Setting up a new fuel system from scratch - this look good?

[fiat142]

Hello everyone,

I'm in the middle of a mechanical freshening up of my 1975 spider. (Follow along over here: https://www.instagram.com/fiat142/)

So far the process has been a fun learning experience, however I've hit a snag in planning out the fuel system that I could use some advice on.

I'm looking to put a new 32/36 DFEV Carb on to give it a little more pep, and at the same time redoing the fuel system because it had some major rust and smell issues (new tank, new lines, everything from scratch).

However, I'm not entirely sure what the best setup should be. Has someone done this before to offer guidance?

It looks like the previous owner has removed every emissions regulation component on the car. It's pretty bare bones under the hood (which I like) - which makes it not match up perfectly with manuals and descriptions of other people's cars (which isn't great).

Old System

Below is a picture of the old system removed from the car as well as the existing 32 ADFA carb:





And here's a nice diagram to explain the current system. Yes, that's all the hoses that were hooked up - looks like they just blocked the vapor hose(s) that went into the charcoal canister?



Now, when comparing this to the various fuel diagrams from my shop manuals it looks like some obvious things were done: new(ish) electric fuel pump in the trunk, no more check valves, and no more vapor lines from the charcoal trap to the carb.



New System

Lastly, on new 32/36 DFEV Carb (https://autoricambi.us/products/carbure ... -3236-dfev) I'm noticing there's no return nubbin. I'd assume it's regulator is a bit more sophisticated and can just handle it..?




So based on the above my initial thoughts are:

- Delete the return line all together & close it off on the sender unit on the tank.
- Put a check valve back into the fuel line for funnies.
- Get a 2 port charcoal canister (like what's on a fuel injected later years)
- Plum the canister up into the air filter (with check valve) similar to the crank case vapor line.

I'm super visual so to complete the thought here's a diagram of the planned new system. Note the direction of the fuel flow/check valves throughout.




Questions:

- Does this look like a sound plan?
- Is there a way to simplify it even more? Like, what's with the 3 lines out of the tank?

I'm a novice so any feedback, comments, or ideas would be helpful!

[18Fiatsandcounting]

Sounds like a good project. Some thoughts (some of which you perhaps already know):

1) On the fuel tank, the larger (5/16") line from the sender unit is the fuel supply line. I'm pretty sure it goes to the upper (horizontal) brass inlet to the carb, but don't hold me to that. My guess is that the brass inlet diameter will match this fuel line overall, in other words, if one brass line into the carb is 5/16" and one is smaller, the larger one is your fuel inlet.

2) On the fuel tank sender unit, the smaller line is the fuel return line, and it's 1/4" diameter. Same story as above as to which brass inlet to the carb this gets connected to.

3) Still on the fuel tank, the 3 smaller lines off to the side are the "vapor accumulation vent pipes" (my words) that gather the fuel vapors at the top of the tank from 3 different locations. These vapors then go to the "liquid/vapor separator" (that soup can sized thing mounted in the rear fender well) which lets the vapors pass but drips the liquid fuel back down the 3 lines into the tank. The middle line of this separator goes to a "check valve" mounted right to the front of the fuel tank, and it's a plastic thing with 2 connections coming out of each side. Vapors go in, and the vapors are then drawn up the "vapor return line" to the front of the car and ultimately to the bottom connection of the charcoal canister. I think this check valve can also admit air into the tank under certain conditions to prevent vacuum from building up in the tank.

4) The larger (3/4" or so) inlet to the fuel tank near those 3 connections is a drain back from the fill tube. I think this goes back to the day before modern gas pump handles, when the fuel could be pumped in so fast that it would bubble up the filler tube and then onto the ground if you weren't careful. This 3/4" tube catches this fuel overflow and drains it back to the tank.

5) OK, on the charcoal canister, I believe the top nipple goes to a vacuum source like the intake manifold. I also recall that the middle connector was supposed to be a source of hot air from the engine so that this hot air would "loosen" the gasoline vapors on the charcoal and these would then be pumped by the vacuum into the intake manifold. Again, memory is sketchy but this is probably pretty close.

6) Personally, I would just keep the charcoal canister. The whole system probably adds 10 pounds or so, and there is no engine performance impact. However, it does keep gas vapors from building up in your trunk or garage or wherever. Assuming it's working of course.

7) Your proposed fuel line diagram would probably work, but the one thing to watch out for is that you don't build up a vacuum in the fuel tank. If you do, the fuel pump won't pump fuel to the carb and your engine will die. Vacuum could build up either because you're removing gas and not replacing that volume with air, or the tank was hot at one point but is now cool and thus under vacuum.

8 ) Oh, and you asked about a carb with no return line. Many of my carbs have been this way, and I think the float needle valve is strong enough to stop the flow of gas into the carb even with the fuel pump cranking away. However, I've also had mechanical fuel pumps, and so I don't actually know if the fuel return line is necessary for an electric fuel pump.

Hope this helps!
-Bryan

[wetminkey]

Current "ADHA to DFEV" thread in the Performance section may help with most of your carb plumbing questions,....
Todd.

[fiat142]

Thanks for the great rundown and pointing me in the direction of that thread.

[tonym]

I kept the return line by installing one of these just before the carb in the fuel inlet hose. And kept the canister connected but removed all of the other emissions things. Runs flawlessly.

https://autoricambi.us/products/fuel-fi ... eturn-line

[SteinOnkel]

I would second the above suggestion.

It doesn't have to be from AR, any parts store will sell the same filter for a "1978 Jeep Wagoneer". Has an internal pressure regulator and Webers love it.

[fiat142]

Oh, interesting idea. I like the idea of recirculating, regulating, and having it plumed already in case I switch carbs in the future (which, knowing me is not unlikely.)

Planning out the parts list in the next few days. I’ll document the process and post back here for the next person.

[wetminkey]

I used a WIX 33040 fuel filter which plumbs a little easier,...same result. My electric fuel pump takes care of the pressure regulation,...

[baltobernie]

Lots of good ideas here. With the new wiring and plumbing, you might consider an inertia switch inline with the fuel pump. Such a switch will cut power to the pump in case of a collision.
http://www.fiatspider.com/f15/viewtopic.php?f=6&t=35114