Have done the tappets and tried polishing the CV (carb) slide whilst I could get at it but it didn't make a lot of difference as the slide itself is coated in a black substance, me thinks maybe teflon. I oiled the slide once more and again cured the missfire but it's already appearing again. The only long lasting cure is possibly to remove the carb itself and polish the inside of the slide barrel to hopefully remove any rough edges. All the best, Pat