carb ice experience

I've probably fired up the Cub 500 times, and every time until the
most recent one went much the same way, just as my instructor taught
me: when you do the mag check (1500 rpm in the Cub) your last check is
pull carb heat on, and watch the rpms drop a bit. Then, if they climb
back to 1500, you know you had a bit of carb ice and that it has
melted, and you will be especially cautious thereafter to avoid icing.

But the other day, first cold day, I had quite a different experience.
The engine may have been running rough when I taxied--hard to know
with earphones, but I had a feel it was rough. Did the mag check.
Pulled carb heat on. Whoom! Rpms went up to 1700.

Now what was the difference between that experience and the ordinary
one where the rpms drop, then rise back to 1500?

Thanks!


-- all the best, Dan Ford

email: usenet AT danford DOT net

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