Fuel tank area gas vapor smell

[DTZ]

Hi Guys,

I have the original, all rubber type tube that goes to the fuel neck, in good shape. I changed the small vapor lines to the canister lines and tightened up all the clamps.No smell at the gas cap. sniffing around it, seems to be the fuel neck side

I still smells like gas in trunk and cabin. Any ideas how to find the source of the  leak?

[datzenmike]

Assume this is for A 510?? You should say this and the year. There are some differences between years. Someone may have had this exact same problem.

 

Hows the vapor line to the flow guide in the engine bay?

[Ranman72]

I have a 68 510 with the all rubber filler hose if my memory serves me correct mine looked to be ok but it was leaking fumes 

i replaced the filler and the vent hose there is no expansion tank in the 68 it just loops back to the tank 

 

it also could be the fuel line at the bottom of the tank or the factory cap on the return line as the 68 also didn't have a return line 

assuming you have a 68 or 69 510 

either way check all fuel hoses / clamps if in question replace 

sometimes vapors can leak even if you see no fuel leak 

[DTZ]

Okay, mine is a1970. I will check the bottom and other spots.

Thanks..

[DTZ]

Yes, 1970 510. What is a flow guide? I do know the return line to the tank is good.

[datzenmike]

The flow guide valve directs vapors from the gas tank vent pipe into the engine crankcase to be stored when the engine is off. When the engine is running the PCV valve draws these fumes into the intake to be burned. As the tank empties the flow guide valve allows filtered air from the air filter back into the tank. To work properly you need a non vented gas cap. The flow guide valve is bolted to the left (driver's) side strut tower near the steering box.

[DTZ]

Yes, I have the non- vented cap. The flowguide is connected per the diagram...

[datzenmike]

The flow guide valve is a very rudimentary emissions device that is ignored because no one knows what/how it works. Engine will run with or without it but may emit fumes.

 

On later models it was replaced by the charcoal canister, a much better idea. 

[DTZ]

The fumes are  in the trunk.

[datzenmike]

You have the little tank above the gas tank? Must be a hose or hose clamp. I think the outlet and return are in behind and you have to pull the tank out to get at them. You might be able to remove the rear seat back to get a look.

[DTZ]

yes, I have the small tank up where the trunk lid  hinges are, those are easy . as for the fuel tank, I will have to pull the seat to take a look, I didn't think to look there.

Thankyou!

[john510]

6 hours ago, DTZ said:

yes, I have the small tank up where the trunk lid  hinges are, those are easy . as for the fuel tank, I will have to pull the seat to take a look, I didn't think to look there.

Thankyou!

I had the same problem at one time.Replace every hose you can and make sure clamps are tight.Mine looked to be in good shape but smelled.I never found the culprit.Nothing was obvious so i just replaced everything and the problem was solved.

[DTZ]

Yeah, that's probably what I will have to do..

[Wiz]

Hi All,

 

I have a similar problem I have an original 1968 Fuel tank - the engine will be an L18 with a 32/36 Weber.

 

My set-up has zero emission control. Do i just ignore it and put it back together as it was installed.

 

The original set-up had an 8mm line capped off near the fuel filter and a 6mm line that ran from the tank to the fuel filter.

 

The emission control is a small pvc tube that just runs above the tank but is connected to nothing..

 

[datzenmike]

The line from the tank to the fuel filter is the supply line.

 

The line that was capped and near the filter was likely the fuel return line. It may or may not have been used in your 510. In operation fuel is pumped to the carburetor and past it and back to the tank. In the return line near or on the carburetor is a restriction so that the gas builds pressure against it or the gas would simply take the easy path back to the tank. The intent is to slowly circulate cooler fuel past the carburetor and return it to the tank. This makes hot weather re starting much easier by eliminating vapor lock where fuel boils in the lines or in the carburetor. It also constantly, though slowly, filters the fuel tank contents over and over. It's common for return lines to be larger diameter than the supply line.

 

Does the cap on the end look like something from the factory? or is it likely from a previous owner?? Possibly the carburetor was changed and the return line made unusable?

 

*Do you have dual points? You may not but if you do, the throttle linkage would have a switch assembly on it to turn them on and off under certain conditions. This introduces a retarded ignition to reduce emissions in certain gears and throttle positions.

