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944Cup car build. What to do with Fuel tank venting

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Old 04-28-2010, 09:14 AM
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johntorg
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Default 944Cup car build. What to do with Fuel tank venting

I am rebuilding a race car roller for a friends son. I found that the fuel tank vent line, which formerly went to the carbon canister, now just ends under the car.

What should I do with it? I have the additional piece of hose/line that will bring it to the passenger fender well.
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Old 04-28-2010, 09:30 AM
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Gary R.
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Contact DanR. here, he had an issue with his vent I believe that was solved (or not)..
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Old 04-28-2010, 10:05 AM
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Originally Posted by johntorg View Post
I am rebuilding a race car roller for a friends son. I found that the fuel tank vent line, which formerly went to the carbon canister, now just ends under the car.

What should I do with it? I have the additional piece of hose/line that will bring it to the passenger fender well.
Perfect! Make sure that it can dump fuel right in front of the rear tire. That's what a shop did on my RSA when they installed a fuel cell. Took a couple of times to figure out why it got so loose on right hand corners when the tank was full.
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Old 04-28-2010, 10:41 AM
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I think Dan's just had a short line with a filter/vent on the end that fuel was dumping out of. I believe the fix was to put a longer line with a couple coils in it up higher? Have to ask him. Seems to me once the coils had gas in them the vent would be non-functional but maybe gas never gets that far..
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Old 04-28-2010, 11:12 AM
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I sent dan an e-mail and am waiting for a reply. In the meantime any other solutions?
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Old 04-28-2010, 02:33 PM
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Please post back with the solution as I am about to do the same thing

Thanks
Brian
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Old 04-28-2010, 03:41 PM
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The vent line goes from the top of the tank to the drivers front wheel well charcole canister. On the way it passes through a few things. There is a simple ball bearing check valve which shuts off flow if the car were "inverted." Then it goes into a small plastic expansion tank. A soft line drops from the expansion tank down under the car where it connects to a plast hard line. The hard line runs up into the engine compartment wehre it transitions yet again to soft line and connects to the canister.
The lines on top of the tank can get pinched and blocked. Beyond that it is fairly easy to trace the line, blow it out and keep it open.
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Old 04-29-2010, 12:08 AM
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On my Miata the tank vent incorporates a roll-over check valved which then routes to the charcoal canister. I ran a line from the check valve to a point away from the wheels and exhaust. I terminated the line with a simple mesh style fuel filter to keep out bugs from building a nest in the line and clogging it. I would think you could also rig a roll type valve for your tank vent fairly easily.
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Old 04-29-2010, 08:33 AM
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I'm pretty sure the rollover valve is located back at the tank. Pending a better solution, I guess I'll just add the line to the fender well and stick a filter on it.
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Old 04-29-2010, 08:53 AM
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On my 944Cup SP2 car, the previous owner had simply run the hose to the top of firewall on the driver's side, and capped it with a small K&N filter. Its apparently high enough that no fuel ever leaks out. Plus fumes are not an issue, as I guess air movement is slow.

I can tell you DO NOT cap that line. When I first got the car, I did have a problem with fuel fumes in the cabin. Tried different gas caps, checked seal of fuel level sending unit cap. Thought it might fill neck, until one very hot day at a DE when I discovered the tank would "exhale" strongly when the gas cap was removed. Plus I noticed the fumes got worse as the fuel level went down; not so bad with a full tank. So something was causing the tank to buildup a lot of pressure. Later discovered a portion of the vent tubing under the car had been crushed at some point. I replaced the crushed portion, and fumes inside were gone!

I believe that happens is that as fuel is oversupplied to the fuel injector rail, the return line goes back into the tank at a certain amount of pressure. The vent allows the tank to offgas and prevent any pressure buildup.
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