Yes, you take temp periodically even after break in. Ambient temperature and general weather changes or terrain changes affect temp, so you check periodically throughout a bash session and adjust tune as needed.
You get used to what an engine sounds like when it's tuned ok over time. Also by keeping an eye on how much smoke comes out of the pipe. No smoke means lean. Or way too rich, usually lean though. You don't usually see much smoke the first few tanks due to it being so rich that it spews actual fuel out. Also, wind blows it away quickly, so sometimes smoke is tough to gauge by.
To see bdc, take your glowplug out, then rotate the flywheel until you see the piston at the bottom of the stroke. Then mark your flywheel by something stationary with nail polish or permanent marker so you can do it in the future without removing the glowplug.
I do it by feel now. Rotate over until I feel compression release, then keep going half a turn.
These engines create compression due to the sleeve inside the engine actually being tapered towards the top. It's called "pinch". New engines have a lot when hot or cold. Broken in engines have pinch when cold, but when the heat up to 200f+, the sleeve expands enough to reduce binding. A worn out engine has too little pinch to create compression when hot, then it's worn out.
In theory, by putting the piston at bdc always (during and after break-in), your helping to preserve the pinch.
