Fuel tank pressure

Screwz

Not-quite-so-new-guy
May 10, 2021
23
13
Arkansas
I just bought an 87 Caballero and on my way home with it I stopped and put gas in it and noticed pressure in the gas tank. the place I bought the car from had just replaced the carburetor that was on the car because it was dumping fuel into the engine.I replaced the gas cap with a new vented cap . I’m hoping it was just that simple. I was wondering if this car/truck could have came with a non vented cap because it was fuel injected .
 

pontiac guy

G-Body Guru
Oct 28, 2016
548
93
Royse City, TX
I just bought an 87 Caballero and on my way home with it I stopped and put gas in it and noticed pressure in the gas tank. the place I bought the car from had just replaced the carburetor that was on the car because it was dumping fuel into the engine.I replaced the gas cap with a new vented cap . I’m hoping it was just that simple. I was wondering if this car/truck could have came with a non vented cap because it was fuel injected .
All cars came with non vented caps beginning in the 70s. The tank vent should go to the charcoal canister. The fuel bowl will also vent to the charcoal canister. The charcoal canister will purge back into the motor and is vacuum controlled. Are you sure you had pressure in the tank, not vacuum? If the vent system is capped off you will slowly create a vacuum in the tank by drawing the fuel out.
 
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Screwz

Not-quite-so-new-guy
Thread starter
May 10, 2021
23
13
Arkansas
All cars came with non vented caps beginning in the 70s. The tank vent should go to the charcoal canister. The fuel bowl will also vent to the charcoal canister. The charcoal canister will purge back into the motor and is vacuum controlled. Are you sure you had pressure in the tank, not vacuum? If the vent system is capped off you will slowly create a vacuum in the tank by drawing the fuel out.
Thank you for the information. I’m not sure if it was vacuum or pressure. Because it’s setting in my shop with a slow gas leak I haven’t started it. Honestly I haven’t had time to even look at it but I did check the charcoal canister and it’s not hooked up to the carb.I did check the tank again today and there was still a small amount of pressure or vacuum.
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I‘ll have to do some research and see if I can get this system work correctly with my set up. I don’t have a factory carburetor.
 

Screwz

Not-quite-so-new-guy
Thread starter
May 10, 2021
23
13
Arkansas
The charcoal canister isn’t connected at all. I found my leak it was the line from the tank to the charcoal canister.I made a temporary fix. I need to get a fuel pressure gauge and see what’s going on. I’m still getting pressure in the tank. Maybe the fuel is bleeding pressure back into the tank.
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Ribbedroof

"That wagon guy"
Supporting Member
Jan 4, 2009
4,149
113
Wellston, OK
If that's the vent line from the tank that's cut off/crimped, you're slowly drawing a vacuum on the tank when engine is running.

No reason not to connect the carb bowl vent to the canister. Leaving it vented to the atmosphere will result in fuel fumes accumulating in the garage if it's parked inside. Possible fire hazard if gas-fired water heater is in the garage like they used to do.

I'd also look into replacing that LOOOONG rubber fuel hose, either with braided stainless hose, or a hardline with small rubber hose to connect to carb and feed line.
 
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Screwz

Not-quite-so-new-guy
Thread starter
May 10, 2021
23
13
Arkansas
I'd also look into replacing that LOOOONG rubber fuel hose, either with braided stainless hose, or a hardline with small rubber hose to connect to carb and feed line.
Like I said I just bought it and there’s a lot of stuff to fix .I want to make a hard line with a regulator and a pressure gauge.I’m also trying to figure out what to do with the gas tank vent /charcoal canister.
 
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