ALL LP refers have a spiral baffle that hangs inside the burner flue just inside the tube above the flame. The purpose is to distribute the Heat from the flame evenly to Heat the fluid. After 30/40 years that baffle has probably rusted/burned up a part of it and a piece fell down on the burner. Look at this link and you will see a picture of this baffle. Now, usually this part is NOT available
You have to find one i n a throwaway refer or build your own. These are from my OLD notes. Doug
From my notes for the RM763-
WIRE LENGTH IS 25-1/2"
BAFFLE LENGTH IS 5-7/8"
TOTAL LENGTH 31-1/4"
BAFFLE WIDTH IS 3/4"
https://escapees.com/rv-refrigerator-part-2-lp-gas-operation/