Originally Posted by rivercreep
On a single cylinder engine that mark will pass the window 2 times.
Once on the compression stroke and once on the intake stroke that draws in your air/fuel mixture.
Minor point, rivercreep, but I believe the TDC mark passes the window at the end of the compression stroke and at the end of the EXHAUST
(not the intake) stroke.
The TDC piston position occurs twice on each cycle of a 4-stroke engine, regardless of the number of cylinders, AFAIK.