Between the weather and a health scare, it’s been a while since I had much time to work on the Valiant.

Now that were back at it, we decided to get the fuel system sorted out. As I found out when sorting out the first car I built when I moved to Arizona in the mid-80s, vapor-lock can be a real issue on a carbureted daily driver where I live.

Besides the heat being the major cause for vapor-lock additional aggravating factors include altitude (I’m at 4500ft and often travel to higher elevations), and oxygenated (ethanol) fuel (E10 is the most common and available premium fuel in this area). Basically where I live I hit the trifecta for vapor lock.

After going thru a lot of the typical “fixes” for vapor-lock on that first Arizona build, I found the only real fix on a low pressure fuel system was to run a return line. This keeps the fuel moving thru the system and prevents the heat buildup that will cause the fuel to boil in the fuel line. With that in mind I started collecting the parts for the fuel system.

When I bought the new gas tank, I also orders a new sending unit to go along with it. There are currently be 2 sending units readily available for these cars. One for a 5/16” fuel line and the other for a 3/8 fuel line. I chose the 3/8” one in part because it has a nipple for fuel return line.


Sending unit by M Patterson, on Flickr


Next up was collecting the rest of the parts for the rest of the fuel system, and building what I needed to meter the fuel being returned to the tank. Before anybody comments about my fuel pump choice, I’ll be covering that in my next post.


Fuel system by M Patterson, on Flickr


When I finally installed the fuel return system on that car 35 years ago, I was using a fuel pressure regulator to control the amount of fuel bypassed back to the tank. Back then I had a heck of a time getting one that would work properly or last very long. I finally solved that problem by replacing the regulator with a fitting containing a fixed orifice.


Bypass by M Patterson, on Flickr



Somewhere along the line I figured out that a 1/4” NPT fitting/pipe is the correct ID to run an 1/8” NPT tap through. Then I use an 1/8 recessed pipe plug with a hole drilled in the center as the metering device. The hole size doesn’t appear to be very critical, I’ve used as large as an 1/8” hole and as small as 1/16” …..for this one I’m starting out with a 5/64th” hole .


Some may also note that the fitting on the return line I’m using a compression fitting rather than a flair fitting. Believe me normally I do not use compression fitting on anything automotive. In this case it was what I could find that would work……from a safety stand point it should do fine. Under normal conditions pressure in the return line will probably be under 1 PSI, in the worst case, (like the return line becoming blocked) the fuel pump I’m using has a max pressure of 6 PSI.


Personally I liked the cleaner look of the fuel line I originally built for the engine on the test stand.


Fuel Line 1 by M Patterson, on Flickr


The return system I built is definitely a case of function over form. I want the return to start as close to the carburetor as possible or in the case of multiple carbs at the furthest carb in the system.


Return line by M Patterson, on Flickr


Basically it is what it is. Given the choice of how it looks and nursing a vapor-locking car home, I can live with it .



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