It is necessary that you take proper care when assembling the intake tube and flange as part of an intake gasket change.  There is a lip on the cylinder end of the intake tube that recesses into the flange.  It sits a bit proud of the flange so the the intake gasket will get a good seal.  Before you tighten the intake make sure that the tube is recessed in the flange.

Here are a few pictures to guide you through.

Cheers

Roscoe
Yankee-Aviation.com
513-519-7008