Working on my portable BBQ for camping. Last night using it , it would not go over 200 degrees. Cleaned it all up, checked all burner holes for obstruction and they are good. Blew all lines out. Sometimes if you start it on full heat it makes a whooshing or whistling sound? You shut it off, turn heat down and it is fine on the restart. Back set of burner holes don't start for awhile at full heat but then come on a bit later. Regulator? Anyone know?