If your bolts and gasket were properly installed to Yamaha's specs. You shouldn't find any leaks.
Over tightening the bolts will get it to pass the leakdown test, but will later on cause more problems.
If you find a leak coming from the cases, then you will have to take it back apart. (Your leakdown SHOULD be done with both side covers off. That way you can see if you have a case leak.) If the leak is in your intakes, you might get away with some RTV. If the leak is in your tester (Very common), just use some more Yamabond to seal the caps.
So, I guess to answer the question...It depends on where the leak is.