carb/fuel question
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From: Houston, Tx.
carb/fuel question
Well, I got all my carb stuff done today, and ran into a little problem, maybe someone could help me out... Ok, about this AFPR (adjustable Fuel Pressure regulator). Ok, I found all the hoses necessary for this. There is a metal Fuel feed line, a metal fuel return line, and this rubber vent hose line that is behind my headlights. So, I dont have alot of money, so how can I get this to work without an AFPR? Would it work if I feed the fuel feed line to the carb (already done), and then cap the fuel return line? If I cant do this, why wouldnt I be able to? Will the electric fuel pump give to much pressure to the carb? Or what will happen? Of course, I took my car for a test drive, and fuel started coming out of the fuel return line, after about a 1/2 mile. So I dont get this. Please help if you can. Thanks guys,
Jordan
Jordan
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Joined: Apr 2001
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From: USA
Car: yy wife, crazy.
Engine: 350, Vortecs, 650DP
Transmission: TH-350
Axle/Gears: 8.5", 3.42
OK... most carbs from the factory run off a mechanical fuel pump. The fuel pump is restricted enough so it doesn’t build up more than 9 psi (the most I’ve seen even in the aftermarket). That’s about all a carb needs to keep the float bowls full.
If you run too much pressure into the carb, the needle in the float valve won’t be able to close, and the float bowl will stay open. This will cause fuel to continuously flow directly into the engine, bypassing the control the jets are supposed to have. Anyone who’s owned a Holley carb knows what that’s like.
The electric fuel pump in your car (regardless of whether your car was TBI or TPI) is designed to run at a much higher pressure than that. TBI’s run ~12 psi, where TPI’s run about 45 psi. The electric fuel pumps wouldn’t hold up well if they were constantly under a load and were required to keep the pressure at 45 psi. That’s why the return line is there.
The return line allows the pump to flow continuously regardless of pressure. The supply line runs to the pressure regulator where it “t”s off. One line goes to the injectors, while the other line goes back to the tank. Any pressure higher than the desired amount is what is sent back to the tank. This keeps the load off the fuel pump, which is why they last longer than if there were no return line.
What you’ve done is set the pump up to provide as much pressure as it possibly can to the float bowl. I’m surprised the float is able to close the valve at all. Even if it is now, it won’t be able to do it for much longer.
The return line you didn’t hook to anything is probably leaking gas that was either already in it, or the fuel in the tank is sloshing enough to be drawn into the line and forced out from the inherent pressure in the tank.
You need to do it right. Get a three port regulator and run the return line back to the tank. Set the pressure (with a gauge) between 5 and 7 psi. and all will be good.
The fuel pump will last longer, and you won’t be a flammable hazard to yourself or others (i.e., you won't be a "flammer"). :sillylol:
If you run too much pressure into the carb, the needle in the float valve won’t be able to close, and the float bowl will stay open. This will cause fuel to continuously flow directly into the engine, bypassing the control the jets are supposed to have. Anyone who’s owned a Holley carb knows what that’s like.
The electric fuel pump in your car (regardless of whether your car was TBI or TPI) is designed to run at a much higher pressure than that. TBI’s run ~12 psi, where TPI’s run about 45 psi. The electric fuel pumps wouldn’t hold up well if they were constantly under a load and were required to keep the pressure at 45 psi. That’s why the return line is there.
The return line allows the pump to flow continuously regardless of pressure. The supply line runs to the pressure regulator where it “t”s off. One line goes to the injectors, while the other line goes back to the tank. Any pressure higher than the desired amount is what is sent back to the tank. This keeps the load off the fuel pump, which is why they last longer than if there were no return line.
What you’ve done is set the pump up to provide as much pressure as it possibly can to the float bowl. I’m surprised the float is able to close the valve at all. Even if it is now, it won’t be able to do it for much longer.
The return line you didn’t hook to anything is probably leaking gas that was either already in it, or the fuel in the tank is sloshing enough to be drawn into the line and forced out from the inherent pressure in the tank.
You need to do it right. Get a three port regulator and run the return line back to the tank. Set the pressure (with a gauge) between 5 and 7 psi. and all will be good.
The fuel pump will last longer, and you won’t be a flammable hazard to yourself or others (i.e., you won't be a "flammer"). :sillylol: Last edited by AJ_92RS; May 7, 2003 at 10:42 PM.
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