riplt1

i'm putting together my first carb setup. i know to run the feed line to the pressure regulator and then to the carb. but i don't know where to hook the return line up to.

i'm running a standard holley pressure regulator. p/n #12-803. it has three ports. two are stamped, "out" and one is stamped, "in". The instructions say to run the feed line to the "in" port. And run the out ports to each carb if you're running a dual carbs. and if you are running one carb to plug the extra "out" port.

i want to know where if i plug the extra port, where do i run the return line to?

69RS

iTrader: (1)

That is a dead head psi regulator, there is no return line. If your running a Holley blue pump, none is required. Just put a gauge in line or in the spare port so you can set the psi. 6.5 should do the trick.

cambirdracing

iTrader: (4)

X2...

riplt1

i'm running a holley proform 750.

so i don't have to hook the return line up to anything?

bb5401000

iTrader: (2)

There is no return line. You can hook each out port individually to a separate inlet fitting on the carb, one to the front and one to the rear. This is the best way to hook it up.

1 FMF

iTrader: (1)

what you can also do is run fuel line from the 2nd port to a fuel gauge either mounted or hand held in the car. usually you would just have the gauge near the regulator when idling to set the regulator, but ideally you would want to know what fuel pressure is under high demand (wide open throttle and high rpms). you can do this easily since it's a two port reg, and could even mount a fuel pressure gauge inside if you wanted to. under demand it is not uncommon for fuel pressure to drop as low as 1-2psi, and knowing how low it drops will help you in knowing how high to set the regulator pressure to begin with or if you need a better fuel pump, or have a problem elsewhere.

riplt1

ok. i'm going to run one line to the carb and a line with a pressure gauge inside the car.

but what i still don't understand is where the excess fuel thats not being used go? if the regulator is pushing out a constant pressure of say 6 psi, its not using all that at idle so where does it go?

riplt1

i also don't think my pump will shut off. i'm running an areomotive ss carb pump.

http://aeromotiveinc.com/products-pa...l-pump-38-npt/

1 FMF

iTrader: (1)

it depends where in the circuit the pressure regulator is whether it needs a return to bleed off pressure or not. For fuel injection, which has a fuel injector rail, needs a constant pressure rather than a maximum pressure. The regulator is off the fuel rail and is spring loaded, fuel pressure pushes into it. If pressure is not great enough, the regulator does not open, but when pressure exceeds the spring pressure in the reg it opens allowing the excess fuel to flow out of the injector rail, maintaining a constant rail pressure. This extra fuel, from bleeding off the pressure to maintain a constant pressure, has to go somewhere so there's a return fuel line to the fuel tank.

For carbs, that is a dead end fuel circuit. There's no need to maintain a constant pressure, and it's the job of the needle and float in the carb to maintain a constant fuel level in the bowl. All a carb needs is fuel pressure to be below some max so pressure doesn't overwhelm the needle and float and fload the carb. Fuel pressure regs for this setup have no return of excess fuel port, it's still a spring loaded reg with a little door flappy thing in it, they work the same way a water pressure reg does for your house if you have one which internally is backwards of the fuel injection pressure reg with a return. These operate in a manner where fuel pressure equals the spring pressure of the regulator, the regulator stops flowing, which maintains a maximum preset pressure on the output side going to the carb. And you could use this for fuel injection but you need to have it prior to the fuel rail. The fuel pump in either case doesn't care, it just pumps away and doesn't care what pressure it outputs.

riplt1

thanks for the help guys. i got it all hooked up and going well. i'm running 7 psi

cambirdracing

iTrader: (4)

I would not keep the gauge inside the car. First it's not safe unless you use an isolator and second, if you go to the track, it is against the rules, unless you have an isolator.

http://www.jegs.com/i/Auto+Meter/105/2413/10002/-1