bike will only run with the gas tank off ? Help

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LOL Man this one had me going for a bit. Should have read the last posts first!

OK, so the little vent hose that comes out of the front of the tank and down to the canister is part of the California Emission System. It's meant to keep excess vapor from the tank from going out to atmosphere by including it in the air circulation of the vacuum lines to the carbs. When the bike is running, no vent from the tank to open air basically. There is no actual pressurization of the fuel tank as there is always an open line from the tank (right rear quarter of the tank area underneath) which vents out to behind your right foot peg.