Fuel vaporization fix
First, the fuel cap should be a "pressure / vaccum" cap which does NOT mean that it is operationally vented for the engine. This means that if the tank develops excessive internal positive or vacuum pressure, the cap will RELIEVE.
The operational vent is done by the evap emission system, part of which is in the tank (this changes over the years 70-later) and the 1/4" tube which comes to the engine bay. THAT tube is not only part of the evap control system, and originally ties in with the engine bay "carbon can" stuff, but ALSO IS THE operational vent, allowing the tank to properly vent during driving
If you don't need nor want the evap controls, that 1/4 line MUST be up high in the engine bay--to prevent siphoning, and must be left open. You can plumb it into the open air side of the PCV AKA the vent line to the filter bonnet.
If you don't want to do that, figure a safe way to install a fitting up high in the filler neck and convert the vent to a 69/ earlier vehicle. Those used a completely sealed cap
I WOULD NOT RUN a vented cap because of the danger of dribbling fuel over the side when full, etc.
Below is the 69/ earlier style vent. Simple. BE CAREFUL when choosing/ replacing a cap. The caps changed almost every year. There is a "famous" photo posted on here by Steve, OldManMopar, that shows several caps from 70--to the end. They are DIFFERENT
https://www.forabodiesonly.com/mopar/threads/fuel-tank-vent.505304/
The secret of the simple old style vent is that the bend goes up high against the top of the quarter panel, and "breaks" any siphon. It simply goes down alongside the filler tube and punches through the floor gasket, and open ends INSIDE the rear frame rail. I guess this was to protect it from road mud, etc. Any fuel will simply dribble out the bottom of the frame rail
First, the fuel cap should be a "pressure / vaccum" cap which does NOT mean that it is operationally vented for the engine. This means that if the tank develops excessive internal positive or vacuum pressure, the cap will RELIEVE.
The operational vent is done by the evap emission system, part of which is in the tank (this changes over the years 70-later) and the 1/4" tube which comes to the engine bay. THAT tube is not only part of the evap control system, and originally ties in with the engine bay "carbon can" stuff, but ALSO IS THE operational vent, allowing the tank to properly vent during driving
If you don't need nor want the evap controls, that 1/4 line MUST be up high in the engine bay--to prevent siphoning, and must be left open. You can plumb it into the open air side of the PCV AKA the vent line to the filter bonnet.
If you don't want to do that, figure a safe way to install a fitting up high in the filler neck and convert the vent to a 69/ earlier vehicle. Those used a completely sealed cap
I WOULD NOT RUN a vented cap because of the danger of dribbling fuel over the side when full, etc.
Below is the 69/ earlier style vent. Simple. BE CAREFUL when choosing/ replacing a cap. The caps changed almost every year. There is a "famous" photo posted on here by Steve, OldManMopar, that shows several caps from 70--to the end. They are DIFFERENT
https://www.forabodiesonly.com/mopar/threads/fuel-tank-vent.505304/
The secret of the simple old style vent is that the bend goes up high against the top of the quarter panel, and "breaks" any siphon. It simply goes down alongside the filler tube and punches through the floor gasket, and open ends INSIDE the rear frame rail. I guess this was to protect it from road mud, etc. Any fuel will simply dribble out the bottom of the frame rail