Fuel line Mod Questions- Confused

[Mako21]

Hello all,

I’m still new to this and learning as I go. I believe with the 90+ degree days and heat index at 105 the last couple days in Miami and foreseeable future , I am certainly experiencing vapor lock conditions.

After searching these forums and YouTube, I’m still confused in terms of where to route the return line from the 3 way fuel filter back to the tank?

1. Drop the tank, drill new fitting at the top and plumb/ run the return in?

2. Drill the fuel filler neck and plumb there? Don’t like this idea, as it would cause me to run a fuel line inside the trunk.

3. Run a 3 way brass tee to the tank and plumb it to the existing rubber feed line? Confused here as it will not return fuel to the tank, rather reroute it under some pressure back forward to the mechanical pump.

And with all options, do you run a one way check valve on the line so the vapors don’t push back into the filter?

Thanks.

 

[67Dart273]

Let's start with "what do you have," AKA year make model. Frankly no matter what you have you have covered the two options. Tank or neck. Done safely either is OK. I did not drill my tank, but rather used a sharp awl and then a tapered punch, tapping to work it open. This leaves a lip that gives you reinforcement. I put my return up high, just to one side of the sender. If you are not happy with brazing on the tank, doing this on the neck might be an option. "What I did" was drain the tank, plump my CO2 tank off the MIG (I use CO2 straight, not a mix) and ran a BUNCH of CO2 through the tank with the filler cap off.

For "a safety check" (yeah, redneck) I then stuck a piece of tubing into the new tank hole, let it lay outside the body, and put the filler cap on. Took a propane torch and lit the outgass and it would light and go out, etc. After awhile, the outgas stopped trying to light. I let if flow about another 5 minutes, and then got under there, CO2 still going, and brazed (silver brazed) the new tube in place.

USE A BIG TUBE like 3/8 in case someday you want to go EFI. I used 1/4, which was fine for the return filter, but will need to upgrade it at some point for the EFI.

What helped me the most:

The return system (using a Wix return filter), a thick carb isolator, and some guys use wood, and I went to a rear mount electric pump.

What you are fighting is this alcoholized fuel boils easier than the old straight gas did

 

[Mako21]

Interesting ideas there…sorry I didn’t mention it’s a ‘76 Dart stock 225 slant six.

 

[Professor Fate]

A '76 should already have a 1/4" fitting at the front upper right corner of the tank that was originally used as a vapor return line from the charcoal cannister. Plumb your return line in there.

 

[Mako21]

Thanks for the tip. I was unaware of this vapor return line and will check for it. Upon looking at factory manual it looks like the line routes to the charcoal canister. Easy as unplugging and routing a new fuel line there.

Are you guys installing a one way check valve also along the return line?

 

[67Dart273]

A '76 should already have a 1/4" fitting at the front upper right corner of the tank that was originally used as a vapor return line from the charcoal cannister. Plumb your return line in there.

STop telliing people this WITHOUT explaining. YOU CAN NOT USE that line UNLESS you do something "else" about fuel vent. THAT 1/4" LINE IS THE FUEL TANK VENT!!!

If you want to use that existing 1/4" line you have a couple of choices

1...Look the 69/ earlier, simple, vent line into the filler neck. Modify the neck and create that style vent.

2...Use a vented cap (The stock cap IS NOT vented, it is, rather a pressure relief "pressure vacuum" cap, that relieves excess pressure, either positive pressure or vacuum pressure in the tank.) I do not care for that solution, as the filler necks are all rather special and it may be difficult to even GET a vented cap, plus, you run the risk of fuel spills out on the quarter panel.

 

[Professor Fate]

Thanks for the tip. I was unaware of this vapor return line and will check for it. Upon looking at factory manual it looks like the line routes to the charcoal canister. Easy as unplugging and routing a new fuel line there.

Are you guys installing a one way check valve also along the return line?

Cars with California Emission systems already used the 3 nipple filters- the FSM should show the routing and where they tapped into the line, as well as whether they used a check valve.

 

[Heywodja]

I have a friend who burned his garage down when he was drilling a fuel tank, lost his 70 cuda' too. He pulled and drained the tank and left it out for a week or so and thought it was empty.

Since it is a gravity feed system, why not just try leaving the cap off for a couple of test drives to see if this cures the issue.

Sometimes the rubber lines get soft and will collapse under a slight vacuum, which basically shuts the fuel off. Might try swapping them out with new, I had a Chevelle that was notorious for this, had to sit for like 30 minutes before it would start and run again.

 

[Professor Fate]

STop telliing people this WITHOUT explaining. YOU CAN NOT USE that line UNLESS you do something "else" about fuel vent. THAT 1/4" LINE IS THE FUEL TANK VENT!!!

If you want to use that existing 1/4" line you have a couple of choices

1...Look the 69/ earlier, simple, vent line into the filler neck. Modify the neck and create that style vent.

2...Use a vented cap (The stock cap IS NOT vented, it is, rather a pressure relief "pressure vacuum" cap, that relieves excess pressure, either positive pressure or vacuum pressure in the tank.) I do not care for that solution, as the filler necks are all rather special and it may be difficult to even GET a vented cap, plus, you run the risk of fuel spills out on the quarter panel.

Settle down, big guy.
The 3rd nipple on the (California only) fuel filter in question is not a liquid return, it is a "vapor separator" that (although not specifically shown in the FSM) gets plumbed into the vapor return line.

(sorry for the sideways pic, can't rotate it on my phone)
The fuel tank filler cap, however, is vented (all cars, Federal & California,'75-'76 at least) FROM THE FACTORY. It relieves pressure/vacuum variations not handled through the EEC (Evaporative Emission Control) system.

The overfill limiting valve acts as a check valve to prevent any backwash of fluid (either from tank or from vapor separator) from getting to the charcoal cannister.
Long story short- yes, he plumbs the third nipple to a tee in that line.