No good reason NOT to run one, but they're not necessary on carbed setups with stock or street performance level mechanical fuel pumps. They keep fresh, cool fuel circulating through the systems, which is only ever a good thing. They will help alleviate vapor lock and other fuel heat related issues. But you need to size them properly for your setup. They cannot present a restriction to fuel flow. When I switched to a Walbro 255lph fuel injection pump to run with my carb, I was required to add a return line and the appropriate regulator. In my case it needed to be a regulator that can drop the high pressure of the EFI pump down to carb-safe levels. So my supply and return lines are the same size. If you run a return line in this setup and you can't get your fuel pressure low enough, it's a sure fire sign that you have a restriction in your return. On a carb setup with a mechanical pump, you can run a smaller return line since the amount of fuel to return is typically less. So a 3/8" feed line can utilize a 5/16" or even 1/4" return. The pros say not to use a typical dead-head style regulator to run a return line, you want to use one that is specifically designed to run a tank return. I've also heard of guys having success by just adding a tee in the fuel line and running it back to the tank. I don't think I'd do that in any sort of performance application though. Sounds like a recipe for fuel supply issues or cavitation. Anything that prevents the fuel from dead-heading at the regulator is a good thing.
A filter in the suction line to the pump should suffice for that. The secondary filter before the carb should be for fines that make it through, and to keep them out of the needle valve and jets.
If any of you guys know of any articles or threads about this topic please link them here. This thread may help other people down the road.
I have a 1988 E350 Ford ch***is motorhome that has a 460 in it. It has a carb on it factory, and had a factory electric pump. It also had a fuel return, it was a gizmo about the size of a fuel filter {which I thought it was} with screw on fittings on each end and one on the side about middle ways. It got to starving for fuel, so I went and tried to find a replacement, had to order it from Ford, nobody else had or could get it. Meanwhile, I blocked the return and ran it, no problem. When I got the new gizmo and put it on, it started starving again, turned out my pump was dying and not putting out enough pressure. New pump solved my problem, nothing was wrong with the old gizmo. All the gizmo is is a cylinder with a spring loaded plunger inside, when pressure gets to a certain point, it opens and returns fuel to the tank. I think it was about $85 at Ford 5 years ago.
How much pressure drop would occur (if any?) if using this Wix filter vs. no return line at all? Note: i'm not too concerned about fuel pressure as i'm getting anywhere between 3-5.75/6 lbs. according to gauge, it's a quadrajet, and i rarely rev above 3000 rpm. i might, however, be having issues such as percolation in hot summer traffic jams.....maybe...?
I have always ran a fuel return line. That helps keep cool fuel at the carb and return excess fuel to the tank. Just fun a 1/4 inch line from the fuel line to thank. It’s an easy job to do.
Self-centered, but well-meaning BUMP: How much pressure drop would occur (if any?) if using this Wix filter vs. no return line at all? Note: i'm not too concerned about fuel pressure as i'm getting anywhere between 3-5.75/6 lbs. according to gauge, it's a quadrajet, and i rarely rev above 3000 rpm. i might, however, be having issues such as percolation in hot summer traffic jams.....maybe...?
Unless you are running a high volume mechanical pump, I doubt that you need a return line. If you are running a high volume mechanical pump or an electric pump, a return line is required (to me but some will disagree I am sure). The advantage of a return line on a pump and a byp***ing regulator is that it keeps the pump running at a lower pressure all the time where as a typical dead head regulator after the pump with no return line keeps the pump at max pressure all the time. This adds heat to the fuel and wears the pump out quicker. Typically, I will run a supply line from the tank thru a 100 micron filter into the pump. Out of the pump, the fuel goes thru a 40 micron filter (carb application) to the byp***ing regulator. From the byp***ing regulator, run the supply line to the carb. Run the return line from the byp***ing regulator back to the tank. Pretty simple and keeps your pump alive longer.
"How much pressure drop would occur (if any?) if using this Wix filter vs. no return line at all?" With a properly operating pump, there will be no pressure loss. This is because the pump is designed to provide a significant excess of fuel at any power output of the engine, and the tiny orifice will drain away less than the excess fuel always provided. If you have a mostly clogged fuel filter however the flow will be lower, so the small return drain will cause the engine to starve for gas sooner than if it weren't there.
He made an interesting point that the usual place of vapour locking is inside the mechanical fuel pump. I can believe this since yesterday when fooling with the carb on my old pickup I was feeling up the pump to see if was leaking, and it was darn hot. If the byp*** type filter is between the fuel pump and tank, it won't help cool the pump since the return is before the pump.
I like the 3 port filter method, but I already have a Holley 12-803 regulator, can I use the extra port as a return?
^^No, that is not a return reg. You need one like Scotty has below And you need the type of reg that Scott has. Holley 12-804 has the inlet on the bottom and the two uppers are outlets to the carbs. Fuel pressure is 1-4 pounds on the 12-804.
Hi Scotty T, I know this is a really late response to this post. But, I was wondering what route you had taken with your fuel return line? If so, did you take any pictures? In addition, did you go with the Holley 12-804 regulator? The reason, I'm asking. I have a 32 Ford Roadster with a SBC mild crate power plant and trying to run the newer Stromberg Big 97s tri-power setup for my nostalgia agenda. The issue, I'm having, my carbs are over loading with allot of fuel during idling. A small amount after it stops. I can still see fuel seeping in the carbs . I'm utilizing a mechanical fuel pump and the Holley 12-804 regulator (PSI set at 2.5 lbs). I'm going to check the inlet valves to my carbs to ensure I don't have any foreign material that's keeping the balls from closing, but usually this issue is caused by high fuel pressure. After I read this article and couple other articles, I was thinking maybe I could run a return line (5/16") back to the fuel tank to help with this issue and a preventive measure from the fuel heating up as well. I'm just trying to reach out and see if I'm on the right path or not. Any guidance would be greatly appreciated. VR, Mel
On the return line, I would not use the original suction line at the tank for a return. Returning fuel to the bottom of the tank would stir up any sediment in the bottom of the tank and get ****ed up in the new fuel pickup. Always run the return line to the top of the tank.
On that note, I've read that ideally it should be placed the opposite side of the tank for similar reasons.
I should have been more specific in my earlier post regarding the size of the return line. I use in tank pumps in 3 of my current cars. The pumps are FI pumps that Tanks Inc sell, and they recommend the fuel line and return line be -6AN. If you are running a mechanical fuel pump or a filter with a return line the size of the return line probably doesn't matter.
I know this was long ago and I never reported back. First to answer a question on the pressure gauge… it was screwed into the front bowl fitting. Now.. engine ran like ****. Could not get out of its own way, 1/4 throttle at best. I s****ed it all and went back to a smaller fuel pump dead headed and never went back. The carb only lasted one more run attempt and I went back to the double feed with a vacuum secondary and continued to improve speed and set records.
Try a MicroGard 33041 - it is the O'Reilly house brand. https://www.oreillyauto.com/detail/c/microgard/microgard-fuel-filter/mgd0/33041?q=33041&pos=0 I did not call the store to confirm availability. Russ
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