Slow fuel filler 308

Those 3 small tubes on the top of the RH fuel tank are upstream vents, but the final downstream vent that they connect to (that would release over-pressure from inside the tanks to the atmosphere) is in the charcoal canister. Are the three small lines on the top of the RH fuel tank still connected to the Liquid-Vapor Separator, and, if so, where does the single line on the top of the Liquid-Vapor Separator go? If you are going to be without charcoal canister (and have the Liquid-Vapor Separator present), extend the single line from the top of the Liquid-Vapor Separator to extend down below the bottom of the frame and leave it open to atmosphere. Otherwise, post a diagram of how your fuel system is plumbed now.

Is you present filler tube path more horizontal than the near-vertical stock filler tube path? (That won't help things.)

 

You mean that those 3 small tubes are just left open to the atmosphere? Would think that liquid fuel would just slosh out when driving with a full tank if they are open -- are you sure that they haven't been "blocked" somehow?

 

Can you post some images of the top of the gas tanks?

 

Seems to me your issue is most likely caused by the modified filler neck. If that unleaded flap valve wasn't there, the tanks would be very able to exhale out of the filler neck as the fuel is goin in. Adding back the connection between the vent crossover tube and the filler neck would certainly help, but only if the that connection point was above the unleaded flap. The two small vent lines are intended for evap recovery, and not to function as system breathers. They should not be open to atmosphere.

 

Can't agree that the three small vent lines on the top of the RH tank are not to function as system breathers, as on the sealed US system (when not refueling), air going thru those three small lines is the only way that outside air gets into or out of the tanks. Do strongly agree that the three nipples themselves should not just be left open to atmosphere. Would also agree that what was done at the filler neck is probably a big contributor to the OP's issue. I can't recall just how "sealed up" the metal plate in the US filler neck (that only allows unleaded fuel nozzles to be inserted) is, but I don't think it is a total seal (but still relies on the filler path being more vertical than horizontal, and not being some sort of long narrow tube -- the fuel nozzle basically just goes into the "open" top of the LH tank with the stock design) -- can a '78, or later, US version 308 Owner post a pic looking into the open filler neck?

 

If Steves information is not ringing an alarm bell it should. Your fuel system needs some plumbing attention beyond just being able to fill it. As it is now it is a first class fire hazard and needs an over all look at to correct filling and breathing to make it safe.

 

It appears the crossover vent tube for fluid displacement is still there, but this is a problem (red circle)
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Steve, for my 3.4L restomod, the charcoal canister and vapor recovery systems are gone. I was considering just capping the 3 vents on the passenger side tank and relying on the one available vent on the the driver side tank. Now I'm thinking running of 3 individual vent lines from the passenger side vents to the bottom of the sill, to prevent spillage if inverted yet intact. Will this increased vent capacity allow me to fill faster? bill

 

What year/model US version 308 do you have? You are confusing me a little because there is no open vent on any US 308 stock driver's side tank, but maybe the line going from the top of the LH tank to the fuel-vapor separator has been repurposed? Can't say that I'd be a visual fan of using three separate small lines (and would think that having some sort of manifold, or using the stock fuel-vapor separator, to join the three small lines to a single, larger line that is then extended down below the chassis would look cleaner), but, yes that probably would help if you are having trouble with the fuel fill rate. Certainly something you can try without much grief/effort to test.

 

Hi Steve. It's a 1978 GTS (Years ago I bought your OE 308 muffler, which eventually died and I replaced it with a used Larini on the new build). I repurposed one line on the LH fuel tank to serve as a vent. The 3 separate lines from top of RH tank originally routed to the vapor separator, don't look great when terminated at the sill, but are functional and likely hidden from view by wheel well liner. A 3 into 1 larger vent line, while possible, may be harder to route and then what to use for manifold? Bill

 

I think the flap is to keep someone from siphoning out gas.

Also, when I replaced the hoses on mine I found there were no ground wires on the tanks, or the crossover fluid and vent tubes.

 

My GTSi has some trouble with some pumps. Only if you fill at a very slow pace, it constantly clicks off. Very annoying. The evap system is totally stock, and every hose is correct and in great shape. The tank 3-way valve works great and satisfies all of the pressure specs. The rollover valve also works as intended. I checked flow into the charcoal canister, and it breathed smoothly when I tested it with compressed air. My GT4 fills with no issues. What else to check?

 

My 328 (totally stock) does the same with some pumps - if you pull the pump trigger all the way the pump will auto-shutoff rather quickly. On most pumps it doesn't react that way. Of course, some gas pumps/nozzles have a higher flow rate than others at 'full throttle' and since there is no standard (AKAIK) for fuel delivery/fuel acceptance, it makes sense that some high-flow pumps might be able to deliver more fuel than then a vent system on some vehicles can handle. I have found that when that happens, pulling the nozzle slightly back (up) from fully against the filler pipe restriction usually allows full flow.

 

Have you tried rotating the filling nozzle 180 deg from what would be the "normal" position (so the hose entering the back of the nozzle comes in from the top)? Definitely helped on both my ex-308 and ex-TR (but I'd never go "full blast" on the fill rate with so much paintwork at risk below the fill location).

 

Yup. It's a random but relatively common occurrence. I've tried inverting the pump handle 180 degrees (and 90, and 45). Sometimes it seems to help, sometimes not. The only thing that really seems to work with some consistency is to throttle the flow to down to approximately 30%, or what seems to be much less. The other thing is to find that special station where the pump nozzles just seem good.

The Ferrari filler arrangement seems so straightforward. ie, Very large straight-ish bore to the tank. Very well-vented (in both tanks). Reasonable pressure limit (~1/2psi) and good flow beyond that. It's probably soo simple, but I'm not seeing it.

What is the mechanism that makes the fuel filler nozzle shut off? Is it 'spits' of fuel that get recovered? When the fuel vapor contains more liquid, it senses fill and triggers? I just had another thought....... On the GTS/B, there is that very short metal filler with a very short rubber hose connecting to a large Ø tank nipple. What if the alignment of the nipple to the short hose joiner is connected such that it presents an edge where fuel comes in? In other words, it is not perfectly straight, so the fuel hits the edge and splashes back up on nozzle causing it to sense too much liquid fuel and triggers??? OR, that hose must be a tight 'clean' fit. The GT4 has that much longer smooth bore filler neck. What if the hose were replaced with another high-quality gasoline rated hose, but the Ø was slightly larger? My other vehicles do not have this problem, and all of them do not have that very short filler neck connection setup. Hmmmmmmm.
This might be way off base, but I am low on ideas.

 

Explained here:

https://auto.howstuffworks.com/fuel-efficiency/fuel-consumption/gas-pump-full-tank.htm#:~:text=When%20gasoline%20in%20the%20tank,and%20flips%20the%20nozzle%20off.



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Thank you for this.

So, this supports my theory that fuel that splashes back onto the nozzle tip where that 'sensor' hole would trigger it to shut off, and not some flow causing back pressure problem.

I know the hose from the factory is tight and is 'great fun' to install. The hose I used was a gasoline-rated American-made hose which was a relatively clean fit, but not tight. I think tightening down the clamps could deflect the inner hose wall away from the bead in the metal filler neck away from the surface presenting an edge to cause fuel to splash.

It's a theory that convinces me to find a better-fitting (tighter) rubber connector hose.