Is gas tank cap vented?, tank cap |
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Is gas tank cap vented?, tank cap |
tomrev |
Jan 9 2016, 02:35 PM
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#1
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Member Group: Members Posts: 231 Joined: 25-February 14 From: N. Mich. Member No.: 17,037 Region Association: None |
As I am finishing up new fuel lines, with clean, empty tank, it seems like the tank holds a slight pressure, when blowing thru the return line. I'll be using the bosch 044 fuel pump, which moves a lot of fuel, and want to make sure there is no pressure fighting the flow back to the tank. Does the stock '75 cap have any self venting property's, or does all the tank venting go thru the TINY vent port, that heads to the charcoal canister? If so, have any of you added a bigger vent, as a fuel cell would use? Thanks, Tom
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damesandhotrods |
Jan 11 2016, 06:05 PM
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#2
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Senior Member Group: Members Posts: 568 Joined: 26-September 10 From: Santa Cruz California Member No.: 12,218 Region Association: Northern California |
As I am finishing up new fuel lines, with clean, empty tank, it seems like the tank holds a slight pressure, when blowing thru the return line. I'll be using the bosch 044 fuel pump, which moves a lot of fuel, and want to make sure there is no pressure fighting the flow back to the tank. Does the stock '75 cap have any self venting property's, or does all the tank venting go thru the TINY vent port, that heads to the charcoal canister? If so, have any of you added a bigger vent, as a fuel cell would use? Thanks, Tom The gas tank vent is designed to prevent a vacuum from building up in the fuel system, and as a smog device to control gas vapors. If your tank is pressurized you have got a different problem to solve. Carbs are a low pressure fuel system; you should not have any pressure in the tank… |
tomrev |
Jan 11 2016, 06:22 PM
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#3
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Member Group: Members Posts: 231 Joined: 25-February 14 From: N. Mich. Member No.: 17,037 Region Association: None |
The gas tank vent is designed to prevent a vacuum from building up in the fuel system, and as a smog device to control gas vapors. If your tank is pressurized you have got a different problem to solve. Carbs are a low pressure fuel system; you should not have any pressure in the tank… This was based on my blowing thru the return line, into an empty tank, thru a -6 line. I think it builds a little back pressure because the vent tube is only about 1/16th in. diameter inside the tube. I will be running high pre. injection, not carbs. I suppose the pump is pulling more volume out of the tank, than the return line is putting in when running. Comparing it to a fuel cell, with a -6 (3/8 in.) ID vent line, where there is no resistance,it seemed odd. Will see how it runs. |
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