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2 way vented cap

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Old 08-11-2018, 04:13 PM
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Mitty
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Default 2 way vented cap

Hi, I apologise if this has been asked before, but is the 63-67 vented fuel cap a 2 way type? Ie, vents pressure and vacuum. I want a 2 way for my 74 as I have no charcoal canister so need to regulate the tank pressure correctly

cheers, tim.
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Old 08-11-2018, 06:40 PM
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The 63-69 cap is a vented cap so you'll be fine with this.
https://willcoxcorvette.com/corvette...p-vented-63-69
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Old 08-11-2018, 06:45 PM
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Originally Posted by Willcox Corvette View Post
The 63-69 cap is a vented cap so you'll be fine with this.
https://willcoxcorvette.com/corvette...p-vented-63-69
thanks, so will that allow air in as well as out?
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Old 08-12-2018, 01:03 AM
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Originally Posted by Mitty View Post
Hi, I apologise if this has been asked before, but is the 63-67 vented fuel cap a 2 way type? Ie, vents pressure and vacuum. I want a 2 way for my 74 as I have no charcoal canister so need to regulate the tank pressure correctly

cheers, tim.
I believe those vented caps only allowed air into the tank to prevent vacuum. On my 74, my charcoal canister is long gone. I use a vented cap to handle vacuum and a "remote mount rollover vent valve" to handle over pressures. Some people have been known to just drill a small hole in their tank but gas will invariably slosh out.
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Old 08-12-2018, 04:56 AM
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My '72 set in the garage, next to the kitchen, wife has a sensitive sniffer for gasoline, ME not so much.....oh well, vette had an issue with tank, and the way to fix the problems is simple, really....number one is that I have a DPFI setup on my SBC..... so the fuel pump is in rear UNDER the tank, tied to frame rail, pushing fuel forward to rails, regulator goes back to tank up top on pass/RT side....just like it did with a carb decades ago....

BUT on top left/driver side is a black plastic float/check valve, takes the tank fitting and if fuel is present the float blocks the vent closed, that line goes forward to the charcoal canister , the canister has a manifold vacuum valve on it, pulling the discharge/vapor line from the canister open when engine is running, and that vent line goes to the PORTED vacuum opening on the throttle body....essentially same as with a carb, call it feeding into the inside of the air cleaner if you want, it's above the throttle blades.....

on my car I discovered a failure on the canister control valve, it was stuck OPEN for some odd reason....fine by me, I ran the rest of the lines per stock/usual and then got a two way vented cap on the tank.....

what WAS happening is the stupid stock cap was a closed type, here in FLORIDA the summer heat would combine with the heat of the returning fuel and cause a positive pressure in the tank, I could hear the air/fumes escaping when I went to fill the tank.....the sealing was not purrfect to the fumes would get into the garage air....

BUT with the float valve being not flooded/open, the fumes/pressures were sucked into the engine with the mild/ported vacuum, and PROBLEM SOLVED.....and so, logic tells ME, that running that line that went to the cannister, it can be run straight to the ported vacuum fitting and all should be fine....BUT that ASSumes the liquid check valve on the tank is operating correctly.....

Last edited by mrvette; 08-12-2018 at 04:58 AM.
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Old 08-12-2018, 05:18 AM
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Thanks for the info guys.
The reason I’m asking is that valve on the drivers side of the fuel tank, that feeds the canister is leaking onto the muffler, and I wondered if it’s due to there being a pressure build up in the tank, as I have no canister and the line to it is blanked off. I’m going to have a look, remove the valve and blank the pipe on the tank, but need a 2 way fuel cap. I’ve found one that states it’s 2 way on rock auto, so will go for that I think.
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Old 08-12-2018, 05:39 AM
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Originally Posted by Mitty View Post
Thanks for the info guys.
The reason Iím asking is that valve on the drivers side of the fuel tank, that feeds the canister is leaking onto the muffler, and I wondered if itís due to there being a pressure build up in the tank, as I have no canister and the line to it is blanked off. Iím going to have a look, remove the valve and blank the pipe on the tank, but need a 2 way fuel cap. Iíve found one that states itís 2 way on rock auto, so will go for that I think.
Fix the float valve, and do the way I said above, or you will have gas fumes in the garage.....
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Old 08-12-2018, 06:04 AM
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Originally Posted by mrvette View Post
Fix the float valve, and do the way I said above, or you will have gas fumes in the garage.....
Iíll give it a try, Iíll see what condition the valve and pipe is in.
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Old 08-12-2018, 10:04 AM
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I have a 74 also and had a problem with the canister couple years ago. I simply drilled a 3/32 inch hole in the gas cap and I have had no problems since. My car is kept in my garage adjoining our kitchen and have not had a hint of the smell of gas in the last 2 years.

Last edited by red topless gator; 08-12-2018 at 10:55 AM. Reason: size
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Old 08-12-2018, 08:00 PM
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Originally Posted by Mitty View Post


thanks, so will that allow air in as well as out?
Nope.. just in.. it won't allow the tank to vacuum lock. Honestly you don't need anything else if you use the vented cap. However the ideas above seem creative to me and the only issue I see with drilling a hole in the old cap would be that fumes could get out... On such a tiny hole, I'm not sure that it would matter..

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Old Yesterday, 01:40 PM
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I've owned drag boats, ski boats, motorcycles and several cars with vented caps.
Never had any issues with gas fumes in my garages until I bought my 73 Corvette.
Chased the fuel fumes for weeks before I found it was the valve on the tank that vents to the canister in the engine compartment.
I replaced the valve and no more fumes.
As part of my frame off resto/mod I'm eliminating the canister fuel vent and return lines.
I've purchased one of the vented fuel caps showed by Wilcox that will eliminate the canister, lines and fuel smells in my garage.
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Old Yesterday, 02:49 PM
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Hi, I found one of the pipes on the valve on the drivers side of the tank was sheared off. So I’ve blocked it, and see if that fixes the issue, plus the new 2 way cap.
Willcox, out of interest, when I tried to order the cap from you, postage came up at $55 to the U.K. plus I’ll need to pay import fees, which makes a $25 cap $96. Whys postage so high?
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Old Yesterday, 06:03 PM
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Napa Auto also carries the caps.
Google Stant gas caps for a 68 to 69 corvette.
Their website has a cross reference part numbers page and you may be able to find someone who sells the caps or can get one in the UK without paying the overseas shipping.
I believe Stant manufactured the OEM gas caps for Chevrolet back in the day.
Good Luck.
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Old Yesterday, 06:46 PM
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Hi, yes the cap from rock auto is stant. Theyíre shipping costs are excellent to the uk. I donít know why thereíre so much cheaper than all the big corvette parts guys in the USA. Example, ecklers wanted $738 shipping for a rear trailing arm assembly, on top of the cost of the arm! We have to pay 20% vat on goods and shipping fees.
Sucks buying corvette parts here.
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Old Today, 01:55 AM
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Glad you found a cap.
Sorry things cost so much to be shipped over there.
I recently sold a sbf 408 cu in and a Tremek TKO -600 to a guy that loaded them into a shipping container with a bunch of motors and other Ford goodies
He and his partner were in the business of purchasing and shipping performance equipment from the States to Europe.
He said they were making a fortune and they had problems filling the orders as fast as they came in.
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