Remove reed valves and poke the feeler gauge in there. You're looking for a max clearance of 0.85mm according to Honda. I think that over 0.7mm is getting a bit close, even though that's within the standard spec.

Measuring the end clearences will only tell you some of the story though. Crank out is better.

Tik tik tik........may be your RC valves? Had this before with worn shafts.