I'm having a stall issue.  My bike is a 2002.  It was running perfectly until a girl pulled out in front of me and I laid it down pretty hard.  Immediately when I got home I noticed a bit of oil on the cylinder head.  Since then the bike will run fine for about 10 minutes then as I'm downshifting to come to a stop it will backfire and stall if I pull the throttle during this it bogs down like it's not getting any gas.  After this the bike will not start for around 10 minutes.  I changed to a new petcock already and am about to clean the carb.  Any ideas before I get into the carb?

Thanks!  Main was dirty, cleaned the entire carb.  Running better than ever.