I have been chasing an issue (vapor lock, fuel pressure dropping with heat) with my fuel system for a few years, and I know there are others out there who encountered the same issue, so hopefully this information will help the community avoid all the mistakes I made on the way to figuring out a solid carburetor fuel system.

Due to the fuel lines on the original carbed motors running right next to the exhaust, many of us encounter vapor lock in stock configuration. Add in headers, aftermarket carbs, or entirely different power plants and the stock fuel line routing becomes almost unusable. However there is not a really good alternative routing that I have found that uses factory style hard lines and is easy to install without a lift. Here is what can be done to prevent vapor lock and provide fuel at the proper pressure to an aftermarket engine/carb setup that requires substantially more fuel than the stock motor and is easy to install, clean looking, and effective without being expensive.

I have had a GMPP ZZ4 with an Edelbrock 1806 carb in the car for years, an engine that does not come with any provision for using a mechanical fuel pump as most hydraulic roller camshaft engines don't. When I installed the engine, I just tossed a holly red pump right at the fuel line head where it once ran to the mechanical fuel pump. This worked terribly, as I now understand almost all electric fuel pumps are designed to push fuel, not suck or pull fuel the entire length of the car. Additionally, the pump would get exceptionally hot as it was sitting next to the header (go figure). After going through three of these pumps, under warranty fortunately, I switched the mounting location to the rear of the car, right in line between the tank and the hard line. The pump lasted longer there, but I still would have vapor lock on hot days or after driving for extended times.

I figured that using the return line would help cool the fuel, so I dropped in a standard holley regulator (P/N 12-803) and mounted it up near the carb, so that fuel would go into the regulator and out to both the carb and return line. That meant I had two fuel lines running up to the engine, generally cluttering up the look of the motor. This worked, but my fuel pressure never got above 4 PSI, and would drop to 2 PSI under hard acceleration, causing the engine to run dangerously lean. I tried to correct this by going with a better pump, a Carter black 4601HP, but still would lean out crazily and the condition got worse the longer the drive. This fuel pump is rugged and quieter than the Holley pump was, and has been in the car problem free for 9 years. I did have issues with the holley pump getting wet and the leads coming loose, but the Carter pump is rated for Marine service and has better electrical connections to prevent them from vibrating off.

Finally I got fed up with the whole system and did substantially more research, coming to that "Aha!" moment that I probably should have had years ago. The Holley regulators are almost all exclusively for use in a non-return style system. The two outlet ports on their regulators are for dual feed carbs or for running a fuel pressure gauge on one side. If used in a return style system, they basically free flow fuel back to the tank, which is great for cooling but not great for feeding the carb. I had no vapor lock issues at this point as the fuel was staying cool enough, but I would run in to over-pressurizing the fuel tank and having the fuel cap almost pop off when it came time to put gas in the tank. I needed a return style regulator built for a carb application, and I needed a better plumbing solution.

The regulator I went with was a QuickFuel 30-900, which is factory preset to 6.5 PSI outlet pressure and will send any surplus fuel pressure to the fuel tank via the return line. This exact one had a vacuum line provision, which may come in handy for some applications where more fuel pressure is needed at WOT. I don't really have that issue with the carter pump as it can move sufficient fuel at decent pressure to keep the carb fed at 6 PSI at WOT. Holley has the 12-803BP that more or less does the same thing, except it's not red. I like red, and the QuickFuel was $10 cheaper at Napa.

For plumbing, I ordered up a 6AN fuel line kit from Amazon for just under $50. This kit came with 10' of line and an assortment of AN connectors, enough to run to the regulator from hard line, up to the carb, and to the return line. I also used the Edelbrock 8131 fuel line kit with filter, another $40, but not necessary if you want to run the line directly to the fuel inlet on the carb. I also needed three 6AN to 3/8" NPT connectors for the regulator, and hard line adapters for both the 3/8" hard line and 5/16" return line. A handy addition is the 3/8" NPT to 6 AN coupler that has a 1/8" NPT port for a fuel gauge. This can take the place of the regular adapter on the outlet to the carb.

I mounted the regulator using the hole I had drilled for the holley fuel pump, right on the strut tower. It kept my line lengths minimal and everything is tucked away nicely. Now only one fuel line goes over to the carb, and I have a nice cool fuel supply. I used some cheap aluminum sheeting to wrap the whole thing from fuel hard lines to the side of the regulator to shield it from the header.

Now fuel stays at that 6.5 PSI range (the gauge always shows 1 PSI, I should have replaced it too) and the fuel stays cold. After a long test drive of a tank and a half of gas, no vapor lock and my fuel pressure as well as Air/Fuel ratio stays right where I want it regardless of driving conditions. I still had a slight pressure issue with the fuel tank, but a vented cap solved that problem. I highly recommend having a wide band oxygen sensor and A/F ratio gauge, as this is the carb tuner's best friend when finding and correcting fuel system issues. Without this I probably would never have known how lean I was running until the engine blew up or overheated.

Piecing together the hose fittings is fairly straight forward, but make sure that you have a good vice with brass jaw plates, Teflon tape or fuel tape, aluminum adjustable wrenches (if you don't want the anodizing on the fittings messed up, regular wrenches work fine too), a pipe cutter (low profile works best) and most importantly a PVC style hose/pipe cutter. This cleanly cuts the fuel line for the AN style fittings to attach to, especially if you use masking tape to cover where you cut it. Remember that the collar on the fuel line (the red part in this case) is left hand thread.

Complete parts list for an easier time shopping:

5/16" to 6AN coupler BAN108-5-bk ($10)
3/8" to 6AN coupler AN108-06 ($15)
3/8" NPT to 6AN with gauge port FP194-06-08 ($14)
Russel 3/8 NPT to 6AN coupler 660460 ($3 each, need at least 3 if not using the gauge port adapter)
6AN Evil Energy fuel line kit FBA-KT00398RK ($43)
EDL8131 fuel line kit with filter ($41)
QuickFuel bypass regulator 30-900 ($82)
Carter 4601HP fuel pump ($100)
Mr Gasket Fuel pressure gauge 1561 ($19)
Sheet of aluminum ($5 at local hardware store)

$335 total project cost, which is hard to beat considering that the Summit fuel pump kits don't have the right regulator or all the fittings needed and cost about $350. The car is running well, the system looks and works good, and I am not slapping my head in frustration. Well worth the time and effort, and I certainly hope this helps others dealing with fuel system problems like I was having.