When running your 900 without the tank you must plug off the small nipple/vaccum port to the 3rd carb. the small line that goes to that nipple is the primer for the pet cock. if that hose is not plugged it will not start you may have to prime the motor through that nipple. the other hose is a vent for the gas tank. you dont need to worry about that one. so use a lawnmower gas tank with a fuel line to carb plug the small nipple on the carb it should then start right up i have run mine like that many times. the bike runs better with all lines hooked up correctly to tank. so if it does run a little ruff its b/c u dont have the tank on