Technical Gas Smell - need advice

Hi all -

I've got a gas smell on my 31 Roadster that I'm trying to sort out (just purchased about 6 months ago). It's definitely coming from the tank area - I've replaced every inch of fuel line from the tank to the carb with SS 3/8" line and rubber to connect the sections. No leaks there - inspected while off and while the car is running. I primarily get the smell when the tank is freshly filled and until it's about half full.

The tank I have I suspect is "setup" incorrectly and it's only an 8 gal tank so I've been thinking about replacing it anyway, but before I spend $300 for fancy aluminum tank I feel somewhat obligated to make sure I've ID'd the tank as the problem.

So, the tank has a filler tube sticking at a slight angle from the upper top side of the tank - you cannot fill to the top of the tank so there's always about a 2" air gap even when full. Next to the filler is a smaller neck with a 1/4" hose that feeds to the fuel line/pump. The way it's connected now there is no vent setup and the cap I'm running is not a vented cap - I checked NAPA and they could not find a vented one my size.

if I feel around on the bottom of the tank - I can feel a plug down there. I'm wondering if that is supposed to be where I should have the fuel line connected and that little neck should be the vent. And I'm basically wondering if I had that connect like that if that would solve my gas smell.

The tank is raised a bit from the floor of the car and I can see what I would say is a wet spot, but it doesn't ever appear to be freshly wet and I can't seem to find how it would get wet anyway (nothing nearby on the tank that would lead me to believe there's a source).

Sorry for the long post and the vagueness. I guess I just need someone to tell me to shut up and put the CC down and be done with it. haha.

--Jon

 

probably a seal that leaks a little when full. Being an 8 gal tank just replace it with a decent size one.

 

It's a roadster, just drive faster

Does the car run ok? As gas gets used air needs to replace the volume of space the gas previously occupied So your tank must be pulling air/leaking fumes from somewhere. If your caps sealed and there's no vent this must be happening somewhere it 's not meant to, hence the fumes.

 

I agree with scott51, the cap can create mystery fumes either by leaking or pushing fumes elsewhere. I am sure you will find it. You may also want to check motorcycle gas caps for fit.

 

The bottom plug is to drain the tank,,you also need a vented cap or a vent.

Check the gasket around your sending unit,if there is no vents of any type there will be pressure in the tank when it expands..the fumes could be associated with that gasket. HRP

 

If all else fails...

 

Find someone with a smoke machine and test for leaks the same way we do on modern cars. Fuel is nothing to mess around with. I suggest testing it cold as that is the greatest possibility of finding the leak if it exists. Good luck

 

I agree with the concept that the tank is currently venting somewhere or the car would stall going down the road after the fuel pump created a vacuum in the tank by pulling fuel out. You have to have air going in from somewhere to replace the fuel. or it creates a vacuum.
Are you positive that the 1/4 inch line is the line to the fuel pump and not a vent line that has a hose running up into the body work somewhere? 1/4 inch is damned small for a fuel line unless you are running a small four banger.
In the last few years guys have pretty well gotten away from connecting a fuel line to what amounts to the drain fitting in the bottom of the tank. the reason is that if you get a leak in the system either at the fuel pump, line, hose of filter that is below the fuel level in the tank the gas will drain out of the tank.

 

Thanks all for the responses. It's possible that it's the gasket around the sending unit. I had considered that. There's no other connections other than what I mentioned so I probably need a vented cap to use this tank properly. I have not had issues with stalling - just drove 100 miles back and forth to Billetproof over the weekend and the car ran perfectly other than the gas smell. It's got a SBC 350 so it's sucking some fuel down.

Regarding the port next to the fill - it's 1/4" - am I sure it's supposed to be a vent or not? Nope the fuel pump is all 3/8" so I had to put a reducer in to make sure everything was tight there. The filler pipe was cut and there's about a 4" section of hose that connects to the cap housing- then the cap.

I could easily find a different filler neck and cap at the boneyard and get a vented unit. As I've replaced more and more fuel line and new cap, the smell has been worse - so it's venting someplace and I'm guessing if I find it at this point, I'll cause the stalling issue without the vented cap.

When I start to add up a boneyard trip, sending unit gasket and crossing fingers that solves it after that time, I think I'd rather invest the time/energy into a new tank. hmm.

Thanks all for the sanity check. Sounds like I'm on the right path.

 

Check it with a match...kind of like the leaky intake manifold test only in reverse.