Here's some interesting info on the Bing Carbs
Technical Information For bing carburetor Adjusting the Bing Carburetor - The Bing Carburetor has a three stage system: Idle, Midrange and Top End. Idler Jets - From the moment the engine is started to approximately 1/4 throttle, the carburetor is running according to how the idle system is set up. As the idler jet number decreases, the mixture gets leaner as the number increases, the mixture gets richer. For instance, Idler Jet #45 has a leaner mixture than Idler Jet #50 The Air Regulating Screw must be set as stated in the Bing Jet Chart in order to insure smooth operation of the Idler Jet. This screw adjusts the air/fuel mixture at idle speeds and for smooth acceleration. Turning the screw in a clockwise direction creates a richer mixture while turning it counterclockwise creates a leaner mixture. To adjust this screw, gently turn in a clockwise direction until the screw bottoms out, then loosen the screw (in a counterclockwise direction) the number of turns as recommended in the Bing Jet Chart. (effective range 1/2 to 2-1/2 turns out). Use the carburetor piston Adjusting Screw to adjust the idle RPM. Turn this screw in a counterclockwise direction until the Carburetor Piston is in the lowest position. Then carefully turn the screw clockwise until it just engages the piston and then continue to turn it clockwise for 2 to 2-1/2 turns. This determines the idle RPM. of the engine and should be set at 2,000 RPM min. Needle Jets/Jet Needles - The Jet Needle has three or four grooves which the clip can be snapped onto. The grooves are 1, 2, 3, 4 with number 1 at the top position . When the clip is snapped onto the top position #1 of the needle, a leaner mixture is created than if it was mounted on the #2 groove. NOT: Jet Needle clip must always be under plastic spring cup. The Midrange System affects the carburetor for approximately 1/4 to 3/4 throttle. Once again, the lower the needle number of the Needle Jet, the leaner the mixture. Main Jet Conversion Chart - The Jet chart shows each engine and the stock caburetion 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, where as the aspirated fuel quantity remains practically the same. This results in richer fuel/air mixture than the 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 injested 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 does a different needle jet and/or different idle jet have to be installed. Example: If a single carb 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. The carburetor would have a main jet of 180 at sea level. By using the conversion chart, going to the approximate altitude of 6,500 feet and using the temperature of 32 degrees, you can see we have a multiplier of .95 and come up with a 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
Technical Information For bing carburetor Adjusting the Bing Carburetor - The Bing Carburetor has a three stage system: Idle, Midrange and Top End. Idler Jets - From the moment the engine is started to approximately 1/4 throttle, the carburetor is running according to how the idle system is set up. As the idler jet number decreases, the mixture gets leaner as the number increases, the mixture gets richer. For instance, Idler Jet #45 has a leaner mixture than Idler Jet #50 The Air Regulating Screw must be set as stated in the Bing Jet Chart in order to insure smooth operation of the Idler Jet. This screw adjusts the air/fuel mixture at idle speeds and for smooth acceleration. Turning the screw in a clockwise direction creates a richer mixture while turning it counterclockwise creates a leaner mixture. To adjust this screw, gently turn in a clockwise direction until the screw bottoms out, then loosen the screw (in a counterclockwise direction) the number of turns as recommended in the Bing Jet Chart. (effective range 1/2 to 2-1/2 turns out). Use the carburetor piston Adjusting Screw to adjust the idle RPM. Turn this screw in a counterclockwise direction until the Carburetor Piston is in the lowest position. Then carefully turn the screw clockwise until it just engages the piston and then continue to turn it clockwise for 2 to 2-1/2 turns. This determines the idle RPM. of the engine and should be set at 2,000 RPM min. Needle Jets/Jet Needles - The Jet Needle has three or four grooves which the clip can be snapped onto. The grooves are 1, 2, 3, 4 with number 1 at the top position . When the clip is snapped onto the top position #1 of the needle, a leaner mixture is created than if it was mounted on the #2 groove. NOT: Jet Needle clip must always be under plastic spring cup. The Midrange System affects the carburetor for approximately 1/4 to 3/4 throttle. Once again, the lower the needle number of the Needle Jet, the leaner the mixture. Main Jet Conversion Chart - The Jet chart shows each engine and the stock caburetion 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, where as the aspirated fuel quantity remains practically the same. This results in richer fuel/air mixture than the 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 injested 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 does a different needle jet and/or different idle jet have to be installed. Example: If a single carb 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. The carburetor would have a main jet of 180 at sea level. By using the conversion chart, going to the approximate altitude of 6,500 feet and using the temperature of 32 degrees, you can see we have a multiplier of .95 and come up with a 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