Vintage Mustang Forums banner
  • Hey everyone! Enter your ride HERE to be a part JUNE's Ride of the Month Challenge!
  • May's Ride of the Month contest ended with a tie! Go to this thread to vote on the winner! VOTE HERE
1 - 11 of 11 Posts

·
Registered
Joined
·
579 Posts
Discussion Starter · #1 ·
Hi guys,still trouble shooting my resto before she goes on the road! I was running the stang tonight in the shed and walked around the back to hear a hissing noise! upon investigation there was a hell of a vacuum in the tank at the cap! I replaced the old tank a while ago along with a new filler neck,hose and cap,should have i got a vented cap to stop the vacuum? are they even available? cant seem to find any in the catalogues TIA
 

·
(actually Slim Jr now)
Joined
·
24,597 Posts
Yes you need a vented cap unless your car is set up with the California type fuel vapor capture system!
 

·
Registered
Joined
·
1,292 Posts
All of the caps we sell now are vented. Some of the big block Shelby's came unvented but that was about it. They had to put caps on these that didn't vent because a back fire on some of the big blocks would ignite the gas fumes coming from around the cap and set the entire back of the car on fire. FORD was sceptical at first that this was happening, until it happened to them while filming a TV commercial! LOL!
Thanks, Doc
 

·
(actually Slim Jr now)
Joined
·
24,597 Posts
So how did they get around the vent problem?
 

·
Registered
Joined
·
12,304 Posts
I should hope you have vaccuum back there. Plug that and I bet your tank will crumple like tin foil (Well, exaggerated). Less fuel in the tank means something has to go in to take it's place.
 

·
Registered
Joined
·
579 Posts
Discussion Starter · #6 ·
bugger,I,ve already purchased a new cap some time ago and cannot return it! can i modify the one I have or should i bite the bullet and purchase a vented one ? TIA
 

·
Registered
Joined
·
579 Posts
Discussion Starter · #7 ·
well we've established that my cap is vented by sucking (till blue in the face)the centre section of the inside of the cap and air passes through freely!Is this a fair test? My tank collapses only on the top before I notice the vacuum and release the cap! any other thoughts on this? TIA
 

·
Registered
Joined
·
1,184 Posts
enlarge the vent hole with a 1/16 drill bit.

to answer Slim, they went to a closed vent system with a ventline to the carb/aircleaner.
 

·
Registered
Joined
·
2,340 Posts
JohnnyK,

Well, maybe not exagerated. Here's a couple of pictures of a collapsed tank from the concours board:
Collapsed Tank

The cap needs to be vented unless you have a '70 with California emissions, or a '71 on up with the vent to the carb. IIRC, the Shelby's that had the "afterburner" problem (resulting from the center mounted exhaust tips) also received a separate vent.

Carl
 

·
(actually Slim Jr now)
Joined
·
24,597 Posts
...vent line to carb...? Maybe you're referring to CA cars! I have a
'68 289 2v and a '70 351C 4v. They both have vented cap, open system.
 

·
Registered
Joined
·
579 Posts
Discussion Starter · #11 ·
didnt really want to drill out the hole much bigger , It's a 3/16 hole as it is ! I'm scared to go too large,my old cap has a hole the size of a pinhead and the car wasnt running when I purchased it so could not tell if there was a problem with it! the new cap is from Scott Drake,anyone care to look at the vent hole on there stang for comparison? TIA
 
1 - 11 of 11 Posts
Top