Once you know actual or absolute pressure, temperature and humidity you can identify the default mainjet. Use the Jetdial and follow steps A to C:

  1. Align actual or absolute pressure with temperature. Use white scales as shown below and assure accuracy before you proceed to the next step. Example:
  2. Instruction

  3. Hold disc in place.
  4. Go to humidity window. Default mainjet and clip position is indicated beneath the point where temperature and humidity intersect (30% humidity is halfway between the 20% and 40% line). Results:
  5. Instruction

  6. Warning: Read the Rotax manual and familiarize yourself with the engine and carburetor before working on your carburetor and using the Jetdial to change the mainjet setting and needle clip positions.
  7. Warning: It is imperative that you follow these instructions carefully. If the mainjet is too lean (low number), you can risk a piston seizure.
  8. Note: The jetdial delivers the default mainjet setting. Depending on whether you race on a long or short track, the setting may need to be adapted. In addition, every engine and carburetor has a slightly different response to weather factors, which needs to be taken into account by adding or deducting a correction factor (for instance, always go one mainjet size larger). However, on any given track and kart, the correction factor will be the same, regardless of the default setting you start with. Once the desired correction has been determined, the same correction can be used on any given day.
  9. Note: At lower temperatures, particularly below 40°F or 5°C, humidity is irrelevant. It doesn't matter whether the sun is shining or whether it's raining. The default setting solely depends on temperature and actual pressure. After aligning temperature with actual pressure, the red-white-red (0%) line in the humidity window indicates the default mainjet and needle clip position.
  10. Disclaimer: The developers, distributers and all parties associated with the Jetdial are not responsible for any damaged equipment, property or persons connected with the use of this product.