Massey, The problem that I have found with the 4 heaters that I run that caused the same fault that you had, running a few minutes then trips the buzzer. The only thing that I have found that fixed the problem was adjust the flame detector so that it can 'see' straight down the tube. All 4 of mine came to me without functioning properly, I did the same as you.... adjust injector and spark, still couldnt make them run, until I, by accident pulled the flame detector tube from the burner manifold, it had a very small bend. I bent it straight and southern engineered the sensor to 'see' and stay straight with the tube.... voila, problem solved. No guarantees that would be your fix, but I spend ALOT of hours trying to get mine to work, and that was the only thing that fixed it.
The reasoning behind the hour meters being disconnected is addressed in the manual... TM-5-4520-256-14. page 3-16.4
"If the failure was in the R1 rectifier or TT hour meter, the heater will now operate in this manner. Ifmalfunction still exists, notify Direct Support Maintenance.
Rectifier and hour meter are not required for Army use and should be left disconnected."