Hadez

All the suppliers offer both vented & non-vented gas caps? I even see NOS GM non-vented lids on eBay. Why is there a difference and which one am I suppose to have for a relatively stock 69 L46 & Qjet setup?

murraybs

Vented caps are used mostly for emissions control. You could use either one, but for the sake of keeping fuel pressure more consistent, I'd go with the vented cap.

Hadez

thanks...

LB66383

Vented caps were pre-emissions. When vapor canisters were added to cars, non-vented caps came into use. You shouldn't mix them -- vented for non-vented, and vice versa.

dennis

Your 69 L-46 absolutely uses a vented cap.

Its not ENTIRELY true that vented caps were pre emissions, and sealed caps came with the advent of emission/ vapor canisters.

That weird bird of 1970, (at least the L-46 with a 207 carb), uses a sealed cap- no canister. Topic of much confusion and frustration

68/70Vette

My 1970 BB has a non-vented cap and an an emission canister.

About the vented/non-vented cap situation. All of the fuel tanks are vented. The 1968 and 1968 vented the tank via the cap; the cap has built in air passages to vent the cap. In 1970 (at least for my car), the tank is vented via the emission canister located in front of the passengers firewall.

Barry's70LT1

I also have a sealed cap and No canister.

dennis

The L-46 in 70 only uses a canister for the calif model.(ECS system)I believe the BB is that way as well.

BTW vents from a valve on top of the fuel tank

70BBvert

I think that was a Calif emissions requirement. My 70 BB was sold originally in South Carolina, non-vented cap & no charcoal canister.

Jim

Rudy's Stingray

Greetings!

My wife has been complaining about the fumes in the garage after a drive in the ole' girl (My car, not my wife).

It's a 1970 L46 with the vented cap and no canister.

So then, what exactly would happen if I opted for the non-vented cap?
I must say it does put out some strong fumes of fuel. I can't imagine thats a good thing.

Thanks.

Rudy

gbvette62

If your tank is not vented, then you must run a vented gas cap.

The effect of using a non-vented cap, is similar to what happens when you try to pour liquid from any canister, that doesn't have some form of vent. Non vented tanks using non vented caps, have actually been known to collapse.

If your getting serious levels of fumes, I'd think your problem is more than a vented cap.

You may have fuel leaking from the cap. I would try a new vented cap, or at least a new gasket, in your old one. Check the filler neck gasket and the sending unit too, as the o-ring on it could be leaking. I'd check the tank and fuel lines too. You may have a leak, that's enough that you smell fuel, but not enough to cause a puddle on your garage floor. Check the fuel pump and around the carb, to see if there is any sign of leaking around one of them.

texas jim

This is the correct answer. You ned some type of vent. W/ the canister, your venting goes into that canister from the tank. I have in the past used the 1/4" vent line as a return line, installing a "T" just before the carb, on the fuel inlet line to keep the fuel from getting hot. Then I would use a vented cap, swapping the non-vented f/ the vented. Proper venting is important. If you have a non-vented cap and no canister, then you have a vent from the tank stubbed off in the rear. The fuel vapor smell could be afew things. How about your carb, float level high/ fuel bowl venting, is the carb acting up at all?

...Roger...

Most books say all 70s use the sealed or non-vented cap,I believe they are wrong.
I agree with most in that if it doesn't have a canister it should have a Vented cap.(there is a built in vent in the tank but I think that is a catastrophe vent not intended to be the regular vent)

I agree with gbvette you most likely have a leak that doesn't show up on the floor,the most common I've seen is the fuel line or return just below and behind the passenger seat where the line takes 2 90 degree bends and the line lays in the frame gusset and rusts or rusts in the retainers just forward of the gusset. Put your hand under there and feel to see if its damp after parking the car for a few min.

69ttop

My vett is a 1969 L46 350 350 with a rochester carb. The car is totally stock and my orignal tank cap is VENTED. As for the gas smell in the garage, if its not from thr engine compartment a common cause is a dryed out cork fuel tank fill neck gasket. I had the same smell until I restored the car and found that gas sloshes in the tank when you drive the car and leaks out between the tank and the fill neck and coats the top of the tank. The gasket is cheap and easy to replace. If it is not the cause I would replace the 40 year old cork gasket anyway.

jetjockey

If you will replace the rubber cup and drain line around the filler neck, gas won't "coat the top of the tank".

...Roger...

The cork neck gasket is below the rubber cup.

Barry's70LT1

This is not really correct. I "do not" have a canister and "do" have a sealed cap. I'm the original owner and it's the original cap/tank.
Just trying to keep the facts straight. Thanks

gbvette62

LT-1 was different than the other engines. It used it's own unique tank, and did not use a fuel return line, like the Q-Jet engines did.

...Roger...

So do you guys think the vent in this picture is what is venting Barry's70LT1's tank ?

Mike Ward

This is true but the return line has no bearing on tank ventilation. I'm curious to know how cars with no vapour canister but with a sealed cap allowed air into the tank.