Number 8 Exhaust Valve sticking

[djuby1]

This summer the the No. 8 exhaust valve started sticking while going down the road on several tours this past summer. The problem is intermittent but seems to be happening more each time and stays stuck longer. I use Marvel oil additive in the gas and I use zero ethanol gas. Several buddies have suggested spraying a lacquer remover into the No 4 cylinder to remove the varnish on the exhaust valve. Has anybody had this issue and what was your remedy for the sticking valve?