[Mike Hedger]

More times than not when you have this problem on a Q Jet the "main well plugs" in the bottom of the carb are leaking letting all of the fuel seap out of the carb and into the intake where it evaorates. To solve this pull the carb flip it over and take the baseplate off (dont forget to pull the back top long screws out first as they hold the rear of the baseplate) where you will find the plugs,(5 total but the 2 rear/bigger ones leak the most) clean them good with carb cleaner and a tooth brush. Take some JB weld or JB quick and seal them back up. I leave them upside down overnight to let it dry before I put fuel back in it. Hope this helps, Mike