On your EVO, not on a Pulsar? - I'm just going by what I was told last time mine was on the rolling road; the plug gap was too small (at 0.5mm), and making it bigger fixed the problem. Maybe I've gone too far the other way and missed the sweet spot?
Surely the larger the gap, the bigger the potential you need to jump it so it's a larger/more powerful spark.
If the gap is too large the spark can't jump and you get a missfire (especially under boost when the effective plug gap is much greater due to the compressed air-fuel mixture).