it's pretty common on any bike if you've got a poor gasket.
if gaskets arent sealing it may not be flat or it may be gouged. if so, you can fill in and smoot out gouges with JB, and you can wet sand the mating face - at least on the intake piece itself - to get it smooth and flat.
if you use silicone sealer, try to find something gas resistant.
another final not, be sure your bolts are tightening down all the way. you may need washers because where you think it's getting tight it may just be bottoming out the studs and not really pressing the intake on tightly.