Visit B&S's website and it look up your engine IPL(illustrated parts list) then you should be able to see which is which.
http://shop.briggsandstratton.com/BShopProductListingPage.asp?MECID=100&LRID=2&CATALOGID=56B2B9A7-283C-11D4-8886-00B0D0203414
From an illustration of the 4 stroke cycle in the manual it shows that the intake closer to the output end of the crankshaft, however best to check with the IPL.
William
August 2006