Sunday, April 9, 2017

Bing 64 (CV) Carburetor Part 3 (Idle Circuit) Sport Aviation / Experimenter "Technically Speaking" Article March 2017

Bing 64 (CV) Carburetor Part 3  (Idle Circuit)

March 2017 Sport Aviation Magazine

In Part 2 of this article, we talked about the starting carburetor (choke) system. We can run the engine at lower RPM settings only on the choke system, but as soon as we reset the choke system to the off position, the engine is now running on the idle circuit only. We often use this as a troubleshooting exercise. If the engine runs with the choke partially on, but dies as the choke is placed in the off position, it is an indication that the idle circuit is the culprit. It is absolutely essential that the idle circuit be set up and functioning properly. We use the idle circuit on every flight, and it is a surprisingly important system within the carburetor. Aside from the practical aspects of having a properly operating idle circuit, there are many correlations with the idle circuit malfunctioning and other engine problems, ranging from increased maintenance to engine stoppage and even engine failure.
If you follow our articles on a regular basis, you already have an insight into our underling premise that all successful troubleshooting, maintenance, and operation, comes as a result of  a solid foundation of the theory and physics surrounding the subject matter. With that being said, let’s dig into the theory of the Idle circuit.
With the slide (piston) completely closed, the vacuum present at the main fuel outlet is not sufficient to draw the fuel up from the main jet, through the mixing tube, needle jet, and into the diffuser and throat of the carburetor. At low power settings we need to supplement the fuel air system with an auxiliary fuel-air system consisting of an idling air jet, Idle jet, bypass, idle outlet bore, and an idle mixture screw. (Figure: 1)
Figure 1

Saturday, April 1, 2017

Bing 64 (CV) Carburetor Part 2 (Starting Carb) Sport Aviation / Experimenter "Technically Speaking" Article February 2017

Bing 64 (CV) Carburetor Part 2  (Starting Carb)

In Part 1, we examined the basic principals of operation of  the CV (Constant Velocity) carburetor. In this article we will take an in depth look into one of the most misunderstood subsystems of the carburetor, the “Starting Carb”.  It is often referred to as the “choke”, however, this  doesn’t properly describe the operation of the Starting Carb.  A choke is, really, a valve on the inlet side of a carburetor used to restrict the flow of air through the carburetor. This results in a low pressure with the intake manifold and carburetor system as a whole. This is different from the carburetor butterfly valve which is located down stream from the fuel nozzle which also restricts the airflow creating a low pressure, but only within the intake manifold. The choke valve which is located before the fuel nozzle presents a low pressure to the entire carb. This low pressure, naturally draws more fuel through the carb and into the intake manifold resulting in an enriched mixture. The starting carburetor, on the other hand, is in fact a separate carburetor within the larger carburetor. This starting carb provides for an enriched mixture by introducing addition fuel as well as air during the starting sequence. The starting carb on the CV carb is different from that incorporated into the slide type carburetors used on the Rotax 2 stroke engines. The (Bing 54) carburetors, used on the 2 stroke engines also use a starting carb, but it operates in an On/Off capacity. On the CV carb the starting carb operation is adjustable allowing for full application during start and cold weather operations, and the ability to reposition the “choke” for less affect as the engine warms.
Figure 1