I have four Drone BB diesels. Run with stock fixed compression head and variable compression head. Ran fixed compression many times but one day with temps in the low 40's F. could not get it started. Ran with variable compression with temps in the 30's F. with no problem. A vibrator and have flown on a full size Playboy Cabin. My GB 5.4 cc diesel less vibrations so more fun on the Playboy or Airborn 810 sq. in. wing area. Jack