How long before you can start it again? When this happens, you need to determine if you are getting spark or not. If you are, chances are it's fuel system related; could be vapour lock. Test for spark with a spark tester (enclosed for marine). Or hook up a timing light; it's a quick although not as accurate way to tell if you are getting a spark. If you're going to remove a plug to check for spark, be aware that it's an open spark in a bilge so be safe, ventilate and ensure there are no lingering vapours. Let's eliminate one system at a time and go from there. Let us know what you find.