I've heard it said that the RPMs in the range of 1500-1700 (see your plane's manual) were chosen partly for diagnostic reasons. I remember an article where the mag or engine had a certain class of problem that showed up clearly on a low RPM runup but did not show up noticably on a high-speed runup.
The article said it was a general principle to do the runups at that slower 1500-1700 RPM to get better diagnostics. I have no direct knowledge on this subject. Is there a good expert who can confirm or refute this idea? P.S. I also remember the time I heard a strange, irregular pin sound during the normal runup. To diagnose and be sure the engine was OK, I did a full speed runup and heard even more pinging. It turned out the loose gravel under the thin grass was being picked up by the wind and was pinging the prop. The full-power runup gave me several deep dings in that prop. Now I am _very_ careful to look for a safe location for any high power runup. -- Ed Burkhead East Peoria, Ill. N3802H, 415-D
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