If I'm not mistaken, that's the "lean burn stumble". If you have an MPGuino or a lean burn indicator, you'll see the correlation.
Learn to love it
- that's why you're getting the good MPG now.
I've only spent limited time in a lean burn Honda (Ben's VX engined CRX), so I found it a bit hard to notice. But Ben could identify the hiccup and knew when he was in lean land without needing to confirm on the fuel economy display.