hi cb, I tried chinese ignition unit and genuine Honda tlr off a bike which ran well...still had the high rev misfire. Never did get to the bottom of it, but bike runs real good at normal trials revs, even good on big climbs, so never worried about it no more. been too busy building a house to pull the motor down, so just keep riding...and enjoying my trials.

Try with an easy test, install a new original Keihin #98 main jet, the one in the bike may have a smaller hole due to corrossion