I have a free standing "B" vented LPG fireplace that has unusual flame characteristics. It is not a lifting flame however the yellow flame is way too tall and wispy, kind of dances around, in the process is hitting the glass causing sooting.Have tried air shutter adjustments to no avail. At times it will settle down and run normally but most of the time it seems to dance around. I wonder if it is venting properly? Any suggestions?