FAQ - Carbureted Regulators
1. I want to convert my EFI engine to a carburetor, how can I “knock the pressure down” coming out of my EFI pump? What Aeromotive regulator should I use for this?
A common misconception about fuel pumps is that they “put out” a specific pressure. It makes more sense to think of the pump as a source of flow. A bypass regulator creates pressure by restricting flow from the pump, forcing the pump to produce pressure up to the regulator’s set point. Once enough pressure is created the regulator bypass is forced open, allowing excess flow onto the return line. From here the regulator relieves just enough excess volume to maintain pressure. The Aeromotive 13301 bypass regulator can bypass enough volume to handle most medium to larger in-tank 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 13301 regulator will require a –06 AN (3/8″) return for small OE pumps and an AN –08 (1/2″) for medium to larger pumps. When in doubt install the larger, freer flowing AN -08 line to ensure good results.
If the return line is too small, the question becomes, “Besides running a bigger return line, is there any other way to use the stock, in-tank EFI fuel pump to feed a carburetor?”
There is one possibility, but it means adding another regulator, using both a bypass and a static regulator together. In this case the 13301 regulator is used to first control what is called “line pressure”. This means feeding the stock supply line into the 13301 and then running the stock return line from the bypass port back to the tank. Next, the outlet line from the 13301 is fed into the 13205 static regulator before going to the carburetor. The 13301 is set for 12-14 PSI, high enough to allow use of the smaller, stock return line and then the 13205 is used to block that down to the 5-8 PSI range for the carburetor.
2. 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 bypass regulator will default the entire system to the lower pressure. Feeding a new static regulator from an existing bypass system, either before or after the bypass regulator, will not provide adequate inlet pressure to the static regulator. Understand, a dead-head regulator needs two times inlet to outlet pressure and a bypass regulator creates the same pressure at the inlet as it does the outlet. Running a static regulator for nitrous set at 5 PSI with only 7 PSI inlet pressure is a recipe for nitrous lean-out and potentially serious engine damage.
Short of installing a separate fuel system for the nitrous (highly recommended), the only reasonable option is to raise the bypass regulator pressure up to 15-25 PSI. This is enough line pressure to feed multiple static regulators, one for the carburetor and others for nitrous stages. Aeromotive now offers stackable, modular static regulators under P/N 13217that can be bolted together for easy installation and the regulator body forms its own fuel log. Using bypass regulator P/N 11217 attached to the last stackable regulator to create line pressure necessary to feed multiple carburetors and nitrous stages. This is perfect for nitrous using inline fuel pumps like the A1000, Eliminator and Pro-Series.
3. No matter where I set the adjusting stud on my static (non-bypass) regulator, I can’t seem to control the fuel pressure consistently, why?
Most static carburetor regulators, including Aeromotive’s, require some flow through the unit while pressure is being adjusted. The proper procedure is to turn the pump on, start the engine and then set pressure. Steps for installing and setting a new regulator include: 1) Turn the adjustment screw counter clockwise to the lowest possible 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. Note: If you go to up and want to come down, make a small adjustment, turning the adjusting stud counter-clockwise, and then blip the throttle a couple of times to bring the pressure down.
4. I’m using a static (non-bypass) regulator and every once in a while the pressure spikes, going past the set point and pegging the gauge, flooding the engine. What’s wrong?
This condition is called pressure creep. It’s caused by the regulator failing to seal and stop flow when the set pressure is achieved. A static (blocking) regulator must close and stop flow perfectly to control pressure. A dead-head style pump is designed to create pressure from 14-21 PSI, in the range of 2-3 times higher than the regulator set-point. Anything that prevents the regulator valve from closing and sealing will allow it to leak, causing pressure to creep up at the needle and seat, sinking the float and flooding the engine. When pressure creep is a problem it’s common to find debris has lodged in the regulator valve. The regulator may be able to be disassembled, cleaned and restored to proper operation. In the event cleaning does not resolve the problem a rebuild kit with replacement valve will normally fix it. Aeromotive offers rebuild kits with replacement valves for all Aeromotive static pressure regulators.
5. My regulator doesn’t seem to keep consistent pressure, every time I look at the gauge it reads something different, it’s driving me crazy, what is the problem?
Chances are good you have a liquid filled fuel pressure gauge, infamous for changing its reading with temperature. Because a liquid filled gauge is sealed to keep the liquid inside, the pressure inside the gauge case may not be equal to atmospheric pressure. Once sealed shut, the liquid in the case expands and contracts as gauge temperature changes, making the internal pressure in the gauge vary up and down as it heats and cools. Case pressure can change as much as 7 psi up and down with heat, which affects the gauge mechanism and changes the gauge reading by the same amount!
