Nicky B

I bought myself a very nice 1971 350 automatic at the weekend, I have only driven it 5 times and it has a strange fuel leak problem.

There is no problem when the engine is running but twice after I have parked her up fuel (I guess about 1/2 a pint) drips out onto the floor and then stops, the first time it did it overnight in my garage so I couldn't see where it came from but the second time I had just got out of the car and I saw the petrol dripping out (quite quickly). I don't know where it originates from but it ends up coming out of a chasis crossmember just behind the front wheel on the drivers side, which is strange as the pump and fuel line from the tank run along the passenger side as far as I know. The car is standard apart from an Edelbrock carb & intake manifold and the filler cap is a sealed, non vented type.

Any ideas gentlemen please?

Nick.

HeadsU.P.

Vapor Canister perhaps. Look inside the cove on drivers side. Not sure if the 71s had them. From that, is a return line to tank leaking maybe?

red topless gator

I had the same problem with my 74, coming from canister. Vented the gas cap and no more problems.

Nicky B

Thanks for that idea, I'll vent the cap first and see what happens, if that sorts it I'll be very happy, talk about a cheap fix!

Nick

Peterbuilt

https://willcoxcorvette.com/corvette...or-valve-70-74

The fuel separator is on the top left side of the tank.
It allows vapor to pass to the charcoal canister but no liquid fuel.

Also don't fill the tank to the very top.

Nicky B

Thanks for the tip about brimming the tank, that's exactly what I did as soon as I got the car on Saturday!

resdoggie

Suggest you park it outdoors until you get it fixed.

BKbroiler

This is a very good suggestion.

GTR1999

Most likely that is what it is, the check isn't working, you fill it up it creeps down, you top it off and so on. Happened to me last year with my 72. I haven't had the time to replace it, so I fill it until it reaches the base of the neck and stop. When it's correctly working you can fill and it won't drain down right away. I figure I'll do it when I replace the exhaust I don't like all that much. Fill it when you go out for a drive and you'll be ok.

Nicky B

Thanks for all the advice guys, I have to say I'm well impressed to get so many replies so quickly, if I put the same post on the U.K. club forum I'd be lucky to get one reply in a week!
Probably because there are so few of these beautiful cars over here!

Nick

Alan 71

Hi Nicky,
Welcome!
AND a 71 in the U.K.!! NICE!!!
Perhaps you might want to remove the left side egg crate grill.
This will give you a good look at the canister.
I'll post a picture of the vapor separator on the tank too.
Regards,
Alan

The vapor canister.
Are the 2 rubber lines properly run from the canister cap and top to the carburetor?




The separator at the tank.
You can also see the vapor line running forward to the canister.

Nicky B

[QUOTE=Alan 71;1595872420]Hi Nicky,
Welcome!
AND a 71 in the U.K.!! NICE!!!
Perhaps you might want to remove the left side egg crate grill.
This will give you a good look at the canister.
I'll post a picture of the vapor separator on the tank too.
Regards,
Alan

The vapor canister.
Are the 2 rubber lines properly run from the canister cap and top to the carburetor?

The separator at the tank.
You can also see the vapor line running forward to the canister?

• Thanks very much for the info Alan, I'll check it out at the weekend and let you know how I get on.

DUB

I will 'say' this.

IF you get your problem solved by either a correct fuel cap (vented) that is not holding pressure in the tank. And your fuel leaks stop. I would disconnect the rubber hose that goes to the charcoal canister...and ALSO remove the fuel hose where the vapor line goes to your fuel tank area and blow air through it CAREFULLY and use COMMON SENSE due to you are messing around with fuel.

Reason being....due to this line should NOT have raw fuel in it...and seeing how it now does.....and you do not get the fuel out...the fuel that remains in the line will turn to varnish in time..and thus...effect the flow of this line. AND...if it happens again...and then THAT fuel turns to varnish...you can plug up the line....and then what happens is that moisture stays or gets in that line..and when it freezes....the line splits....and then when it thaws...you now have a raw fuel smell in your garage.

I have replaced many vapor return lines that they are not fun to do..and just trying to save anyone who reads this from that FUN.

DUB

7T1vette

The correct fuel cap for a '71 is a non-vented cap. The '71 has a vapor canister on it and that canister is the vent for the fuel tank. If you put a vented cap on it, you will negate any benefit of the canister at collecting fuel fumes.

But, you do have a problem and you need to identify the cause and resolve it. If putting the vented cap on temporarily will prevent raw fuel spillage in the engine compartment, so be it. But try to find the actual CAUSE of the leak, rather than just masking the problem.

theandies

I agree. 1971 Corvette fuel system was a closed system. If you have to put a vented cap on it then something is wrong.

DUB is correct, use major caution when messing with the fuel system Especially fuel vapors. Liquid fuel doesn't burn as easily as fuel vapors. If you do plan on keeping it in the garage and get fuel vapor smell I hope your hot water heater is not LP gas and if it is and it's in the garage I hope it's at least 2 feet above the garage floor and in its own storage closet. Gas vapor is heavier than air but can accumulate.

The fuel vapor separator also has a check valve in it I believe so if fuel happens to get into the separator it won't go into the vapor return line up the the charcoal canister. You can see that the outlet of the fuel vapor separator on the tank is higher than the top of the tank. This alone should prevent raw fuel from getting into vapor return line. I never fully fill my tank up. I leave about a 1/4 to 1/2 inch lower than the top of the tank.

When the fuel vapor system or EEC (evaporative emission control) is working correctly you will get next to no fuel smell in the garage.

DUB

Hopefully it is know by all of those concerned that a 'vented' cap...DOES NOT vent fumes out through cap.

A vented cap allows air to be pulled in though the cap....into the fuel tank. And the air being pulled into the fuel tank is done with the emissions EVAP system

DUB

7T1vette

Yes, we know that DUB. But a "closed system" is a "closed system" -- until it's not. Perhaps the system would work OK with a vented cap. But then, why would GM specify a non-vented cap, if it wasn't needed?

The only things a vented cap might prevent are a collapsing fuel tank or a prevention of fuel flow from the tank because of internal negative pressure.

Nicky B

Thanks for all the advice about my petrol dripping issue, it turns out that the fuel vapour separator valve is knackered and it's only an issue if i fill the tank right to the top. I've order a new valve and will simply only fill the tank 3/4 full until I get round to fitting it.

Once again thanks for all your advice.

Nick

Alan 71

Hi Nick,
Glad to hear you were able to trace the fuel leak!
Hope you don't have to much reaching the separator to change it!
Regards,
Alan

Nicky B

Indeed Alan, I see from the forum that some people have managed it without dropping the fuel tank so fingers crossed! Nick