i know gas tanks are suppose to have some way of venting pressure and and letting air in so gas can get out but i am not sure were it is on my 81 and i think it might be my problem. about a week ago i was cleaning out my truk and my mom pointed out that my truk was leaking. apparently gas decided to make its way out of the return line that had been disconnected. i hook it back up thinking that i had fixed the problem but i think it made it worse. the next day i go out to start it and it would not even turn over. i just thought it was a bad connection at the battery until i went to switch carburetors and and fuel just kept pumping out of the fuel lines. anyway i go and open the gas cap and all i hear is the sound of air rushing into the gas tank for a couple of seconds and gas stops pouring out the fuel line. because gas just kept pumping into the engine i was forced to remove all the spark plugs and turn the engine over till all the gas was out of the cylinders and then do an oil change. 11 liters of very gassy oil came out of the engine. obviously i want to fix the problem so that i don't want to have to waste another $30 on gas oil and a filter.

 

The tank should be vented through a line that goes up to the charcoal canister. I think what you heard was the air venting out of the tank.

 

the truck has no charcoal canister. i left the gas cap on for most of the day today and when i took it off i could smell the air rush out but it was just a very short burst of air unlike the other day where air was coming for at least 3 seconds.

 

Charcoal/vapor canisters started in 79 but that was only Canada and California models. I am not positive when they started to be universally used. I guess it was after 81. Pre-canister a vented fuel tank cap was used but I am not sure when they stopped using them. Is your cap of the vented type because they can go bad and cause what you experienced?

 

the truck might have had a charcoal canister at one point but the truk it is not stock. according to the vin it should have a slant 6 in it. i am guessing that the person who installed the v8 removed all the emissions stuff that it would have came from the factory with. i'm not sure if my gas cap is the vented type but i thought that is how all gas caps work. from what i can see there is 3 lines coming out of the sending unit and it looks like one of the previous owner might have done some of there own repairs.

 

No modern caps are vented by emissions laws. That is why the vapor canisters were brought in. You are going to have to trace the fuel lines to find out where and how he vented the tank.

 

this sucks. i have a feeling that the vent line might be blocked. i see 3 lines leaving the tank and i see 3 lines under the hood but only one is hood up right now.

 

i think i might have fixed the problem yesterday when i was replacing my muffler. i noticed a small rubber line leaving the top of the gas tank that had a screw in it.