Updated October 2022 by Jerry Hoffmann
Carb-To-EFI Conversion: How to modify a carbureted fuel tank for EFI use
So you’re converting a factory carb’d car or truck over to EFI and you’re figuring out what to do about the fuel tank to prepare it for EFI use. In many cases, there are aftermarket fuel tank options that are designed for EFI from the start, you could simply buy one of these fitted with an in-tank pump, and check this item off your list! I other cases there may not be such an off-the-shelf solution available, or the budget may lead you to improvise, so you may have to figure out a solution yourself, either to build your own EFI tank from scratch, or to convert/modify your existing fuel tank for EFI usage. This appendix/article discusses the latter– how to modify a stock fuel tank originally intended for use with a carburetor, over to be used with a return style EFI fuel system.
First off in this article, we’ll look at how to physically modify your fuel tank. That’s where most of our time will be spent here. Then, after that, at the bottom of this page– we’re share a little cheat code with you that will work for some of you, particularly if you have a rubber section in your fuel tank’s fill neck that long enough for this little cheat.
First up– how to modify your factory fuel tank to add a return line
It’s not complicated and just requires tools you surely already have. A drill, a wrench or two, a screwdriver. That’s about it. And the parts you’ll need you can find at any decent hardware store.
Here’s a pictorial ‘how to’ of the process we used on one car we converted to EFI some number of years ago. It was a budget project done in a very DIY manner. And it has served us well on this car. This car, a Chevy Nova with SBC 350, was not aiming to make gobs of power. But to make a little more power, with better fuel mileage and excellent manners and drivability. The stock fuel line was plenty big enough for the power goals in this case, but there was no provision for a return line. We added one.
The fuel pickup/sending unit lid had plenty of room in our case. We didn’t even have to be too concerned with the size of the fitting we were using being particularly small. If it were too small, some careful cleanup of this assembly to remove all traces of gasoline could have made it safe to weld a return line tube or barbed fitting onto. We opted to use a DIY bolt-in method.
Essentially we just drilled a hole in the cap, and bolted in a bulkhead-style 90degree fitting with a barbed connection we could use with rubber, or steel braided rubber, fuel line for the return. Sized appropriately for the line we would be using on the return.
And well, they say a picture can say a thousand words. There’s 10 of em. That ought to be enough I think to give you the idea. It’s a simple project most anyone can do, but feel free to hit us up if you have questions!
Now for the cheat code…. the fuel tank filler neck return line option
And now, a picture (or two) that are worth another thousand words or so. If the goal of the return line is to get the fuel back into your tank, as simply as possible. Might there be another way?
Do you have a section of rubber tubing in your fuel tank’s filler neck? Is there room to replace a short section of that with a aluminum or steel section that has a return line fitting build right into it? Or, does your factory filler neck have a removable metal section you could remove, clean, and weld a return line into?
Pretty simple– as the fuel filler neck goes from the fill opening, to the tank– a return line placed in the middle does the job nicely! And it’s EASY!
Cheat code activated. This is a super easy option for adding a return line to your factory carb’d car’s fuel system!
Warning that should probably go without saying– You’re working around gasoline here. DON’T BE STUPID!!! Don’t be welding, or grinding around gasoline or gasoline fumes or you go boom!
That should go for pretty much everything you read on this site though, so…. I digress….
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