Whats inside the gas tank? At evap barb.
You can NOT use that line for fuel return (or shouldn't) for a couple of reasons
First, originally, that line IS the tank vent. It went up front as you know, tied in with the evap/ carbon can system, and vented the tank. THERE IS NO OTHER vent
Also, did your car originally have the "big can" (vapor separator) in the trunk? It should not have had, unless it was an earlier model. Earlier evap systems had that, with 3? or 4? vent lines from the tank, later ones had only one 1/4" fitting at the tank
Look up a 69 service manual (free) from MyMopar and you will quickly see how the "un" evap tanks vented----using a simple tube welded into the upper filler neck
(While you are at it get a 73 manual from there too. Read the fuel and emissions sections to find out how this all worked)
Second, that line is likely WAY too small if you are talking about a return regulator/ EFI/ etc. If you are simply talking about a fuel/ vapor return from something like a 3rd port fuel filter with the anti-vapor lock orifice, then it will be ok, BUT YOU STILL would need to provide a vent
The fuel caps in none of these cars are vented--and that fact helps keep fuel off the fenders
If you don't provide another vent, that fitting needs to remain "up front" and "up high" to prevent siphon.
This is 70 / without evap and 69/earlier tank vent
You can NOT use that line for fuel return (or shouldn't) for a couple of reasons
First, originally, that line IS the tank vent. It went up front as you know, tied in with the evap/ carbon can system, and vented the tank. THERE IS NO OTHER vent
Also, did your car originally have the "big can" (vapor separator) in the trunk? It should not have had, unless it was an earlier model. Earlier evap systems had that, with 3? or 4? vent lines from the tank, later ones had only one 1/4" fitting at the tank
Look up a 69 service manual (free) from MyMopar and you will quickly see how the "un" evap tanks vented----using a simple tube welded into the upper filler neck
(While you are at it get a 73 manual from there too. Read the fuel and emissions sections to find out how this all worked)
Second, that line is likely WAY too small if you are talking about a return regulator/ EFI/ etc. If you are simply talking about a fuel/ vapor return from something like a 3rd port fuel filter with the anti-vapor lock orifice, then it will be ok, BUT YOU STILL would need to provide a vent
The fuel caps in none of these cars are vented--and that fact helps keep fuel off the fenders
If you don't provide another vent, that fitting needs to remain "up front" and "up high" to prevent siphon.
This is 70 / without evap and 69/earlier tank vent