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Bing Carburetor Technical Information

Adjusting the Bing Carburetor
The Bing Carburetor (36mm) is a three stage system: Idle, Midrange, and Top End System. From the moment the engine is started to approximately 1/4 throttle, the carburetor is running according to how the ldle System is set up. As the idler jet number decreases, the mixture gets leaner; (see part# 4), as the number increases, the mixture gets richer. For instance, ldler Jet #45 has a leaner mixture than ldler Jet #50.
ldler Jets
     The Air Regulating Screw (see part# 10) must be set as stated in the Bing Jet Chart in order to insure smooth operation of the ldler Jet. This screw adjusts the air/fuel mixture at idle speeds and for smooth acceleration. Turning this 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 counter-clockwise direction) the number of turns as recommended in the Bing Jet Chart. For example, the ROTAX 503A would be .5 (1/2 turn) out (effective range 1/2 to 2-1/2 turns out).
      Use the carburetor piston Adjusting Screw (see part# 11) to adjust the idle RPM. Turn this screw in a counter-clockwise direction until the Carburetor Piston (see part# 3) is in the lowest position. Then carefully turn the screw clockwise until it just engages the piston and then continue to turn it clockwise for2 to 2-1/2 full turns. This determines the idle RPM of the engine and should be set at 2,000 RPM.
      The Midrange System affects the carburetor for approximately 1/4 to 3/4 throttle. Once again, the lower the number of the Needle Jet, the leaner the mixture.

Needle Jets, Jet Needles
(NOTE: Jet needle must always be under plastic spring cup)
The Jet Needle (see part# 2) has three grooves which the Holding Plate (see part# 3) can be snapped onto. The three grooves are numbered 1. 2, and 3 with number 1 in the top position (note: some jet needles have 4 grooves as in diagram #1 at right). When the Holding Plate (see part# 3); is snapped onto the top position (#1) of the jet needle, a leaner mixture is created than if it were mounted in the #2 groove.
  1. lnstall sieve sleeve by slightly squeezing it by pushing it all the way up the mixing tube.
  2. Smaller numbers indicate decreasing jet opening and leaner conditions.
  3. The #54 marked on the side of the carb is just a casting mark.
  4. Float guide pins should be polished to insure smooth float action.
  5. Floats with aluminum guides should be replaced.
  6. lnspect jet needle grooves for wear every 50 hours.
  7. Float arm should start out parallel to the float chamber base.
  8. Fuel pump must be in system to insure correct fuel level.

How to Check the Float Level
  1. Start and warm up engine.
  2. Run the engine at 3/4 power for 2 minutes.
  3. Let engine idle back and cool down for 1 minute.
  4. Shut off engine and fuel system (if the fuel system is an overhead system).
  5. Remove float bowl.
  6. Remove the floats from the float bowl while float bowl is sitting on a level surface.
  7. The fuel level should measure approximately 1/2" from the top edge of the floatbowl.
Fuel level below 1/2" will cause a lean mixture.
Fuel level above 1/2" will cause a rich mixture.

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