> Paul M. Anton wrote: > Hello All: > When I purchased my 'Coupe the mixture knob was wired full > rich. I asked the previous owner about it and he said that the AI > required it when he did the annual. The plane has the Stromberg > carburetor. Can someone fill me in on why this was > done? If the > mixture control is not to be used, why is it there? > ==============================================================
The design of the Stromberg is somewhat self compensating, i.e. the mixture stays more nearly correct over a wider range of altitudes (than the Marvel). On many planes of the era, the mixture control was an option. Those that didn't have it were wired in the full rich position. I'm also told that, since many of these planes were used as trainers, there was some feeling that they were safer wired full rich. There are a number of different mixture control arms available, many of which only require about an inch of "pull" from full rich to full lean. And it *will* kill the engine at cruise, especially at low altitudes. This proved too sensitive for many student pilots. With the passage of time, and lack of use, many of these mixture controls are no longer effective. If the two plates are scored, as many are, there is too much leakage for it to work. Also, there are shaft seals that have deteriorated over the years that cause leaks. Since the mechanism works by applying suction form the carb throat to the float chamber, any uncontrolled leakage will reduce the effectiveness. I did an AD search on the various 'coupes, strombergs and continental a and c series engines. I could find no AD that mandate wiring it in the full rich position and I am confident that none exist. There may have been a service bulletin suggesting it at one time or another, but I don't know of one. John
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