----[Please read http://ercoupers.com/disclaimer.htm before following any advice in this forum.]----Don, the reason we are supposed to pull carb heat on our runup is to check to see if it is working. If the rpm didn't drop and then return, it would indicate that the carb heat cable has disconnected itself from the air box. In an earlier post you said you didn't pull carb heat when landing. This is not a good practice. Pulling carb heat anytime the rpm's are at or below 2,000 is a very good idea, since the engine doesn't produce as much heat when you are at low rpms, making carb icing much more possible.
Syd
DONALD BOWEN wrote:
----[Please read http://ercoupers.com/disclaimer.htm before following any advice in this forum.]----Hartmut's comments were excellent, and Paul Anton's chart is useful, too. Yes, carb icing can and does occur here in Florida, despite the fact that I have experienced it only once in nine years of flying. That happened on a cold day (for Florida) in December, flying barely VFR in mist just below an overcast layer at 2000'. The LYCOMING engine lost 150 rpm. Application of carb heat corrected the problem. I am aware that carb ice can build up , on a warm, humid day, even while taxiing. I use a pre-takeoff check following my mag checks. I run the engine up to full, static rpm (2250 or so for my C-90). My brakes are good, so I don't move forward. I pull the carb heat out and watch the rpm drop and stabilize. I then push the carb heat control back in (off), and see if the rpm returns to where it was. I am advised that this check, if it is OK, prevents takeoff attempt with ice in the carburator?
Another handy item for avoiding carb ice, even here in the sunny South, is a Carb Air Temp gage which can be purchased for less than $75. It displays temp right at the carb, not OAT. There can be a great difference in those readings, but the carb temp is the critical one . I believe the icing range is between plus 10 degrees C, and minus 10 degrees C. It is an easy way to check icing temps while airborne. Please do not misinterpret my input as any claim for expertise on my part. Frankly, I don't understand all I know about this subject, and readily admit so.
DON
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