REJETTING FOR ELEVATION AND TEMPERATURE
THIS INFORMATION IS A GENERAL GUIDELINE, YOUR
RESULTS MAY DIFFER.

When rejetting for elevation change it is also important to keep in mind temperature variation as well. To calculate the a new jet size use the tables below:

ELEVATION CHANGE
  FROM LOW GOING TO HIGHER   FROM HIGH GOING TO LOWER
ELEVATION FEET 8000 7000 6000 5000 4000 3000 2000 1000 0 -1000 -2000 -3000 -4000 -5000 -6000 -7000 -8000
N100.604 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8
N102/221 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8
4/042 -48 -42 -36 -30 -24 -18 -12 -6 0 6 12 18 24 30 36 42 48

 

TEMPERATURE CHANGE
°F 60° 50° 40° 30° 20° 10° 0° -10° -20° -30° -40° -50° -60°
N100.604 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6
N102/221 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6
4/042 -24 -20 -16 -12 -8 -4 0 4 8 12 16 20 24

 

EXAMPLE:
Main jet is mikuni type 4/042 size 200. Current conditions 1000 feet elevation at 70° deg; F. New condition will be 8000 feet and 60° F. What jet size is needed?

SOLUTION:
1. Start with the elevation change of 7000 feet (8000-1000=7000). Look at chart for 4/042 and 7000 feet (going up in altitude from 1000 to 7000 feet so altitude change is positive) chart number is "-42".

2. Next correct for temperature change, 70°-60°=10°. Since the temperature is dropping -10°, chart number is "4".

3. Add the two numbers together: -42+4= -38. The main jet needs to go down by "-38" therefore the jet needed is 200-38 = 162.

4. Choose the nearest jet sizes to this number, in this case 160. It is beneficial to purchase a larger and smaller jet as the calculation is an approximation. Several sizes to try would be 160, 162.5 and 165. As always read the plugs to confirm the jetting is correct.

Here is a link to identify your jet