Step #1 - Assume Nothing!!! Check your carburetor(s) to verify the jetting
installed in the carburetor(s).Step #2 - Because air density varies with
temperature and altitude changes, a main jet correction may be necessary. This chart was
calculated at sea level with an air temperature of 60F.
Step #3 - Apply the multiplication factor shown to the main jet size recommended in
the chart at the top of the page.
Step #4 - Your operating conditions will vary by the change of seasons. If your
engine experiences performance difficulties, a review of your jetting may be necessary.
Return to step #2.
Step #5 - Humidity is also a variable in determining air density. A high humidity
means a lower air density of air to be consumed by combustion. Because we are generally
not equipped with a way of easily reading the % of humidity present, this can be read in
to this chart by adding altitude on high humidity days and subtracting altitude on in very
dry climates.
Create you base line jetting for standard conditions.
If your base line tuning was at 86 degrees and a 1500' altitude with a 155 Main Jet
Calculate Base Line: 155 Main Jet / .97 = 160 Base Line Jet or specifically 159.8
To correct for local conditions of 100 degrees and 4500' altitude
Calculate Corrected Jetting: 160 Base Line Jet x .94 = 150 Main jet to use
| Altitude - Feet |
0' |
1500' |
3000' |
4500' |
6000' |
| Temperature |
|
|
|
|
|
| -22F |
1.04 |
1.03 |
1.01 |
1.00 |
0.98 |
| -4F |
1.03 |
1.02 |
1.00 |
0.99 |
0.97 |
| 14F |
1.02 |
1.01 |
0.99 |
0.98 |
0.96 |
| 32F |
1.01 |
1.00 |
0.98 |
0.97 |
0.95 |
| 50F |
1.00 |
0.99 |
0.97 |
0.96 |
0.95 |
| 59F |
1.00 |
0.99 |
0.97 |
0.96 |
0.94 |
| 68F |
1.00 |
0.98 |
0.97 |
0.95 |
0.94 |
| 86F |
0.99 |
0.97 |
0.96 |
0.94 |
0.93 |
| 104F |
0.98 |
0.96 |
0.95 |
0.94 |
0.92 |
| 123F |
0.97 |
0.96 |
0.94 |
0.93 |
0.92 |
