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Old 03-13-2010, 09:58 PM   #1
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Default gas tank vent

what do you do with your gas tank vent line after you have gutten all of the emmisions crap???
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Old 03-13-2010, 10:39 PM   #2
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In for answer. I took mine off and after a session on track, it was puking fuel. Coupled with my boiling coolant (royal purple's water wetter does NOT raise the boiling point of water), and leak oil pan, I was leaking all fluids but the brake fluid. I've fixed those last two, but I need to do something about that vent line. I saw on cr.net that they plumb it back into the hose barb on the subframe, but Then it would just puke from there, wouldn't it?
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Old 03-14-2010, 03:03 AM   #3
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If you recall, the charcoal canister has a line going to a hole in the chassis. When I removed the charcoal canister, I simply put the rubber hose that was connected to the chassis to the vent line.

My fuel tank still seems to hold pressure, even though there is a open vent line. I am not sure I know what is preventing gas and fumes from going out of the vent line, unless it is sealed by the fuel cap.
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Old 03-14-2010, 03:21 AM   #4
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Yes that is what I discussed. However in race conditions, especially when hot, the tank seems to build excess pressure. That is what I'm worried about, as the hole in the chassis seems to be VTA. Have you raced this "solution"?
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Old 03-14-2010, 06:24 AM   #5
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where is this hole located?? i dont see how fuel is gonna travel back a vent line, it should be located near the top of the tank. unless you had a full tank with alot of fuel slosh
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Old 03-14-2010, 10:36 AM   #6
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When I open the fuel cap, you can tell that there is pressure. It made me think that the vent is linked to the filler neck some how. I will have to look and see what else I did to keep fuel from evaporating out. It has been over 10 years since I did it.
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Old 03-14-2010, 02:22 PM   #7
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im told that i can just cap it
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Old 03-14-2010, 06:00 PM   #8
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put a small piece of pipe between the two lines
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Old 03-14-2010, 06:09 PM   #9
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Again, that hose barb on the subframe seems to be VTA, how is it going to prevent fuel puking. If not, does anyone know what it is?
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Old 03-15-2010, 07:31 AM   #10
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never has on mine try it see what happens
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Old 03-15-2010, 08:47 AM   #11
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Quote:
Originally Posted by curly View Post
Yes that is what I discussed. However in race conditions, especially when hot, the tank seems to build excess pressure. That is what I'm worried about, as the hole in the chassis seems to be VTA. Have you raced this "solution"?
You don't have your exhaust heating the tank, do you?
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Old 03-15-2010, 01:46 PM   #12
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That line is the fuel tank vent - a bad idea to cap it. If it is puking a LOT of fuel, something is wrong in the tank - quite possibly the purge solenoid or one of the check valves needs replaced. The fuel tank will hold a little bit of pressure in it, this line is meant to keep the pressure from going too high. The fuel tank pickup point for this line is at the top of the tank, so any fuel that comes out of this hose should only be fuel vapors, not liquid gasoline unless it has collected as condensation inside the lines which would end up as a very slow drip instead of a fast 'puking fuel'. One definite possibility which may lead to the 'puking fuel' condition is overfilling the fuel tank - don't do this. The 'correct' way to delete the charcoal canister is to simply run a rubber hose between the hardline coming from the fuel tank, and the hardline which drops down into the subframe area and exits to atmosphere. I believe the hose that comes off the fuel tank hard line is ideal for this bypass.
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Old 03-15-2010, 09:22 PM   #13
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On my N/A Miata, I routed the vent line to the fitting in the subframe. On the turbo Miata, I have it capped. I've never had a problem with either through rigorous autocross use. The fuel tank builds pressure (I haven't confirmed if it's positive or negative pressure) no differently than the stock setup with working emissions equipment in place.
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