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Old 10-03-2015, 10:04 AM   #1
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'79 E350 460 Class C fuel issue

Howdy! I have a '79 Class C with a 460. Has 46k original miles. Gas tanks are clean and it has a Carter elec fuel pump as well as the stock mechanical pump. Original Motorcraft Carb has been recently rebuilt and fuel lines replaced. Here is the issue: it hesitates and will stall out when accelerating from a dead stop, such as a stop sign. It does regardless if hot or cold outside and engine is warm or cold. I do not believe its vapor lock as it doesn't display the same symptoms and I know vapor lock! It also displayed similar symptoms prior to rebuilding the carb but it runs a lot smoother and not as much hesitation now. I believe that there is too much fuel pressure. I am going to test it with a gauge. When it does stall, there is a strong fuel smell and it will start back up after waiting about 20 minutes or so. I also don't think it is the ignition module but am going to replace it as preventative maintenance. Otherwise it starts right up on the first turn and runs like a smooth top. Assuming that I am right and there is too much fuel pressure, please give me your advice on:
1. What pressure regulator so you recommend that is quiet.
2. What PSi do you recommend
3. Where should I install it. The electric pump is on the inner rail near the tank.
4. Should I either remove the mechanical pump or bypass it? I don't think having both is necessary.
5. I believe that A return fuel line is necessary if I install a regulator but not sure.
6. Any other suggestions or thoughts in the matter are appreciated.
Thanks!
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Old 10-03-2015, 10:23 AM   #2
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Test the pressure at the carb, the mechanical pump may already be acting as a regulator for the electric pump.
Do you have the spec's for the electric pump pressure?
With the condition you're describing, I'd be paying very close attention to the, accelerator pump action , with the fuel smell and the stalling the pump action may be too much for the engine at idle.
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Old 10-03-2015, 10:37 AM   #3
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Quote:
Originally Posted by Inthe70s View Post
Howdy! I have a '79 Class C with a 460. Has 46k original miles. Gas tanks are clean and it has a Carter elec fuel pump as well as the stock mechanical pump. Original Motorcraft Carb has been recently rebuilt and fuel lines replaced. Here is the issue: it hesitates and will stall out when accelerating from a dead stop, such as a stop sign. It does regardless if hot or cold outside and engine is warm or cold. I do not believe its vapor lock as it doesn't display the same symptoms and I know vapor lock! It also displayed similar symptoms prior to rebuilding the carb but it runs a lot smoother and not as much hesitation now. I believe that there is too much fuel pressure. I am going to test it with a gauge. When it does stall, there is a strong fuel smell and it will start back up after waiting about 20 minutes or so. I also don't think it is the ignition module but am going to replace it as preventative maintenance. Otherwise it starts right up on the first turn and runs like a smooth top. Assuming that I am right and there is too much fuel pressure, please give me your advice on:
1. What pressure regulator so you recommend that is quiet.
2. What PSi do you recommend
3. Where should I install it. The electric pump is on the inner rail near the tank.
4. Should I either remove the mechanical pump or bypass it? I don't think having both is necessary.
5. I believe that A return fuel line is necessary if I install a regulator but not sure.
6. Any other suggestions or thoughts in the matter are appreciated.
Thanks!
My first guess is that the accelerator pump may still not be putting out enough when you press the gas pedal. There could still be some crud in the fuel passages. With the air cleaner off, move the throttle quickly from idle. You should get a good squirt of gas. If the squirt is weak, you may be able to move the accelerator pump linkage to increase it.

On the other hand, you are probably correct that you have excessive fuel pressure. The smell of gas and having to wait indicates flooding. I checked in my shop manual for a different car and year that uses the same carburetor, and it says fuel pressure should be 5.0 to 6.5 psig. If you can find a Ford shop manual, it may have a different number, but I bet it won't be enough different to mess up your diagnosis. Test it with the electric pump off (pull fuse or cut wire) and with it on.

In my hot rodding days, which predate your RV by a few years, some guys kept the mechanical fuel pump when they installed an electric one so the mechanical pump would control the fuel pressure. Some installed a switch for the electric fuel pump and only turned it on when the situation demanded it. I don't think you should need an electric pump if you have a good mechanical pump, but there may be something about your RV that made it necessary.

As for a regulator, it would be most effective if it was between the mechanical fuel pump and the carburetor. The ones I was familiar with did not require a return line. They simply throttle the fuel flow when the pressure got higher then their set point.
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Old 10-03-2015, 10:54 AM   #4
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I would check the float level also the reason it restarts is that the extra fuel evaporates and lets it start.
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Old 10-03-2015, 02:57 PM   #5
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Foam plastic floats can absorb enough gasoline over time to sink or at least float low enough to mess up your float level setting. If you have the original float(s) I suggest replacement. If nothing else remove the float and tie a thin string to the metal float level and lower it into a bowl full of gasoline and see how well it floats.

I learned about this problem about six months after I installed a factory rebuilt carburetor and had flooding problems. The incompetents hadn't replaced the float!

Steve


BTW it was a Ford engine (but not a 460)
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