Question
Would you reccommend the use of a flamer to control weeds and other unwanted grass in a bermuda lawn?

Answer
Hubert:
I found these devices to be ineffective or wasteful of time. A mechanical approach may be most effective, if you are bound to methods without chemicals.
Johnson grass is a resilient foe.  I have fought it with a shovel and Roundup for decades.  In small populations of limited size, the shovel proved effective.  Dig up roots and dipose of them off the grounds or use your flamer to incinerate at this point.  The roots are white and approximately 1.4 inch in diameter and have nodes.
Roundup (or its equal) solution requires patience, persistence and exact timing.  All applications must be done at recommended rates before seeds form in mid to late summer.  Follow up applications should be done as soon as leaves appear again.
There are some additives for this plant which may be effective in combination with Roundup or another agent.  Check with your local ag agent about these.
This path will require years to combat Johnson grass.