Airplane Light Sport Aircraft ROTAX Engine 912: Fuel

Best fuel to use for your Airplane Light Sport Aircraft ROTAX engine is unleaded auto gas, premium (91 octane) for 100 HP 912S and 115 HP 914 turbo, but regular (87 octane) is OK for 81 HP 912.

AVGAS can be used but special considerations are needed (see details below)

Auto Gas/Alcohol

  • Auto gas with up to 10% alcohol tested and approved by ROTAX. However, the airframe manufacturer must approve the 10% for the fuel delivery system.


  • Can use AVGAS, but lots of lead in 100LL, so special considerations are recommended when using primarily AVGAS.
  • Cross country must use 100LL because it is at airports, but plan and SHELL AeroShell Sport Plus 4 primarily AVGAS.
  • Oil changes are required sooner with AVGAS IMPORTANT NOTE: See for current recommended oil change intervals/updates – Mainly (greater than 30% AVGAS) 50 hours oil change intervals – Primarily (greater than 50% AVGAS) use 25 hours oil change intervals
  • Continuing use of 100LL, low power settings, not using TCP can result in excessive lead buildup on the valves. This can result in an occasional miss after about 400 hours under these adverse conditions.
  • With 100LL use, take oil tank out of aircraft and clean tank regularly (at least once a year or every 100 hours) to make sure lead does not build up in bottom of tank.


  • AVGAS stores well, fill up if you are going to store.
  • Auto gas with stabilizer can also be used for storage.
  • Before storage, run engine so AVGAS or auto-gas with stabilizer will run through carburetors. Gunked up carburetors are typical from storage which is easy to avoid.

Hight Altitudes

  • AVGAS is more stable at higher altitudes and less chance to create vapor lock (boil) at lower pressures/higher altitudes. Insolated fuel lines are also recommended if inside enclosed engine compartment to lessen the chance of vapor lock.

Fuel Filters

  • Use 0.1 mm (.004 inch) mesh metal fuel filters
  • Do NOT use paper (which is typically white) because it absorbs water and can stop the fuel flow
    because of finer filtration than needed and it is more susceptible to blockage.
  • Do not use plastic fuel filter inside enclosed engine compartments (a metal gascolator is recommended).