Note: Even though the needle is moving up and down, fuel line pressure is NOT actually changing, the pressure in the gauge case just makes it look like it is. Testing for this problem is easy, just carefully heat the gauge, using a heat gun or blow dryer, from cold to warm and then hot, while running the fuel pump. The gauge reading will drop as the oil inside warms up and the pressure in the gauge case increases. Now pop the plug in the side of the gauge case and watch the pressure come back up, reading the same as before the oil was hot.
Aeromotive now offers a brand new, state of the art, Liquid Filled Fuel Pressure Gauges for carbureted and EFI engines P/N’s 15632 and 15633 respectively. These new “equalizer” gauges feature a pressure equalizing pin-valve in the side of the case allowing the user to compensate for heat related changes in case pressure, quickly restoring gauge accuracy at any operating temperature.
For more detailed information on problems with liquid filled gauges, and the new “equalizer” gauges, see Aeromotive Tech Bulletin TB-903 at www.aeromotiveinc.com under the Tech Help, Tech Bulletin section.
6. What is the barb fitting in the regulator cap used for? How and where should it be connected if I use it, and what should be done with it if I don’t?
All Aeromotive, carburetor bypass regulators incorporate the necessary design to allow the regulated fuel pressure to be vacuum or boost referenced, on a 1:1 ratio. For “blow through carb”, forced induction applications, where a turbo or centrifugal supercharger pressurizes the carburetor through a hat or in an enclosure, the regulator boost port should reference to positive pressure only, not vacuum. connect the port to the carburetor box or hat, not the intake manifold. For carbureted, naturally aspirated engines, and for roots supercharged engines where the blower draws through the carburetor, the vacuum/boost reference port should be left open to atmosphere, never plugged.
There is one potential use for referencing fuel pressure to vacuum on a naturally aspirated (not blow through) carbureted engine; where alcohol is the fuel of choice. In this case a line from the regulator to the base of the carburetor, beneath the throttle blade into the intake plenum, can be used to lower idle fuel pressure and allow higher fuel pressure to feed the carburetor at wide-open-throttle.
For more detailed information on carburetion and vacuum/boost referencing fuel pressure, see Aeromotive Tech Bulletin TB-201 at www.aeromotiveinc.com under the Tech Help, Tech Bulletin section.
7. I have a dead-head (blocking) style regulator and I want to run a return line. Will it work if I connect a return line to one of the spare outlet ports on the regulator and run it back to the tank?
No, this will not work. An open return line from one of the regulator outlet ports will render the regulator unable to properly control pressure, resulting in no pressure at idle, or at best low or no pressure at WOT under high engine load. Static regulators are normally open and designed to close when the set pressure is achieved, bypass regulators work on the opposite principle.
Pressure to a carburetor normally builds when the bowls are full and the needle shuts against the seat. An open line from an outlet port on a static regulator, running back to the tank, will prevent pressure from ever building at the carburetor needle and seat to begin with. It would be the same as taking a line from the regulator and putting it into a bucket; turn the pump on and you’ll have plenty of flow out of the line, but little or no fuel pressure to register on the gauge.
The only way a return line may be connected to a static regulator is if it is through a port blocked by a highly restrictive jet, normally something with a passage in the 0.015″-0.017″ range. This is done to allow a small amount of fuel to leak through the regulator valve to prevent pressure creep on a nitrous solenoid.
There are excellent reasons to install a proper bypass regulator for use with carbureted engines and Aeromotive has perfected this technology, offering a variety of world class bypass regulator options.
For more information on Static vs Dynamic Fuel Systems and the benefits of a bypass regulator, see Aeromotive Tech Bulletin TB-801 at www.aeromotiveinc.com under the Tech Help, Tech Bulletin section.
8. I have one of your Carbureted bypass regulators, advertised to adjust from 3-14 PSI. I have a blow through carb and am setting the system up for boost reference with 7 PSI at idle and 20 PSI boost. Pressure needs to hit 27 PSI with boost reference, will it work or stop at 14 PSI?
It will work perfectly, raising fuel pressure with boost on a 1:1 ratio, all the way to 27 PSI, if the pump will support it. There’s no real limit to boost reference as far as the regulator is concerned, but it’s important to understand that as fuel pressure goes higher, the flow from an electric fuel pump trends lower, and when the pump flow is no longer sufficient to support the engine’s demand for fuel at the increased pressure, fuel pressure will flatten (stop rising) and then it will roll over and start to fall if fuel demand continues to rise. This is a pump/flow problem, not a regulator issue.
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