Tim, mine was off by more than 10 degs from the factory.  It was set at 39 degs. and would not idle right nor transition very well.  It would sometimes be sounding OK then just pop and die.  I played with carb settings for days trying to get it right.  Having worked as an engine tech since I was 9, (I am now 53 and still bending wrenches) I started looking for problems and found the timing issue.  I had to make some mods but managed to get my timing back to 28 degs and WOW what an awesome little motor it became.  It will now idle all day long at 1100 rpm's and transitions with the best.  Yes timing does make a difference and it's not up at full throttle as I neither gained nor lost a single rpm at full throttle after the change. (I use a tach to check my high speed needle adjustment)

P.S. It did make it start much easier.