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THE CENTRAL USA ROTAX independent Service Centre


independent Service Centre for ROTAX® AIRCRAFT ENGINES

Bing Carburetor Main Jet Conversion Chart

Bombardier Rotax has recently published an updated Bing Jet Chart and Main Jet conversion chart. All ultralights and light planes using ROTAX engines may want to verify what is in their carburetors versus the current recommendations. These new recommendations are a result of continued research and testing which allow the ROTAX engine to perform more efficiently and reliably throughout its power band.
    The „Bing Jet Chart Common Applicationš chart shows each engine and the stock carburetion setting at sea level. If you live other than at sea level or in a hotter climate, then you must refer to the Main Jet Conversion Chart to calibrate for altitude and temperature.
    Air density decreases with decreasing pressure and increasing temperature. If an engine is operated at higher elevation, the weight of the aspirated air decreases, whereas the aspirated fuel quantity remains practically the some. This results in richer fuel/air mixture than at lower sea level.
    If the engine is operated in high altitude for a longer period, it is necessary to adjust the carburetor calibration to re-establish the original composition of the fuel/air mixture. With increasing altitude (lower air pressure), the oxygen quantity sucked in by the engine decreases. The consequent loss in performance cannot be compensated for by different carburetor settings.
    To adjust the carburetor, in general a different main jet size is sufficient. Only in very particular cases a different needle jet and/or different idle jet also has to be installed.
    EXAMPLE: If a ROTAX 503 engine set up for sea level is shipped to Colorado Springs, Colorado, (approximate elevation 6,500 feet), the main jet would have to be changed. Our Bing Jet Chart shows the ROTAX 503 SCA (single carb, with a K & N Air Cleaner and without an intake silencer or after muffler) would have a main jet of 180 for sea level. By using the conversion chart, going to the approximate altitude of 6,500 feet and using the temperature of 50 degrees fahrenheit, you can see we have a multiplier of .95 and come up with our recommended jet of 171. This main jet will produce the same composition of air/fuel mixture that the 180 main jet would at sea level.

Temp
°F
Temp
°C
Altitude (meters)
0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000
Altitude (feet)
0 1,640 3,281 4,921 6,562 8,202 9,842 11,483 13,123
-22 -30 1.04 1.03 1.01 1.00 0.98 0.97 0.95 0.94 0.93
-4 -20 1.03 1.02 1.00 0.99 0.97 0.96 0.95 0.93 0.92
14 -10 1.02 1.01 0.99 0.98 0.96 0.95 0.94 0.92 0.91
32 0 1.01 1.00 0.98 0.97 0.95 0.94 0.93 0.91 0.90
50 10 1.00 0.99 0.97 0.96 0.95 0.93 0.92 0.91 0.89
59 15 1.00 0.99 0.97 0.96 0.94 0.93 0.92 0.90 0.89
68 20 1.00 0.98 0.97 0.95 0.94 0.93 0.91 0.90 0.88
86 30 0.99 0.97 0.96 0.94 0.93 0.92 0.90 0.89 0.88
104 40 0.98 0.96 0.95 0.94 0.92 0.91 0.90 0.88 0.87
122 50 0.97 0.95 0.94 0.93 0.92 0.90 0.89 0.88 0.86