• Log. Keep notes during break-in; include run time rpm and any special details for each run.
  • Fuel. Use the highest nitromethane content recommended by the engine's manufacturer - usually between 5 and 15 percent.  Lubrication content should be 20 percent. Use some castor oil.
  • Muffler. The engine will run cooler if the muffler is removed for break-in; however, you'll lose the solid needle-setting muffler-pressure advantage.
  • Propeller. Use one that is smaller than the recommended flight size, e.g. 12x6 for flight; 12x5 for break-in.  Air cooled 2-stroke engines run cooler when the load is reduced.
  • Procedure
  1. Set the needle valve for a 2-cyclyling start (see engine owner's manual).
  2. Start engine; if necessary, leave the glow heat turned on to keep the engine running.
  3. Adjust the needle valve for a rich, 2-cycling operation.
  4. Run for approximately1 minute.
  5. Perform step 4 four to six times with cooling-off periods between.
  6. Run the engine for 3-minute periods, rich 2-cycling as before.  Cool completely between runs. Perform five to eight times.
  7. Start the engine.  Allow it to warm for at least 20 seconds.  Lean the high-speed needle valve until the engine peaks (attains maximum speed) as determined by a tachometer.  Back off (richen) 200 to 300 rpm.  Check this setting by pinching the fuel line while you watch the tachometer; rpm should increase by 200 - 300 rpm and then return to the original rpm.  Listen to the engine closely and watch the tachometer.  If the engine begins to slow, quickly richen the needle valve to the rich  2-cycling position of step 6, as the engine needs more running time.
  8. The engine should hold its semi-peak setting for at least 30 seconds without losing speed.  If the engine still doesn't maintain rpm, richen the mixture and run through step 6 again.
Remember that the break-in process requires relatively short engine runs during which cycling heating and cooling relieves stresses within the engine components.  ABC-type engines usually take 30 - 45 minutes to break in.