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I left my choke on????

Roger Lee

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This is posted from another form, but is good info for all.



My wife and I flew up to San Francisco this weekend on our anniversary. She went to watch the Dodgers play at AT&T Park. I went to Fly. The Dodgers played poorly. I didn’t do much better as a pilot.

I usually taxi to the end of the runway at low rpm while the engine is still warming up. But there was a bit of a distraction this time. There were about 20 water-dropping helicopters operating from the median between the taxiway and runway at my home field. I had seen the TFR for the Crown Fire a few miles to the northeast but I had missed the NOTAM which had closed the airport. They let me out anyway, between fire-fighting operations, but it threw off my routine. The choke wasn’t fully closed.

The Rotax 912 “choke” is not really a choke at all, at least not in the classic sense of a plate which restricts (chokes) the flow of air and thus enriches the mixture for starting and warm up. Instead, the Bing carburetor has a separate air and fuel control system with both enriches the mixture and bumps up the rpm. The labeling in my CT2K highlights the difference; the “Open” position is used for starting and the “Closed” position is used for normal operation, exactly the opposite of a classic choke valve.

As I understand it, the Rotax choke function is completely disabled when you advance the throttle so it doesn’t hurt the engine if you forget to close it. In fact, there is no difference in performance at all. You can’t even tell that the choke is partially open… until you pull the throttle back to land.

We decided to stop for lunch at Harris Ranch (a great fly-in restaurant by the way). I thought I had setup a normal pattern, but I was way high on final. Even with the most radical and sustained slip I’ve ever executed, I was still floating down the runway at mid-field. I decided to go around. The next time I got it down by adding more flaps and dragging it in over the weeds. But for a guy who normally lands on the threshold, it was still way long.

Both times around the pattern I keep pulling on the throttle, thinking it must not be all the way back. It wasn’t until I was taxing to the tie downs that I noticed the choke.

The lesson here is this: if you can’t get the plane down, check the choke.


Author was,

Mike Koerner





Hi All,

As a side note the choke, a.k.a. enricher circuit, is not in play after 3500 rpm. If you want to prove it to yourself while flying next time at cruise rpm pull the choke lever open and ..............it will do nothing.

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