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Old 06-14-2012, 05:29 AM
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Leaking carb and fuel pump return line

I'm finishing up my 1974 454 swap into my 87 K10, and am having some trouble with fuel literally spraying like a fountain out of the top of my carb when I crank the engine over. The carb is a later Quadrajet that came off of an 85 small block that I sent out a year ago to be tuned and modified to add a little performance.

I can send the carb back to the shop to have it looked at, but before I do that I want to make sure that a second modification, one to the fuel pump, is not causing this issue. I wasn't able to get the stock mechanical fuel pump to clear the frame rails, but I was told that a pump from an early 70's biscayne with a 454 would clear and work. It does fit, but it doesn't have a return line on it like my old one.

Is it possible that this pump without the return line is building enough pressure to overcome the float/needle and seat in my carb? Or is it more likely that the carb is just rebuilt improperly?

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Old 06-14-2012, 05:58 AM
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Quote:
Originally Posted by carlk4728
I'm finishing up my 1974 454 swap into my 87 K10, and am having some trouble with fuel literally spraying like a fountain out of the top of my carb when I crank the engine over. The carb is a later Quadrajet that came off of an 85 small block that I sent out a year ago to be tuned and modified to add a little performance.

I can send the carb back to the shop to have it looked at, but before I do that I want to make sure that a second modification, one to the fuel pump, is not causing this issue. I wasn't able to get the stock mechanical fuel pump to clear the frame rails, but I was told that a pump from an early 70's biscayne with a 454 would clear and work. It does fit, but it doesn't have a return line on it like my old one.

Is it possible that this pump without the return line is building enough pressure to overcome the float/needle and seat in my carb? Or is it more likely that the carb is just rebuilt improperly?
i can only let you know how an edelbrock 10 psi mechanical pump works on a Ford windsor 347. The pump is internally regulated and does not need a return line. If the pump was not internally limited it would over pressurize the carb and would need a return line. Over pressurizing of the carb will force fuel past the needle and flood out the top vent tubesof my Holley 650. I had to use an inline regulator anyway and reduce the pressure back to 5.5 psi to suit the Holley operating specs.
I installed a pressure gauge in the line just before the carb to monitor the fuel pressure.
Some of this may apply to your problem but you will need a diagram of your pump internals . Could be a combination of pump and carb.
Al
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Old 06-14-2012, 07:31 AM
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Quote:
Originally Posted by carlk4728
I'm finishing up my 1974 454 swap into my 87 K10, and am having some trouble with fuel literally spraying like a fountain out of the top of my carb when I crank the engine over. The carb is a later Quadrajet that came off of an 85 small block that I sent out a year ago to be tuned and modified to add a little performance.

I can send the carb back to the shop to have it looked at, but before I do that I want to make sure that a second modification, one to the fuel pump, is not causing this issue. I wasn't able to get the stock mechanical fuel pump to clear the frame rails, but I was told that a pump from an early 70's biscayne with a 454 would clear and work. It does fit, but it doesn't have a return line on it like my old one.

Is it possible that this pump without the return line is building enough pressure to overcome the float/needle and seat in my carb? Or is it more likely that the carb is just rebuilt improperly?
Unless the pump you just got is somehow defective, the pressure would not be enough to cause the needle and seat to be overpowered. But there could be pressure built up in the fuel tank if the system is unvented. You can try removing the gas cap and see if there's a difference, but I doubt that's it.

Likely, something has fouled the needle and seat: a string of teflon tape from the fuel line fitting or carb filter housing would be a prime suspect.

If you want to take the time to do it, disconnect the fuel line from the carb, set it aside. Install another fuel line fitting w/a short length of tubing connected to it (or a hose barb fitting) and see if the needle and seat are holding pressure by connecting the line to a fuel source held above the carb. This could be a mower gas can and a length of rubber fuel hose. Get the fuel flowing by siphon, connect the line to the carb and see if it still overflows.

Or take the top off and have a look-see. Or return it for them to deal w/it.
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Old 06-14-2012, 08:55 AM
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I have had the same problem last week. The quad was rebuilt and installed. Started the car and ran it for 1/2 hour with no problems. The next day, started the car, carb leaking from the top and down the sides. Obviously a needle and seat problem! What I did was remove the fuel line and blocked it. Then started the car on the gas remaining in the carb until it sputtered and died. Next I took compressed air and blew it into the carb inlet. Replaced the fuel line and started the car. No more problems since. This is a lot easier to do then removing the top of the carb and trying to reinstall it after you look inside the carb to see what is wrong. Just my two cents.
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Old 06-14-2012, 06:42 PM
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Hopefully what ever it was doesn't end up plugging a jet.
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Old 06-16-2012, 07:17 AM
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fuel pump

What is the name brand of your fuel pump that you are using? I looked at a pump from Advance auto called Airtex for a 1971 Biscayne. It put out 7.5 to 9 psi, could be a little high for your carburetor.
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