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Rotax Max 125cc Jetting - Simple Version PDF  | Print |  E-mail
Written by Vic R   

To achieve maximum power in a Rotax, the correct main jet is required.  The challend is that temperature, humidity and air pressure all infuence the choice of jet.  A simple way to determine an appropriate main jet is to consider the clothes worn by spectators or your crew.  


 Clothing worn by crew
Jumper or jacket
Long pants and shirt
Shorts and T-shirt
Shorts (feel uncomfortable because of heat)
  • The Jets in the table assume the track is a sea level
  • Reduce Jet size for every 500 metres above sea level.  (e.g. at 1000m, if 168 should be the correct jet based on the table above, use a 162 instead)

Incorrect jetting will result in engine backfire.  DO NOTcontinue to drive if the engine backfires as damage will result.

  • Backfire at the end of the straight is generally caused by using a Jet that is too lean (Main jet nunmber is too low).
  • Backfire out of corners is generally caused by using a Jet that is to Rich (Main jet number is too high).