Dude,
Don't waste money on a dyno when its probably spark plugs ! When were they changed last ?
You want heat range 5 plugs, gapping them at 0.8 mm overcomes some missing problems
If its not Spark plugs I would go Coils, havn't tried the yellowjacket ones.
http://www.skylinesaustralia.com/forums/Mi...500-t32356.html