FAQ – Carbureted Regulators

I want to convert my EFI engine to carburetion, how can I “knock the pressure down” coming out of my EFI pump? Does Aeromotive have a regulator for this application?

The greatest misunderstanding about fuel pumps is that they “put out” pressure. It’s best to think of the pump as a source of flow-volume. A bypass regulator creates pressure by restricting the volume flowing from the pump, thereby driving the pressure up to the set point. Once the pump has created enough pressure to open the regulator bypass, the regulator leaks just enough flow to maintain the desired pressure. The Aeromotive 13204 bypass regulator can flow enough volume on the return to handle most medium to larger EFI pumps, if the return line itself is large enough. Note: Most stock EFI return lines are too small for a carburetor conversion, creating more backpressure than the regulator. At minimum, carb conversions with a 13204 regulator will require a –6 AN return line for small OE pumps and a –8 AN for medium to larger pumps. Contrary to some conventional beliefs, the return line can never be too big if the regulator is right for the job. When in doubt, the bigger, more free flowing return line is the better choice.

I’m using a bypass style regulator for my carbureted fuel system. I want to install a nitrous kit. How do I set up a second regulator, either static or bypass, to control nitrous fuel pressure?
To avoid engine damage, be VERY careful with this one! Adding a second bypass regulator and attempting to set it for a lower pressure than the primary regulator, would default the entire fuel system to the lower pressure, creating a potential lean-out condition. Connecting a static regulator to a typical bypass system, with no more than 7-8 psi available, creates insufficient inlet pressure to the static regulator (12-15 psi is normally recommended). The result is reduced fuel flow through the static regulator and/or poor pressure regulation to the nitrous fuel solenoid, another potential lean-out condition. Short of installing a separate fuel system for the nitrous (highly recommended), the only option is to raise the bypass regulator set-point to 15-25 PSI, creating enough line pressure to feed two static regulators, each set for the proper carb and nitrous fuel pressures desired.

No matter where I set the adjusting stud, I can’t seem to change the fuel pressure with my standard (non-bypass) carburetor regulator, why?
Most standard carburetor regulators, including Aeromotive’, require some flow through the unit while pressure is being adjusted. the proper method is to set pressure with the pump on and the engine running. Correct procedure for a new regulator installation includes: 1) Turn the adjustment screw counter clockwise to the lowest pressure setting. 2.) Power and run the pump, with the engine off, until the bowls are full. 3.) Turn the pump off. 4.) Start the engine. 5.) Turn the pump back on. 6.) Adjust base fuel pressure up to the desired set-point by turning the set screw clockwise and locking the jam nut.

My regulator doesn’t seem to keep consistent pressure, every time I look at the gauge it reads something different, what is going on?
Chances are good you have a liquid filled fuel pressure gauge. This type of gauge will change it’s reading as the temperature of the gauge case changes. Because it’s sealed to contain the liquid inside, a liquid filled gauge no longer compares fuel line pressure to actual atmospheric pressure, reporting the difference. Instead, it compares fuel line pressure to the pressure inside the gauge case. Unfortunately, as the liquid in the case heats or cools, it expands and contracts, causing case pressure to change as much as 7 psi plus or minus. As a result, gauge readings can fluctuate from 8 psi cold to as little as 1 psi hot! Note: Fuel line pressure is NOT actually changing, just the pressure in the gauge case. To confirm if this is occurring, procure a heat gun or blow dryer and heat the gauge from cold to warm and then hot, while running the fuel pump. Observe if the pressure reading drops, if so, you found the problem.