If it runs only with the choke out, it may also mean you have a jet or passage partially plugged in the carb. As directed above, try the propane trick to see if you can find a vacuum leak. I would also suspect a piece of something in the carb if you just had it all apart.
a gasket above and below the insulator should be ok. Remember, a gasket is supposed to be softer than what it is placed against and help to seal minor surface imperfections.
