Quote:
Originally Posted by bluesideup
I've operated a C-35 Bonanza for 400 hours. It has a pressure caraburetor. I' ve not found any special prolems or techiniques necessary to operate it. After shutdown its a good idea to store the airplane with the mixture rich and the trottle almost all the way in (towards the full throttle position). This allows a little fuel to drip into the carburetor to keep the diaphragms moist. They cost about $1700 + labor to replace. Some also suggest bringing th fuel pressure up with the electric pump after shut down to inhance the effect.
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Fully understanding the inner workings of one of these beasts would help to make it clear that leaving the mixture rich or lean does not affect whether there is fuel in the regulator. In other words, there will be no advantage leaving the mixture rich or lean or leaving the throttle open or closed.
What goes bad in these carbs is the diaphrams. Running the engine regularly is the best insurance for keeping them elastic.
The throttle has no effect on the diaphrams when the engine isn't running. (One exception being that when at full-idle position, the throttle linkage pulls the idle valve into a leaner position)
The mixture control, when full lean, depresses a spring in the fuel regulator which removes the spring tension from the air-metering diaphram, thus allowing the fuel metering poppet valve to fully close, stopping all fuel flow to the discharge nozzle. This diaphram isn't in contact with fuel and isn't as prone to getting stiff as the outer diaphram. Bottom line, rich or lean mixture won't change the amount of residual fuel left in the carb chambers nor will throttle position.
Once the fuel pressure drops off at shut-down, the discharge valve closes and the fuel that is in the carb is trapped. The only way to
maintain "wetness" (assuming that the carb leaks down) is to periodically run the engine or pressurize the carb with the wobble pump or boost pump.
They are weird pieces of machinery and few people have experience with their inner workings.
