There is definitely a loss of power when this occurs. Not that I keep my foot in the throttle very long. Sounds almost like http://www.youtube.com/watch?v=AEsFzeK0kB0 , just less rapid and a little louder. I have done a CASE relearn about once a week LOL. I have tried 9, 8 and 7 heat range plugs(NGK) since the rebuild. The 9's were first - I think it actually ran good on them until they became too fouled from a little street driving. 9's were recommended for my engine if running it to 20 psi. I lost the ground straps off a couple of 6's last year. The 6's are also a protruding style. I have been wondering about the plug gap as well. Although .025 is pretty well where the 7, 8 and 9's are gapped at out of the box. The 6's are around .035 out of the box.