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Fuel return line

Dpbeats11

Dpbeats11

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Going to be installing a fuel return line going into fuel sending unit coming from fuel filter by carb. Would this take away from the fuel going into the carb and send it back to the tank instead of the carb? Only using a mechanic fuel pump at the moment. Currently the fuel filter won’t stay full once I drive around the block a couple times. Almost seems like the pump can’t send the fuel through the lines fast enough. But then again it seems like vapor lock. After a fast run around the block, the fuel filter is only half full causing car to shut off during deceleration. At this point can’t determine if the problem is vapor lock or fuel pump issue. Willing to try anything to keep fuel in carb and not have it shut down on me.
Thanks
 
Probably going to need to know engine size/ hp levels, type of driving, current fuel line size , current fuel pump and the pressure it's running, carb size. It could be one or the other or something simple like float level or partly clogged pick up sock. Lots of extremely knowable guys on here to help if they have that info or most of it.
 
If a big block it could also have a worn fuel pump push rod. I would start with the simple stuff first as mentioned above.
 
Is the filter installed such that all air can escape?
If the filter is only half full, how does the engine run at all?
 
I doubt that's why the car is shutting off. Fuel filters rarely get rid of the air bubble inside of them. Nobody realizes this until they run a clear plastic one... that shouldn't be under your hood anyhow. Put a metal one on the air bubble will "go away". Car shutting off is something else. Carb isn't asking for fuel on deceleration !
 
In addition to what the other guys suggest, check for a fuel line leak ahead of the fuel pump. Such a leak may allow air to be sucked in through the leak. It may not leak fuel if the leak is above the level of fuel in the fuel tank.
 
Dan64 said:
Probably going to need to know engine size/ hp levels, type of driving, current fuel line size , current fuel pump and the pressure it's running, carb size. It could be one or the other or something simple like float level or partly clogged pick up sock. Lots of extremely knowable guys on here to help if they have that info or most of it.
Click to expand...

To add, engine is a 318 with 2 bbl carter carb. I couldn’t say what HP would be at the moment. Driving is mainly city. Have 5/16 lines to fuel pump then up to fuel filter then going to carb. Fuel pump is a carter mechanical. I would assume fuel pressure is around 6psi.
 
dadsbee said:
I doubt that's why the car is shutting off. Fuel filters rarely get rid of the air bubble inside of them. Nobody realizes this until they run a clear plastic one... that shouldn't be under your hood anyhow. Put a metal one on the air bubble will "go away". Car shutting off is something else. Carb isn't asking for fuel on deceleration !
Click to expand...

i currently have a glass filter between fuel pump and carb which is how I notice the level inside. Occasional when it gets warm I do see bubbles start to form. Afraid when I installed metal fuel filter with return line I won’t know how full the filter is getting.
 
Stanton said:
Is the filter installed such that all air can escape?
If the filter is only half full, how does the engine run at all?
Click to expand...

Currently the filter is installed horizontally, only notice the half filled filter after I run it hard and let it sit idle for a minute. Seems like it has hard time filling back up. Here is a pic of where the filter is located. Obviously this engine has seen better days. Slowly trying to clean it up.
85DE5693-A0FD-4E88-BB34-437915A86EF3.jpeg
 
You have a 318 2bbl, you don’t need a return line. Your problem will still be there. You need to focus to find the problem with your carb or fuel supply. The Fuel filters always have air in them, just cannot see through a metal one. That’s not the problem. All of our cars are dong that even when they run good.

And don’t be afraid, you’ll never get anywhere like that.

Take the gas line off at that filter and run into a container, have a helper start the car and see how much fuel is pumping out. Factory service manual says 1 quart in 1 minute or less @500 RPM. That will check the supply.
 
Last edited:
There is a few way to run the return line. Using a by-pass style pressure regulator provides fuel to the carb as needed, and bypasses the rest. In low demand cases most of the fuel is bypassed. Think of the regulator as a variable sized restriction.
The second is simply a restriction in the return line, so a small amount of fuel is always returned, but allows any air/vapor to pass through the return.
I don't know what the optimal restriction size would be as it depends on how much extra fuel the pump provides that the engine does not need.
I might start with a 0.040" return restriction, then monitor fuel pressure at the carb to see if it falls off at high load demand.
 
Dan64 said:
Probably going to need to know engine size/ hp levels, type of driving, current fuel line size , current fuel pump and the pressure it's running, carb size. It could be one or the other or something simple like float level or partly clogged pick up sock. Lots of extremely knowable guys on here to help if they have that info or most of it.
Click to expand...

checked float, measured at 1/4 inch. Question about plunger, how much resistance should there be with the plunger moving up and down?
 
R413 said:
You have a 318 2bbl, you don’t need a return line. Your problem will still be there. You need to focus to find the problem with your carb or fuel supply. The Fuel filters always have air in them, just cannot see through a metal one. That’s not the problem. All of our cars are dong that even when they run good.

And don’t be afraid, you’ll never get anywhere like that.

Take the gas line off at that filter and run into a container, have a helper start the car and see how much fuel is pumping out. Factory service manual says 1 quart in 1 minute or less @500 RPM. That will check the supply.
Click to expand...

will be checking fuel supply today. Another question, what would cause filter to be full at start up and idle until warm, then after driving the filter has trouble staying full. The reason I suspected vapor lock, the hard fuel line going to fuel pump is about 6 inches or so away from the headers. I guess I’ll have an answer after checking supply
 
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