View single post by Jim Ketcham
 Posted: 10-31-2006 12:11 am
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Jim Ketcham


Joined: 03-13-2005
Location: Salt Point, New York USA
Posts: 208
I don't quite agree with the advice given above for your new tank installation. 

I believe clarification of the function of each line is in order for you to make a decision on whether to eliminate it or use it.

The top line out of the cap on the top of the tank is a pressure relief line.  The cap is a pressure relief valve and is a safety item.

The line that attaches to the rear most port on the tower on the top of the tank runs to the carbon canister.  Its function is to direct evaporative hydrocarbon emissions to the charcoal canister when the car is sitting in the sun or warmed and the fuel vaporizes.  When working correctly, the hydrocarbons are then sucked back into the carbs and burned when you start the car, thus purging the canister for next time.  It is one of the few emission devices that does not rob your engine of performance and really is good for the enviornment.  If you decide to not use the carbon canister and vent these vapors to the atmosphere, just make sure it is done away from a source of ignition (not under the hood).

The second line that attaches to the top of the tank is NOT a return line.  It is an antisyphon line.  It has an internal check valve that prohibits flow from the pump outlet to the tank (thus not a return line).  It allows air (vapor) to be drawn in to the line to the carbs if the pump is not running and a syphon forms if the carbs are lower than the fuel in the tank.  It is a safety feature, that I understand, was added after car fires in vehicles parked downhill.