Gentleman;
Thank you for your quick responses to my issues and your suggestions. Mr. Butler, I had a new spare thermocouple. I installed making sure the connections were tight.
Rich, I adjusted the air flow and that seems to have solved the blue/yellow flame issue. The sound now is loud but steady. I no longer have the sound I described in my initial letter, and there is not a noticeable difference with the door open or closed, just more muffled when closed. I made sure everything lined up. There is no evidence of soot buildup. The spark is set at 1/8th inch as specified.
After all this was checked, the unit fired approx 2 minutes. After waiting several minutes, it fired up for another minute or so. I might add that in all cases the water was warm at best inside the tank. Again I appreciate the suggestions and if my responses prompt any other ideas, they will be appreciated as well.
George