QUESTION: I operate a IO-540C4-B5 in an experimental. I am wondering about the correct position of the mixture lever after idle cutoff has been selected. Should I leave the lever in that position, or should I advance it (after the ignition is switched off) to full rich? Is there any benefit to the internals of the servo to leave the lever in one position or another from flight to flight?
ANSWER: David, it makes no difference where you leave the mixture control after you’ve shut the engine down using the idle cut-off. I think most will agree it is usually left in the idle cut-off position following engine shutdown.
Many years ago when the pressure carburetor was used on some applications, it was recommended to return the mixture control to the full rich position following shutdown because the diaphragm in the throttle control had a tendency to take a set. There was a chance that, if the mixture was left in the idle cut-off position, you wouldn’t get the engine started. Fortunately, technology has allowed us to move beyond some of those unique recommendations.
Paul McBride, recognized worldwide as an expert on engines, retired after almost 40 years with Lycoming. Send your questions to: AskPaul@GeneralAviationNews.com.