George, if you are still using the same spark plug then maybe time for a new one or try freshening up the one you have. There's a couple of vids on youtube about that procedure. Also, with that mileage you're kind of at the tail end of your break in period. So you could try moving the needle clip up one notch to lean it out a bit as your engine is maturing to adulthood, or possibly even down a notch. As the rings set in they provide more compression ie power so you may be feeling that stage a little more.
And, like Agreen said, check the plug colour and that will tell you what she's doing and what she might need. That's really the first thing to look at before doing anything else.
Are you still running a break in oil ratio?
