That looks familiar! Just went through a similar situation this summer. Mine did not back fire but sounded like light pinging or valve float. The rocker beat the valve spring retainer so bad it barley held the spring. Could have destroyed my original block in a heartbeat. Dodged that bullet. Improper cam break-in will round a lobe pretty quickly. Make sure you follow the cam manufacturers break-in procedure or you'll be right back where you started. Good luck
