It used to always start almost instantly but lately has been taking a little while to kick over and once it does it takes a second to clear it's throat and rev up. Doesn't matter if it is hot or cold. Once it revs up it runs like a top as it has always done. Once in a while it will just crank and crank and not start. So far it has eventually started on the second try. Any ideas? Since it runs great once running I am thinking it is something simple. Maybe a vacuum leak?