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1979 F250 Custom Explorer 2wd 460 C6, 1984 E350 Type II Ambulance 460 C6
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Discussion Starter #1 (Edited)
Hi all, this is my first post here, but I'll leave the introductions for later. I just purchased a 1984 E350 Type II Ambulance (carbed 460) with supposedly a bad fuel pump in the rear tank and a hole in the front tank. I removed the fuel inlet line from the regulator/return valve/whatever you want to call it on the carb and attached a 7psi pump to a boat gas tank just to get it home. I disconnected the inertia switch and the fuel pump relay, but I still get fuel coming out of the inlet hose when it is running. The fuel tank is not full by any means. The only fuel that was in that tank came from what I have put through the return line. Anyone have any idea what I'm missing in stopping the fuel flow short of physically plugging the inlet hose? The return line still plumbed to the fuel tank, but I will be adding a fitting to the boat tank that I can attach the return line to and use it as a standalone system. Unfortunately it's my only running vehicle at the moment so I actually do have to drive it like this to get to work until I can get the tanks drained, dropped, and make my necessary repairs to the factory fuel system. I am concerned about spewing gas all over the ground while I'm driving, and possible fires which could start because of it. As a note, this is my first time working on a return style fuel system on a carbed engine, so I'm sure whatever I'm missing is completely obvious, but I just have no idea what it could be. Thanks in advance,
-Red
 

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Welcome to the FFO!

The return line is needed to prevent vapor lock during times of high heat. This combination had issues with that because of the lack of air flow around the engine and carb.

I am unclear as to what you have done or are doing.
Disconnecting the inertia switch and fuel pump relay stop the in tank pumps from working

You state you are getting fuel coming out of the inlet hose. The inlet hose to which part?

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1979 F250 Custom Explorer 2wd 460 C6, 1984 E350 Type II Ambulance 460 C6
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Discussion Starter #3 (Edited)
Welcome to the FFO!

The return line is needed to prevent vapor lock during times of high heat. This combination had issues with that because of the lack of air flow around the engine and carb.

I am unclear as to what you have done or are doing.
Disconnecting the inertia switch and fuel pump relay stop the in tank pumps from working

You state you are getting fuel coming out of the inlet hose. The inlet hose to which part?

Action
I have disconnected the inlet/feed hose from the tank selector valve to the carburetor and installed a boat tank with a fuel pump to run it temporarily without the use of the van's fuel tanks as one has a bad fuel pump and the other has a hole in it. The inertia switch and fuel pump relay were disconnected because I did not want fuel to flow from the tanks since the line to the carb from the tanks is disconnected, but the return line still runs to the tanks. The issue I'm having is I still have fuel coming out of the disconnected hose even though I have the fuel pump circuits disconnected and a relatively empty fuel tank.
-Red
 

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Plug the line.
And loosen up the fuel filler caps to vent.
With the fuel filler cap on, it is possible to build up pressure in the tanks
The amount & pressure of fuel coming though the fuel line to the carb is not great. Just securely plug off that line.

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1979 F250 Custom Explorer 2wd 460 C6, 1984 E350 Type II Ambulance 460 C6
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Discussion Starter #6
Plug the line.
And loosen up the fuel filler caps to vent.
With the fuel filler cap on, it is possible to build up pressure in the tanks
The amount & pressure of fuel coming though the fuel line to the carb is not great. Just securely plug off that line.

Action
Thank you very much! I figured it was something very simple. I'll find something to get that line plugged.
-Red
 

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1979 F250 Custom Explorer 2wd 460 C6, 1984 E350 Type II Ambulance 460 C6
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Discussion Starter #9
Yes It did
It worked when I posted it
Odd, but that's alright. Mr. Action's suggestion worked perfect to get me home leak free. It's now fixed up and running on the front tank with a parts store inline pump for temporary purposes until I can figure out why I'm getting no power to the fuel pump relay nor the inertia switch.
-Red
 

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These units were notorious for 2 things..(1) vapor locking, (2) catching fire. When we ran the gas units during the summer, we had to run them with 3/4 tank of fuel, and the fuel caps loose to keep them from vapor locking and/or pushing hot fuel out of the tanks. A mechanic came up with a way to get rid of the factory, in tank fuel pumps and wired up an electric pump mounted on the frame rails. He did this to 5 or 6 of the gas units, and believe it or not, they ran a helluva lot better and didn't vapor lock.....even with full tanks, and 100 F days. Mind you, I have no idea how he did it, I was a medic at the time, not a mechanic, but might be something worth looking into if you can find any info on these old units.
 

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The vapor lock issue was the reason for going to a bigger pump and using a return line. Carbed engines in vans or mostly motor homes (Class A and Class C) with the regular pump and no return line struggled in hot weather. More fuel moving and moving more fuel than needed is the answer. This was the reason for the return line. As long as the fuel was moving fast it had less time to pick up heat. Fuel that returned to the tank cooled down as well before being sent upfront again.

The engine fires were mostly due to the fuel filter that screwed into the Autolite 4300 A or 4300D (or later 4350) carb inlet. If not focused the filter would be cross threaded and cause a leak. If not when the initial cross thread, at least on the next installation. Usually the first time the tech would tighten (or over tighten) so the filter sealed. But the next guy doing it would almost never get a good seal. Then the carb or carb top had to be replaced depending on the model.

Pictured is a 1968 4300A First year. Contrast that to the 1975 4350 below. Nearly identical in design. The CFM is 441 or 600 versus the later 715 CFM for the late 4300 and 4350

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Autolite_4300A_Carburator.jpg
 
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Here is a 4350 spread bore

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4350.jpg
 
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