment to speculate...
I drive a 69 with a brand new tank, no return line...holley 650 carb ,400 engine....just make sure you have a "vented cap" to the tank...I have no problems with my set up
2012 Mustang Boss 302 #1918, Competition Orange. FGF replacement 2006 Mustang V6 Pony, Vista Blue. Factory ordered. 2019 BMW X3 (Titled to the wife, but I'm always driving it for her. So I'm claiming it) Old projects, gone but not forgotten: 1967 FB 400, original CA car. After 22 years of work, trashed by the guy who was supposed to paint it. I had to sell it. 1980 Turbo Trans Am 1970 Mustang fastback, 351C 4Bbl, auto 1988 Mustang GT, 5 speed 1983 F-150 4x4, built 302 1994 Chevy K2500 HD 4x4, 454 TBI
It depends on the fuel pump used. If the pump was designed to use a return line it's probably a good idea to hook it up. You can go either way, replace the pump or replace the matching sender. I would do the pump. Easier to get to and it sounds like your sender is new.
The 400s had the return, and the a/c cars I believe because they had the bigger volume pumps. My 350 (non a/c car) didn't have one. Now that I'm running a 400 and a larger carb the stock 350 pump couldn't keep up.
The fuel line on my car is also capped off. The fuel pump has a second line for the return but this is capped off as well. I do use a vented cap as well...
Here is a dumb question. Given that the filler tube is so low on the car and using a vented cap, is it possible that fuel will drain out of the cap when going up a sharp incline?
If not then I am going to abandon the return, use a vented cap and note that if I move from this 350 to a 400 that I will need a bigger fuel pump.
The return line from the pump to the tank is a whole different issue from a vented tank. I'm curious though, was it an a/c car originally? 2 or 4 bbl? Just trying to figure out application for the return line.
Here is a dumb question. Given that the filler tube is so low on the car and using a vented cap, is it possible that fuel will drain out of the cap when going up a sharp incline?
If not then I am going to abandon the return, use a vented cap and note that if I move from this 350 to a 400 that I will need a bigger fuel pump.
It depends on the fuel pump used. If the pump was designed to use a return line it's probably a good idea to hook it up. You can go either way, replace the pump or replace the matching sender. I would do the pump. Easier to get to and it sounds like your sender is new.
The 400s had the return, and the a/c cars I believe because they had the bigger volume pumps. My 350 (non a/c car) didn't have one. Now that I'm running a 400 and a larger carb the stock 350 pump couldn't keep up.
my car was once a 350 car, now 400....no, return line, but vented cap...no problems for the pump to keep up in my car.
From what I've researched, the 350-400 2bbl engines with a/c had the return line, and the 350-400 4bbl engines had the return line regardless...just what I've found.
When I converted my 350 car to a 455 I found there was not very many hi performance fuel pumps that didn't have a return line. There were some but it just made more sense to have it then to not have it. I ended up putting one in for my car.
The return line from the pump to the tank is a whole different issue from a vented tank. I'm curious though, was it an a/c car originally? 2 or 4 bbl? Just trying to figure out application for the return line.
Bob- I don't understand the purpose of the return line. I mean, I get the part that fuel is returned to the tank. But why is it returned to the tank? Did the pump build up excess pressure which could damage a carb? Or blow out the pump? Vapor lock? Can you give me the two minute primer (pardon the pun) on the purpose of the return line.
I believe the bigger bore engines and 4bbls(not sure about the a/c cars) got a fuel pump with more volumne. Since they delivered more fuel to the carb inlet than was needed at times the excess fuel was returned to the tank via an internal bypass in the pump and the return line. I don't know anybody personally that it's happened to so maybe it's just an urban legend but...I've heard it said that if too much back pressure is created on the fuel pump diaphram(ie., capped of return line) and it ruptures, your crankcase can fill with gas which can create several other issues. None of them good. Under normal conditions one of the smaller pumps should deliver more than enough gas. I'm running an 840CFM qjet on a 400 and it would run out of gas at about the 1000ft mark. Just wasn't strong enough to pull it all the way from the tank and keep the carb full. Changed over to an electric and problem solved.
