The runup to lean or not to lean?
G'day Bula,
Not to appear sarcastic but you now have all the info in this thread to answer that one yourself.
The answer is both yes and no, it all depends on circumstances.
The points you need to balance up to decide include some of and possibly more of the following:
A good starting point is how hot is your engine right now if you've been taxiing all over the field and it's hot day and your in a tightly cowled aircraft, well you can work out the answer from there.
If your oil temp or cht is above normal again probably not.
Are you in a hurry, if so then probably don't gin about and get going with a conventional runup.
Things are cool and you are in an aircraft with proper engine instruments then you have a lot to gain from a lean runup as a diagnostic tool, particularly diagnostic for the ignition system.
If you have the privelige of always flying one aircraft with proper instrumentation (proper being cht/egt for every jug + fuel flow) then try and lean to the same values each time. This then becomes a bit of a preflight trend monitor. When at significantly different elevations you'll lose the bench mark but still a good educational tool.
For a good diagnostic on the ignition you want try and induce one of the plugs to fail, whether it be the plug that actually fails or the harness or the mag doesn't matter for the initial test. The idea is to create a high combustion pressure so as to increase the sparking resistance and this happens about 40' ROP. Also going to full power would achieve the same, however unless you are over freshly swept concrete this is a bit insulting to your prop and will heat up you engine quite a bit.
I understand that the cht gained during the take off roll is always much the same so if you start with a hot engine it will be even hotter than normal as you cross the upwind end.
The other trick, again only if you have proper instruments other wise it becomes a bit meaningless and confusing is to go so lean that each jug is about to snuff then run a mag check and look at the egt reactions.
Prop cycling should be done full rich if you intend to do it at higher RPM's ie above say 1500 RPM you won't hurt it as rule if you don't but it is easier and quicker to do it rich. Your engine don't much care for being run hard on the ground so anything that reduces the time spent at high power on the ground is a good thing.
It's all a matter of circumstance's
Hope that helps a bit
M