 

*In N America the 510 had a sealed fuel cap and the tank had a vent line from the tank to the left side strut tower and connected to a flow guide valve. The purpose was to collect any fuel fumes that evaporated from the tank and store then inside the crank case till the engine was started then the PCV valve would draw them out into the intake and burn them. f this line is disconnected the fumes are free to escape most especially at the engine end.

 

The PCV valve is an emissions device but it's real value is it keeps the inside of the engine cleaner and extends the oil changes by removing acidic water and fuel vapors and combustion blow by that would dilute the oil. 

 

*These may be a N American feature only.

 

 

 

 

[Wiz]

Thanks for replying Datzenmike 

 

It looks factory to me - See photos below 

Also, inside the fuel tank it looks like the 8mm line is sealed. 

 

I have looked everywhere I don't think I have a flow guide valve. Just off the photos in the forum I have never seen anything like it on my car.

 

I have taken heaps of photos of my current set-up. Maybe there is something I'm missing.

 

What do you think the best options are?

 

On a side note: The fuel tank was very clean internally, but I decided it to give it a rinse (not sure why). The next day there was like a rust/bacteria infection on the baffles.

 

I've washed the tank with Evaporust, and then coated it with fuel. The rust has stopped but it pretty much won't come off now. It looks more like a stain then rust. First of many lessons learned...

 

Photos below:

 

 

 

 

Old tank with Clear tubing breather?

 

Filler hose - The bottom part ripped off during removal

I am going to extend the middle section with a piece of 57mm Aluminium pipe.

 

Capped return line 

 

Evaporation hose??

 

Current view.

 

Rusty baffle - After one day 

[Wiz]

[datzenmike]

 

Definitely NOT factory. Even the hose clamp is not.

 

 

Flow guide valve is just under the air filter snorkel on the left strut tower. Your tower has the dimples but doesn't look like they were drilled out. 

 

 

 

Not sure what carburetor is going on here but as you can see it's very limited by having to flow through basically the tiny 30/34mm stock carburetor holes. Sort of like a NASCAR restricter plate

 

[Ranman72]

if the tank was rinsed with water the stains/rust is no surprise a solvent or gasoline would have been a better choice if water was used 

also the capped return line has the wrong clamp to have been factory and the hose is not factory either 

the factory caps were rubber like a thimble with a wire hose clamp 

 

Edited November 11, 2022 by Ranman72

[VintageFerrari127]

You may consider looking into an aftermarket charcoal canister such as the following: https://www.classicperformancerestoration.com/product-page/charcoal-vapor-trapper

 

I've experienced a similar issue on several customer vehicles, and I typically use a charcoal vapor canister to solve the issue.

[datzenmike]

The older Datsuns has a flow guide valve that, when working, directed and stored gas tank fumes in the engine crankcase. It works just fine though they were later replaced with a much better charcoal canister.

[Wiz]

Thanks for the replies.

 

So what is the best option, should I try and find a flow guide valve and install it.

 

I have installed the tank, based off the diagram it shows the breather going into the filler neck and the other end discharging to the underside of the vehicle (no canister just where the fuel lines go.

 

The return line cap is not original, but the funny thing is the outlet inside the fuel tank is sealed shut. Has anyone ever heard of this?

 

Below are some photos of the fuel tank install. The neck rubber was damaged for the last 30mm, so I created an extension with aluminum.

 

I got most of the rust out and put some fuel in the tank. So hopefully that should be the end of that problem.

 

 

 

[Wiz]

On 11/10/2022 at 1:16 AM, datzenmike said:

 

Definitely NOT factory. Even the hose clamp is not.

 

 

Flow guide valve is just under the air filter snorkel on the left strut tower. Your tower has the dimples but doesn't look like they were drilled out. 

 

 

 

Not sure what carburetor is going on here but as you can see it's very limited by having to flow through basically the tiny 30/34mm stock carburetor holes. Sort of like a NASCAR restricter plate

 

This was on the original intake manifold.

 

I am using 32/36 Weber Downdraft with this adapter plate that comes with the kit

[datzenmike]

Will the 2bbl Weber adapter not fit directly onto the manifold without that 4bbl one??

[Wiz]

Yep it will

I just put it on top for the photo.